Merge pull request #2672 from kitsunehunter/laundry-keys

[RRG-proxmark3.git] / client / deps / liblua / lstrlib.c

/*
** $Id: lstrlib.c $
** Standard library for string operations and pattern-matching
** See Copyright Notice in lua.h
*/

#define lstrlib_c
#define LUA_LIB

#include "lprefix.h"


#include <ctype.h>
#include <float.h>
#include <limits.h>
#include <locale.h>
#include <math.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "lua.h"

#include "lauxlib.h"
#include "lualib.h"


/*
** maximum number of captures that a pattern can do during
** pattern-matching. This limit is arbitrary, but must fit in
** an unsigned char.
*/
#if !defined(LUA_MAXCAPTURES)
#define LUA_MAXCAPTURES         32
#endif


/* macro to 'unsign' a character */
#define uchar(c)        ((unsigned char)(c))


/*
** Some sizes are better limited to fit in 'int', but must also fit in
** 'size_t'. (We assume that 'lua_Integer' cannot be smaller than 'int'.)
*/
#define MAX_SIZET       ((size_t)(~(size_t)0))

#define MAXSIZE  \
        (sizeof(size_t) < sizeof(int) ? MAX_SIZET : (size_t)(INT_MAX))




static int str_len(lua_State *L) {
    size_t l;
    luaL_checklstring(L, 1, &l);
    lua_pushinteger(L, (lua_Integer)l);
    return 1;
}


/*
** translate a relative initial string position
** (negative means back from end): clip result to [1, inf).
** The length of any string in Lua must fit in a lua_Integer,
** so there are no overflows in the casts.
** The inverted comparison avoids a possible overflow
** computing '-pos'.
*/
static size_t posrelatI(lua_Integer pos, size_t len) {
    if (pos > 0)
        return (size_t)pos;
    else if (pos == 0)
        return 1;
    else if (pos < -(lua_Integer)len)  /* inverted comparison */
        return 1;  /* clip to 1 */
    else return len + (size_t)pos + 1;
}


/*
** Gets an optional ending string position from argument 'arg',
** with default value 'def'.
** Negative means back from end: clip result to [0, len]
*/
static size_t getendpos(lua_State *L, int arg, lua_Integer def,
                        size_t len) {
    lua_Integer pos = luaL_optinteger(L, arg, def);
    if (pos > (lua_Integer)len)
        return len;
    else if (pos >= 0)
        return (size_t)pos;
    else if (pos < -(lua_Integer)len)
        return 0;
    else return len + (size_t)pos + 1;
}


static int str_sub(lua_State *L) {
    size_t l;
    const char *s = luaL_checklstring(L, 1, &l);
    size_t start = posrelatI(luaL_checkinteger(L, 2), l);
    size_t end = getendpos(L, 3, -1, l);
    if (start <= end)
        lua_pushlstring(L, s + start - 1, (end - start) + 1);
    else lua_pushliteral(L, "");
    return 1;
}


static int str_reverse(lua_State *L) {
    size_t l, i;
    luaL_Buffer b;
    const char *s = luaL_checklstring(L, 1, &l);
    char *p = luaL_buffinitsize(L, &b, l);
    for (i = 0; i < l; i++)
        p[i] = s[l - i - 1];
    luaL_pushresultsize(&b, l);
    return 1;
}


static int str_lower(lua_State *L) {
    size_t l;
    size_t i;
    luaL_Buffer b;
    const char *s = luaL_checklstring(L, 1, &l);
    char *p = luaL_buffinitsize(L, &b, l);
    for (i = 0; i < l; i++)
        p[i] = tolower(uchar(s[i]));
    luaL_pushresultsize(&b, l);
    return 1;
}


static int str_upper(lua_State *L) {
    size_t l;
    size_t i;
    luaL_Buffer b;
    const char *s = luaL_checklstring(L, 1, &l);
    char *p = luaL_buffinitsize(L, &b, l);
    for (i = 0; i < l; i++)
        p[i] = toupper(uchar(s[i]));
    luaL_pushresultsize(&b, l);
    return 1;
}


static int str_rep(lua_State *L) {
    size_t l, lsep;
    const char *s = luaL_checklstring(L, 1, &l);
    lua_Integer n = luaL_checkinteger(L, 2);
    const char *sep = luaL_optlstring(L, 3, "", &lsep);
    if (n <= 0)
        lua_pushliteral(L, "");
    else if (l_unlikely(l + lsep < l || l + lsep > MAXSIZE / n))
        return luaL_error(L, "resulting string too large");
    else {
        size_t totallen = (size_t)n * l + (size_t)(n - 1) * lsep;
        luaL_Buffer b;
        char *p = luaL_buffinitsize(L, &b, totallen);
        while (n-- > 1) {  /* first n-1 copies (followed by separator) */
            memcpy(p, s, l * sizeof(char));
            p += l;
            if (lsep > 0) {  /* empty 'memcpy' is not that cheap */
                memcpy(p, sep, lsep * sizeof(char));
                p += lsep;
            }
        }
        memcpy(p, s, l * sizeof(char));  /* last copy (not followed by separator) */
        luaL_pushresultsize(&b, totallen);
    }
    return 1;
}


static int str_byte(lua_State *L) {
    size_t l;
    const char *s = luaL_checklstring(L, 1, &l);
    lua_Integer pi = luaL_optinteger(L, 2, 1);
    size_t posi = posrelatI(pi, l);
    size_t pose = getendpos(L, 3, pi, l);
    int n, i;
    if (posi > pose) return 0;  /* empty interval; return no values */
    if (l_unlikely(pose - posi >= (size_t)INT_MAX))  /* arithmetic overflow? */
        return luaL_error(L, "string slice too long");
    n = (int)(pose -  posi) + 1;
    luaL_checkstack(L, n, "string slice too long");
    for (i = 0; i < n; i++)
        lua_pushinteger(L, uchar(s[posi + i - 1]));
    return n;
}


static int str_char(lua_State *L) {
    int n = lua_gettop(L);  /* number of arguments */
    int i;
    luaL_Buffer b;
    char *p = luaL_buffinitsize(L, &b, n);
    for (i = 1; i <= n; i++) {
        lua_Unsigned c = (lua_Unsigned)luaL_checkinteger(L, i);
        luaL_argcheck(L, c <= (lua_Unsigned)UCHAR_MAX, i, "value out of range");
        p[i - 1] = uchar(c);
    }
    luaL_pushresultsize(&b, n);
    return 1;
}


/*
** Buffer to store the result of 'string.dump'. It must be initialized
** after the call to 'lua_dump', to ensure that the function is on the
** top of the stack when 'lua_dump' is called. ('luaL_buffinit' might
** push stuff.)
*/
struct str_Writer {
    int init;  /* true iff buffer has been initialized */
    luaL_Buffer B;
};


static int writer(lua_State *L, const void *b, size_t size, void *ud) {
    struct str_Writer *state = (struct str_Writer *)ud;
    if (!state->init) {
        state->init = 1;
        luaL_buffinit(L, &state->B);
    }
    luaL_addlstring(&state->B, (const char *)b, size);
    return 0;
}


static int str_dump(lua_State *L) {
    struct str_Writer state;
    int strip = lua_toboolean(L, 2);
    luaL_checktype(L, 1, LUA_TFUNCTION);
    lua_settop(L, 1);  /* ensure function is on the top of the stack */
    state.init = 0;
    if (l_unlikely(lua_dump(L, writer, &state, strip) != 0))
        return luaL_error(L, "unable to dump given function");
    luaL_pushresult(&state.B);
    return 1;
}



/*
** {======================================================
** METAMETHODS
** =======================================================
*/

#if defined(LUA_NOCVTS2N)       /* { */

/* no coercion from strings to numbers */

static const luaL_Reg stringmetamethods[] = {
    {"__index", NULL},  /* placeholder */
    {NULL, NULL}
};

#else           /* }{ */

static int tonum(lua_State *L, int arg) {
    if (lua_type(L, arg) == LUA_TNUMBER) {  /* already a number? */
        lua_pushvalue(L, arg);
        return 1;
    } else { /* check whether it is a numerical string */
        size_t len;
        const char *s = lua_tolstring(L, arg, &len);
        return (s != NULL && lua_stringtonumber(L, s) == len + 1);
    }
}


static void trymt(lua_State *L, const char *mtname) {
    lua_settop(L, 2);  /* back to the original arguments */
    if (l_unlikely(lua_type(L, 2) == LUA_TSTRING ||
                   !luaL_getmetafield(L, 2, mtname)))
        luaL_error(L, "attempt to %s a '%s' with a '%s'", mtname + 2,
                   luaL_typename(L, -2), luaL_typename(L, -1));
    lua_insert(L, -3);  /* put metamethod before arguments */
    lua_call(L, 2, 1);  /* call metamethod */
}


static int arith(lua_State *L, int op, const char *mtname) {
    if (tonum(L, 1) && tonum(L, 2))
        lua_arith(L, op);  /* result will be on the top */
    else
        trymt(L, mtname);
    return 1;
}


static int arith_add(lua_State *L) {
    return arith(L, LUA_OPADD, "__add");
}

static int arith_sub(lua_State *L) {
    return arith(L, LUA_OPSUB, "__sub");
}

static int arith_mul(lua_State *L) {
    return arith(L, LUA_OPMUL, "__mul");
}

static int arith_mod(lua_State *L) {
    return arith(L, LUA_OPMOD, "__mod");
}

static int arith_pow(lua_State *L) {
    return arith(L, LUA_OPPOW, "__pow");
}

static int arith_div(lua_State *L) {
    return arith(L, LUA_OPDIV, "__div");
}

static int arith_idiv(lua_State *L) {
    return arith(L, LUA_OPIDIV, "__idiv");
}

static int arith_unm(lua_State *L) {
    return arith(L, LUA_OPUNM, "__unm");
}


static const luaL_Reg stringmetamethods[] = {
    {"__add", arith_add},
    {"__sub", arith_sub},
    {"__mul", arith_mul},
    {"__mod", arith_mod},
    {"__pow", arith_pow},
    {"__div", arith_div},
    {"__idiv", arith_idiv},
    {"__unm", arith_unm},
    {"__index", NULL},  /* placeholder */
    {NULL, NULL}
};

#endif          /* } */

/* }====================================================== */

/*
** {======================================================
** PATTERN MATCHING
** =======================================================
*/


#define CAP_UNFINISHED  (-1)
#define CAP_POSITION    (-2)


typedef struct MatchState {
    const char *src_init;  /* init of source string */
    const char *src_end;  /* end ('\0') of source string */
    const char *p_end;  /* end ('\0') of pattern */
    lua_State *L;
    int matchdepth;  /* control for recursive depth (to avoid C stack overflow) */
    unsigned char level;  /* total number of captures (finished or unfinished) */
    struct {
        const char *init;
        ptrdiff_t len;
    } capture[LUA_MAXCAPTURES];
} MatchState;


/* recursive function */
static const char *match(MatchState *ms, const char *s, const char *p);


/* maximum recursion depth for 'match' */
#if !defined(MAXCCALLS)
#define MAXCCALLS       200
#endif


#define L_ESC           '%'
#define SPECIALS        "^$*+?.([%-"


static int check_capture(MatchState *ms, int l) {
    l -= '1';
    if (l_unlikely(l < 0 || l >= ms->level ||
                   ms->capture[l].len == CAP_UNFINISHED))
        return luaL_error(ms->L, "invalid capture index %%%d", l + 1);
    return l;
}


static int capture_to_close(MatchState *ms) {
    int level = ms->level;
    for (level--; level >= 0; level--)
        if (ms->capture[level].len == CAP_UNFINISHED) return level;
    return luaL_error(ms->L, "invalid pattern capture");
}


static const char *classend(MatchState *ms, const char *p) {
    switch (*p++) {
        case L_ESC: {
            if (l_unlikely(p == ms->p_end))
                luaL_error(ms->L, "malformed pattern (ends with '%%')");
            return p + 1;
        }
        case '[': {
            if (*p == '^') p++;
            do {  /* look for a ']' */
                if (l_unlikely(p == ms->p_end))
                    luaL_error(ms->L, "malformed pattern (missing ']')");
                if (*(p++) == L_ESC && p < ms->p_end)
                    p++;  /* skip escapes (e.g. '%]') */
            } while (*p != ']');
            return p + 1;
        }
        default: {
            return p;
        }
    }
}


static int match_class(int c, int cl) {
    int res;
    switch (tolower(cl)) {
        case 'a' :
            res = isalpha(c);
            break;
        case 'c' :
            res = iscntrl(c);
            break;
        case 'd' :
            res = isdigit(c);
            break;
        case 'g' :
            res = isgraph(c);
            break;
        case 'l' :
            res = islower(c);
            break;
        case 'p' :
            res = ispunct(c);
            break;
        case 's' :
            res = isspace(c);
            break;
        case 'u' :
            res = isupper(c);
            break;
        case 'w' :
            res = isalnum(c);
            break;
        case 'x' :
            res = isxdigit(c);
            break;
        case 'z' :
            res = (c == 0);
            break;  /* deprecated option */
        default:
            return (cl == c);
    }
    return (islower(cl) ? res : !res);
}


static int matchbracketclass(int c, const char *p, const char *ec) {
    int sig = 1;
    if (*(p + 1) == '^') {
        sig = 0;
        p++;  /* skip the '^' */
    }
    while (++p < ec) {
        if (*p == L_ESC) {
            p++;
            if (match_class(c, uchar(*p)))
                return sig;
        } else if ((*(p + 1) == '-') && (p + 2 < ec)) {
            p += 2;
            if (uchar(*(p - 2)) <= c && c <= uchar(*p))
                return sig;
        } else if (uchar(*p) == c) return sig;
    }
    return !sig;
}


static int singlematch(MatchState *ms, const char *s, const char *p,
                       const char *ep) {
    if (s >= ms->src_end)
        return 0;
    else {
        int c = uchar(*s);
        switch (*p) {
            case '.':
                return 1;  /* matches any char */
            case L_ESC:
                return match_class(c, uchar(*(p + 1)));
            case '[':
                return matchbracketclass(c, p, ep - 1);
            default:
                return (uchar(*p) == c);
        }
    }
}


static const char *matchbalance(MatchState *ms, const char *s,
                                const char *p) {
    if (l_unlikely(p >= ms->p_end - 1))
        luaL_error(ms->L, "malformed pattern (missing arguments to '%%b')");
    if (*s != *p) return NULL;
    else {
        int b = *p;
        int e = *(p + 1);
        int cont = 1;
        while (++s < ms->src_end) {
            if (*s == e) {
                if (--cont == 0) return s + 1;
            } else if (*s == b) cont++;
        }
    }
    return NULL;  /* string ends out of balance */
}


static const char *max_expand(MatchState *ms, const char *s,
                              const char *p, const char *ep) {
    ptrdiff_t i = 0;  /* counts maximum expand for item */
    while (singlematch(ms, s + i, p, ep))
        i++;
    /* keeps trying to match with the maximum repetitions */
    while (i >= 0) {
        const char *res = match(ms, (s + i), ep + 1);
        if (res) return res;
        i--;  /* else didn't match; reduce 1 repetition to try again */
    }
    return NULL;
}


static const char *min_expand(MatchState *ms, const char *s,
                              const char *p, const char *ep) {
    for (;;) {
        const char *res = match(ms, s, ep + 1);
        if (res != NULL)
            return res;
        else if (singlematch(ms, s, p, ep))
            s++;  /* try with one more repetition */
        else return NULL;
    }
}


static const char *start_capture(MatchState *ms, const char *s,
                                 const char *p, int what) {
    const char *res;
    int level = ms->level;
    if (level >= LUA_MAXCAPTURES) luaL_error(ms->L, "too many captures");
    ms->capture[level].init = s;
    ms->capture[level].len = what;
    ms->level = level + 1;
    if ((res = match(ms, s, p)) == NULL) /* match failed? */
        ms->level--;  /* undo capture */
    return res;
}


static const char *end_capture(MatchState *ms, const char *s,
                               const char *p) {
    int l = capture_to_close(ms);
    const char *res;
    ms->capture[l].len = s - ms->capture[l].init;  /* close capture */
    if ((res = match(ms, s, p)) == NULL)  /* match failed? */
        ms->capture[l].len = CAP_UNFINISHED;  /* undo capture */
    return res;
}


static const char *match_capture(MatchState *ms, const char *s, int l) {
    size_t len;
    l = check_capture(ms, l);
    len = ms->capture[l].len;
    if ((size_t)(ms->src_end - s) >= len &&
            memcmp(ms->capture[l].init, s, len) == 0)
        return s + len;
    else return NULL;
}


static const char *match(MatchState *ms, const char *s, const char *p) {
    if (l_unlikely(ms->matchdepth-- == 0))
        luaL_error(ms->L, "pattern too complex");
init: /* using goto to optimize tail recursion */
    if (p != ms->p_end) {  /* end of pattern? */
        switch (*p) {
            case '(': {  /* start capture */
                if (*(p + 1) == ')')  /* position capture? */
                    s = start_capture(ms, s, p + 2, CAP_POSITION);
                else
                    s = start_capture(ms, s, p + 1, CAP_UNFINISHED);
                break;
            }
            case ')': {  /* end capture */
                s = end_capture(ms, s, p + 1);
                break;
            }
            case '$': {
                if ((p + 1) != ms->p_end)  /* is the '$' the last char in pattern? */
                    goto dflt;  /* no; go to default */
                s = (s == ms->src_end) ? s : NULL;  /* check end of string */
                break;
            }
            case L_ESC: {  /* escaped sequences not in the format class[*+?-]? */
                switch (*(p + 1)) {
                    case 'b': {  /* balanced string? */
                        s = matchbalance(ms, s, p + 2);
                        if (s != NULL) {
                            p += 4;
                            goto init;  /* return match(ms, s, p + 4); */
                        }  /* else fail (s == NULL) */
                        break;
                    }
                    case 'f': {  /* frontier? */
                        const char *ep;
                        char previous;
                        p += 2;
                        if (l_unlikely(*p != '['))
                            luaL_error(ms->L, "missing '[' after '%%f' in pattern");
                        ep = classend(ms, p);  /* points to what is next */
                        previous = (s == ms->src_init) ? '\0' : *(s - 1);
                        if (!matchbracketclass(uchar(previous), p, ep - 1) &&
                                matchbracketclass(uchar(*s), p, ep - 1)) {
                            p = ep;
                            goto init;  /* return match(ms, s, ep); */
                        }
                        s = NULL;  /* match failed */
                        break;
                    }
                    case '0':
                    case '1':
                    case '2':
                    case '3':
                    case '4':
                    case '5':
                    case '6':
                    case '7':
                    case '8':
                    case '9': {  /* capture results (%0-%9)? */
                        s = match_capture(ms, s, uchar(*(p + 1)));
                        if (s != NULL) {
                            p += 2;
                            goto init;  /* return match(ms, s, p + 2) */
                        }
                        break;
                    }
                    default:
                        goto dflt;
                }
                break;
            }
            default:
dflt: {  /* pattern class plus optional suffix */
                    const char *ep = classend(ms, p);  /* points to optional suffix */
                    /* does not match at least once? */
                    if (!singlematch(ms, s, p, ep)) {
                        if (*ep == '*' || *ep == '?' || *ep == '-') {  /* accept empty? */
                            p = ep + 1;
                            goto init;  /* return match(ms, s, ep + 1); */
                        } else /* '+' or no suffix */
                            s = NULL;  /* fail */
                    } else { /* matched once */
                        switch (*ep) {  /* handle optional suffix */
                            case '?': {  /* optional */
                                const char *res;
                                if ((res = match(ms, s + 1, ep + 1)) != NULL)
                                    s = res;
                                else {
                                    p = ep + 1;
                                    goto init;  /* else return match(ms, s, ep + 1); */
                                }
                                break;
                            }
                            case '+':  /* 1 or more repetitions */
                                s++;  /* 1 match already done */
                            /* FALLTHROUGH */
                            case '*':  /* 0 or more repetitions */
                                s = max_expand(ms, s, p, ep);
                                break;
                            case '-':  /* 0 or more repetitions (minimum) */
                                s = min_expand(ms, s, p, ep);
                                break;
                            default:  /* no suffix */
                                s++;
                                p = ep;
                                goto init;  /* return match(ms, s + 1, ep); */
                        }
                    }
                    break;
                }
        }
    }
    ms->matchdepth++;
    return s;
}



static const char *lmemfind(const char *s1, size_t l1,
                            const char *s2, size_t l2) {
    if (l2 == 0) return s1;  /* empty strings are everywhere */
    else if (l2 > l1) return NULL;  /* avoids a negative 'l1' */
    else {
        const char *init;  /* to search for a '*s2' inside 's1' */
        l2--;  /* 1st char will be checked by 'memchr' */
        l1 = l1 - l2; /* 's2' cannot be found after that */
        while (l1 > 0 && (init = (const char *)memchr(s1, *s2, l1)) != NULL) {
            init++;   /* 1st char is already checked */
            if (memcmp(init, s2 + 1, l2) == 0)
                return init - 1;
            else {  /* correct 'l1' and 's1' to try again */
                l1 -= init - s1;
                s1 = init;
            }
        }
        return NULL;  /* not found */
    }
}


/*
** get information about the i-th capture. If there are no captures
** and 'i==0', return information about the whole match, which
** is the range 's'..'e'. If the capture is a string, return
** its length and put its address in '*cap'. If it is an integer
** (a position), push it on the stack and return CAP_POSITION.
*/
static size_t get_onecapture(MatchState *ms, int i, const char *s,
                             const char *e, const char **cap) {
    if (i >= ms->level) {
        if (l_unlikely(i != 0))
            luaL_error(ms->L, "invalid capture index %%%d", i + 1);
        *cap = s;
        return e - s;
    } else {
        ptrdiff_t capl = ms->capture[i].len;
        *cap = ms->capture[i].init;
        if (l_unlikely(capl == CAP_UNFINISHED))
            luaL_error(ms->L, "unfinished capture");
        else if (capl == CAP_POSITION)
            lua_pushinteger(ms->L, (ms->capture[i].init - ms->src_init) + 1);
        return capl;
    }
}


/*
** Push the i-th capture on the stack.
*/
static void push_onecapture(MatchState *ms, int i, const char *s,
                            const char *e) {
    const char *cap;
    ptrdiff_t l = get_onecapture(ms, i, s, e, &cap);
    if (l != CAP_POSITION)
        lua_pushlstring(ms->L, cap, l);
    /* else position was already pushed */
}


static int push_captures(MatchState *ms, const char *s, const char *e) {
    int i;
    int nlevels = (ms->level == 0 && s) ? 1 : ms->level;
    luaL_checkstack(ms->L, nlevels, "too many captures");
    for (i = 0; i < nlevels; i++)
        push_onecapture(ms, i, s, e);
    return nlevels;  /* number of strings pushed */
}


/* check whether pattern has no special characters */
static int nospecials(const char *p, size_t l) {
    size_t upto = 0;
    do {
        if (strpbrk(p + upto, SPECIALS))
            return 0;  /* pattern has a special character */
        upto += strlen(p + upto) + 1;  /* may have more after \0 */
    } while (upto <= l);
    return 1;  /* no special chars found */
}


static void prepstate(MatchState *ms, lua_State *L,
                      const char *s, size_t ls, const char *p, size_t lp) {
    ms->L = L;
    ms->matchdepth = MAXCCALLS;
    ms->src_init = s;
    ms->src_end = s + ls;
    ms->p_end = p + lp;
}


static void reprepstate(MatchState *ms) {
    ms->level = 0;
    lua_assert(ms->matchdepth == MAXCCALLS);
}


static int str_find_aux(lua_State *L, int find) {
    size_t ls, lp;
    const char *s = luaL_checklstring(L, 1, &ls);
    const char *p = luaL_checklstring(L, 2, &lp);
    size_t init = posrelatI(luaL_optinteger(L, 3, 1), ls) - 1;
    if (init > ls) {  /* start after string's end? */
        luaL_pushfail(L);  /* cannot find anything */
        return 1;
    }
    /* explicit request or no special characters? */
    if (find && (lua_toboolean(L, 4) || nospecials(p, lp))) {
        /* do a plain search */
        const char *s2 = lmemfind(s + init, ls - init, p, lp);
        if (s2) {
            lua_pushinteger(L, (s2 - s) + 1);
            lua_pushinteger(L, (s2 - s) + lp);
            return 2;
        }
    } else {
        MatchState ms;
        const char *s1 = s + init;
        int anchor = (*p == '^');
        if (anchor) {
            p++;
            lp--;  /* skip anchor character */
        }
        prepstate(&ms, L, s, ls, p, lp);
        do {
            const char *res;
            reprepstate(&ms);
            if ((res = match(&ms, s1, p)) != NULL) {
                if (find) {
                    lua_pushinteger(L, (s1 - s) + 1);  /* start */
                    lua_pushinteger(L, res - s);   /* end */
                    return push_captures(&ms, NULL, 0) + 2;
                } else
                    return push_captures(&ms, s1, res);
            }
        } while (s1++ < ms.src_end && !anchor);
    }
    luaL_pushfail(L);  /* not found */
    return 1;
}


static int str_find(lua_State *L) {
    return str_find_aux(L, 1);
}


static int str_match(lua_State *L) {
    return str_find_aux(L, 0);
}


/* state for 'gmatch' */
typedef struct GMatchState {
    const char *src;  /* current position */
    const char *p;  /* pattern */
    const char *lastmatch;  /* end of last match */
    MatchState ms;  /* match state */
} GMatchState;


static int gmatch_aux(lua_State *L) {
    GMatchState *gm = (GMatchState *)lua_touserdata(L, lua_upvalueindex(3));
    const char *src;
    gm->ms.L = L;
    for (src = gm->src; src <= gm->ms.src_end; src++) {
        const char *e;
        reprepstate(&gm->ms);
        if ((e = match(&gm->ms, src, gm->p)) != NULL && e != gm->lastmatch) {
            gm->src = gm->lastmatch = e;
            return push_captures(&gm->ms, src, e);
        }
    }
    return 0;  /* not found */
}


static int gmatch(lua_State *L) {
    size_t ls, lp;
    const char *s = luaL_checklstring(L, 1, &ls);
    const char *p = luaL_checklstring(L, 2, &lp);
    size_t init = posrelatI(luaL_optinteger(L, 3, 1), ls) - 1;
    GMatchState *gm;
    lua_settop(L, 2);  /* keep strings on closure to avoid being collected */
    gm = (GMatchState *)lua_newuserdatauv(L, sizeof(GMatchState), 0);
    if (init > ls)  /* start after string's end? */
        init = ls + 1;  /* avoid overflows in 's + init' */
    prepstate(&gm->ms, L, s, ls, p, lp);
    gm->src = s + init;
    gm->p = p;
    gm->lastmatch = NULL;
    lua_pushcclosure(L, gmatch_aux, 3);
    return 1;
}


static void add_s(MatchState *ms, luaL_Buffer *b, const char *s,
                  const char *e) {
    size_t l;
    lua_State *L = ms->L;
    const char *news = lua_tolstring(L, 3, &l);
    const char *p;
    while ((p = (char *)memchr(news, L_ESC, l)) != NULL) {
        luaL_addlstring(b, news, p - news);
        p++;  /* skip ESC */
        if (*p == L_ESC)  /* '%%' */
            luaL_addchar(b, *p);
        else if (*p == '0')  /* '%0' */
            luaL_addlstring(b, s, e - s);
        else if (isdigit(uchar(*p))) {  /* '%n' */
            const char *cap;
            ptrdiff_t resl = get_onecapture(ms, *p - '1', s, e, &cap);
            if (resl == CAP_POSITION)
                luaL_addvalue(b);  /* add position to accumulated result */
            else
                luaL_addlstring(b, cap, resl);
        } else
            luaL_error(L, "invalid use of '%c' in replacement string", L_ESC);
        l -= p + 1 - news;
        news = p + 1;
    }
    luaL_addlstring(b, news, l);
}


/*
** Add the replacement value to the string buffer 'b'.
** Return true if the original string was changed. (Function calls and
** table indexing resulting in nil or false do not change the subject.)
*/
static int add_value(MatchState *ms, luaL_Buffer *b, const char *s,
                     const char *e, int tr) {
    lua_State *L = ms->L;
    switch (tr) {
        case LUA_TFUNCTION: {  /* call the function */
            int n;
            lua_pushvalue(L, 3);  /* push the function */
            n = push_captures(ms, s, e);  /* all captures as arguments */
            lua_call(L, n, 1);  /* call it */
            break;
        }
        case LUA_TTABLE: {  /* index the table */
            push_onecapture(ms, 0, s, e);  /* first capture is the index */
            lua_gettable(L, 3);
            break;
        }
        default: {  /* LUA_TNUMBER or LUA_TSTRING */
            add_s(ms, b, s, e);  /* add value to the buffer */
            return 1;  /* something changed */
        }
    }
    if (!lua_toboolean(L, -1)) {  /* nil or false? */
        lua_pop(L, 1);  /* remove value */
        luaL_addlstring(b, s, e - s);  /* keep original text */
        return 0;  /* no changes */
    } else if (l_unlikely(!lua_isstring(L, -1)))
        return luaL_error(L, "invalid replacement value (a %s)",
                          luaL_typename(L, -1));
    else {
        luaL_addvalue(b);  /* add result to accumulator */
        return 1;  /* something changed */
    }
}


static int str_gsub(lua_State *L) {
    size_t srcl, lp;
    const char *src = luaL_checklstring(L, 1, &srcl);  /* subject */
    const char *p = luaL_checklstring(L, 2, &lp);  /* pattern */
    const char *lastmatch = NULL;  /* end of last match */
    int tr = lua_type(L, 3);  /* replacement type */
    lua_Integer max_s = luaL_optinteger(L, 4, srcl + 1);  /* max replacements */
    int anchor = (*p == '^');
    lua_Integer n = 0;  /* replacement count */
    int changed = 0;  /* change flag */
    MatchState ms;
    luaL_Buffer b;
    luaL_argexpected(L, tr == LUA_TNUMBER || tr == LUA_TSTRING ||
                     tr == LUA_TFUNCTION || tr == LUA_TTABLE, 3,
                     "string/function/table");
    luaL_buffinit(L, &b);
    if (anchor) {
        p++;
        lp--;  /* skip anchor character */
    }
    prepstate(&ms, L, src, srcl, p, lp);
    while (n < max_s) {
        const char *e;
        reprepstate(&ms);  /* (re)prepare state for new match */
        if ((e = match(&ms, src, p)) != NULL && e != lastmatch) {  /* match? */
            n++;
            changed = add_value(&ms, &b, src, e, tr) | changed;
            src = lastmatch = e;
        } else if (src < ms.src_end) /* otherwise, skip one character */
            luaL_addchar(&b, *src++);
        else break;  /* end of subject */
        if (anchor) break;
    }
    if (!changed)  /* no changes? */
        lua_pushvalue(L, 1);  /* return original string */
    else {  /* something changed */
        luaL_addlstring(&b, src, ms.src_end - src);
        luaL_pushresult(&b);  /* create and return new string */
    }
    lua_pushinteger(L, n);  /* number of substitutions */
    return 2;
}

/* }====================================================== */



/*
** {======================================================
** STRING FORMAT
** =======================================================
*/

#if !defined(lua_number2strx)   /* { */

/*
** Hexadecimal floating-point formatter
*/

#define SIZELENMOD      (sizeof(LUA_NUMBER_FRMLEN)/sizeof(char))


/*
** Number of bits that goes into the first digit. It can be any value
** between 1 and 4; the following definition tries to align the number
** to nibble boundaries by making what is left after that first digit a
** multiple of 4.
*/
#define L_NBFD          ((l_floatatt(MANT_DIG) - 1)%4 + 1)


/*
** Add integer part of 'x' to buffer and return new 'x'
*/
static lua_Number adddigit(char *buff, int n, lua_Number x) {
    lua_Number dd = l_mathop(floor)(x);  /* get integer part from 'x' */
    int d = (int)dd;
    buff[n] = (d < 10 ? d + '0' : d - 10 + 'a');  /* add to buffer */
    return x - dd;  /* return what is left */
}


static int num2straux(char *buff, int sz, lua_Number x) {
    /* if 'inf' or 'NaN', format it like '%g' */
    if (x != x || x == (lua_Number)HUGE_VAL || x == -(lua_Number)HUGE_VAL)
        return l_sprintf(buff, sz, LUA_NUMBER_FMT, (LUAI_UACNUMBER)x);
    else if (x == 0) {  /* can be -0... */
        /* create "0" or "-0" followed by exponent */
        return l_sprintf(buff, sz, LUA_NUMBER_FMT "x0p+0", (LUAI_UACNUMBER)x);
    } else {
        int e;
        lua_Number m = l_mathop(frexp)(x, &e);  /* 'x' fraction and exponent */
        int n = 0;  /* character count */
        if (m < 0) {  /* is number negative? */
            buff[n++] = '-';  /* add sign */
            m = -m;  /* make it positive */
        }
        buff[n++] = '0';
        buff[n++] = 'x';  /* add "0x" */
        m = adddigit(buff, n++, m * (1 << L_NBFD));  /* add first digit */
        e -= L_NBFD;  /* this digit goes before the radix point */
        if (m > 0) {  /* more digits? */
            buff[n++] = lua_getlocaledecpoint();  /* add radix point */
            do {  /* add as many digits as needed */
                m = adddigit(buff, n++, m * 16);
            } while (m > 0);
        }
        n += l_sprintf(buff + n, sz - n, "p%+d", e);  /* add exponent */
        lua_assert(n < sz);
        return n;
    }
}


static int lua_number2strx(lua_State *L, char *buff, int sz,
                           const char *fmt, lua_Number x) {
    int n = num2straux(buff, sz, x);
    if (fmt[SIZELENMOD] == 'A') {
        int i;
        for (i = 0; i < n; i++)
            buff[i] = toupper(uchar(buff[i]));
    } else if (l_unlikely(fmt[SIZELENMOD] != 'a'))
        return luaL_error(L, "modifiers for format '%%a'/'%%A' not implemented");
    return n;
}

#endif                          /* } */


/*
** Maximum size for items formatted with '%f'. This size is produced
** by format('%.99f', -maxfloat), and is equal to 99 + 3 ('-', '.',
** and '\0') + number of decimal digits to represent maxfloat (which
** is maximum exponent + 1). (99+3+1, adding some extra, 110)
*/
#define MAX_ITEMF       (110 + l_floatatt(MAX_10_EXP))


/*
** All formats except '%f' do not need that large limit.  The other
** float formats use exponents, so that they fit in the 99 limit for
** significant digits; 's' for large strings and 'q' add items directly
** to the buffer; all integer formats also fit in the 99 limit.  The
** worst case are floats: they may need 99 significant digits, plus
** '0x', '-', '.', 'e+XXXX', and '\0'. Adding some extra, 120.
*/
#define MAX_ITEM        120


/* valid flags in a format specification */
#if !defined(L_FMTFLAGSF)

/* valid flags for a, A, e, E, f, F, g, and G conversions */
#define L_FMTFLAGSF     "-+#0 "

/* valid flags for o, x, and X conversions */
#define L_FMTFLAGSX     "-#0"

/* valid flags for d and i conversions */
#define L_FMTFLAGSI     "-+0 "

/* valid flags for u conversions */
#define L_FMTFLAGSU     "-0"

/* valid flags for c, p, and s conversions */
#define L_FMTFLAGSC     "-"

#endif


/*
** Maximum size of each format specification (such as "%-099.99d"):
** Initial '%', flags (up to 5), width (2), period, precision (2),
** length modifier (8), conversion specifier, and final '\0', plus some
** extra.
*/
#define MAX_FORMAT      32


static void addquoted(luaL_Buffer *b, const char *s, size_t len) {
    luaL_addchar(b, '"');
    while (len--) {
        if (*s == '"' || *s == '\\' || *s == '\n') {
            luaL_addchar(b, '\\');
            luaL_addchar(b, *s);
        } else if (iscntrl(uchar(*s))) {
            char buff[10];
            if (!isdigit(uchar(*(s + 1))))
                l_sprintf(buff, sizeof(buff), "\\%d", (int)uchar(*s));
            else
                l_sprintf(buff, sizeof(buff), "\\%03d", (int)uchar(*s));
            luaL_addstring(b, buff);
        } else
            luaL_addchar(b, *s);
        s++;
    }
    luaL_addchar(b, '"');
}


/*
** Serialize a floating-point number in such a way that it can be
** scanned back by Lua. Use hexadecimal format for "common" numbers
** (to preserve precision); inf, -inf, and NaN are handled separately.
** (NaN cannot be expressed as a numeral, so we write '(0/0)' for it.)
*/
static int quotefloat(lua_State *L, char *buff, lua_Number n) {
    const char *s;  /* for the fixed representations */
    if (n == (lua_Number)HUGE_VAL)  /* inf? */
        s = "1e9999";
    else if (n == -(lua_Number)HUGE_VAL)  /* -inf? */
        s = "-1e9999";
    else if (n != n)  /* NaN? */
        s = "(0/0)";
    else {  /* format number as hexadecimal */
        int  nb = lua_number2strx(L, buff, MAX_ITEM,
                                  "%" LUA_NUMBER_FRMLEN "a", n);
        /* ensures that 'buff' string uses a dot as the radix character */
        if (memchr(buff, '.', nb) == NULL) {  /* no dot? */
            char point = lua_getlocaledecpoint();  /* try locale point */
            char *ppoint = (char *)memchr(buff, point, nb);
            if (ppoint) *ppoint = '.';  /* change it to a dot */
        }
        return nb;
    }
    /* for the fixed representations */
    return l_sprintf(buff, MAX_ITEM, "%s", s);
}


static void addliteral(lua_State *L, luaL_Buffer *b, int arg) {
    switch (lua_type(L, arg)) {
        case LUA_TSTRING: {
            size_t len;
            const char *s = lua_tolstring(L, arg, &len);
            addquoted(b, s, len);
            break;
        }
        case LUA_TNUMBER: {
            char *buff = luaL_prepbuffsize(b, MAX_ITEM);
            int nb;
            if (!lua_isinteger(L, arg))  /* float? */
                nb = quotefloat(L, buff, lua_tonumber(L, arg));
            else {  /* integers */
                lua_Integer n = lua_tointeger(L, arg);
                const char *format = (n == LUA_MININTEGER)  /* corner case? */
                                     ? "0x%" LUA_INTEGER_FRMLEN "x"  /* use hex */
                                     : LUA_INTEGER_FMT;  /* else use default format */
                nb = l_sprintf(buff, MAX_ITEM, format, (LUAI_UACINT)n);
            }
            luaL_addsize(b, nb);
            break;
        }
        case LUA_TNIL:
        case LUA_TBOOLEAN: {
            luaL_tolstring(L, arg, NULL);
            luaL_addvalue(b);
            break;
        }
        default: {
            luaL_argerror(L, arg, "value has no literal form");
        }
    }
}


static const char *get2digits(const char *s) {
    if (isdigit(uchar(*s))) {
        s++;
        if (isdigit(uchar(*s))) s++;  /* (2 digits at most) */
    }
    return s;
}


/*
** Check whether a conversion specification is valid. When called,
** first character in 'form' must be '%' and last character must
** be a valid conversion specifier. 'flags' are the accepted flags;
** 'precision' signals whether to accept a precision.
*/
static void checkformat(lua_State *L, const char *form, const char *flags,
                        int precision) {
    const char *spec = form + 1;  /* skip '%' */
    spec += strspn(spec, flags);  /* skip flags */
    if (*spec != '0') {  /* a width cannot start with '0' */
        spec = get2digits(spec);  /* skip width */
        if (*spec == '.' && precision) {
            spec++;
            spec = get2digits(spec);  /* skip precision */
        }
    }
    if (!isalpha(uchar(*spec)))  /* did not go to the end? */
        luaL_error(L, "invalid conversion specification: '%s'", form);
}


/*
** Get a conversion specification and copy it to 'form'.
** Return the address of its last character.
*/
static const char *getformat(lua_State *L, const char *strfrmt,
                             char *form) {
    /* spans flags, width, and precision ('0' is included as a flag) */
    size_t len = strspn(strfrmt, L_FMTFLAGSF "123456789.");
    len++;  /* adds following character (should be the specifier) */
    /* still needs space for '%', '\0', plus a length modifier */
    if (len >= MAX_FORMAT - 10)
        luaL_error(L, "invalid format (too long)");
    *(form++) = '%';
    memcpy(form, strfrmt, len * sizeof(char));
    *(form + len) = '\0';
    return strfrmt + len - 1;
}


/*
** add length modifier into formats
*/
static void addlenmod(char *form, const char *lenmod) {
    size_t l = strlen(form);
    size_t lm = strlen(lenmod);
    char spec = form[l - 1];
    strcpy(form + l - 1, lenmod);
    form[l + lm - 1] = spec;
    form[l + lm] = '\0';
}


static int str_format(lua_State *L) {
    int top = lua_gettop(L);
    int arg = 1;
    size_t sfl;
    const char *strfrmt = luaL_checklstring(L, arg, &sfl);
    const char *strfrmt_end = strfrmt + sfl;
    const char *flags;
    luaL_Buffer b;
    luaL_buffinit(L, &b);
    while (strfrmt < strfrmt_end) {
        if (*strfrmt != L_ESC)
            luaL_addchar(&b, *strfrmt++);
        else if (*++strfrmt == L_ESC)
            luaL_addchar(&b, *strfrmt++);  /* %% */
        else { /* format item */
            char form[MAX_FORMAT];  /* to store the format ('%...') */
            int maxitem = MAX_ITEM;  /* maximum length for the result */
            char *buff = luaL_prepbuffsize(&b, maxitem);  /* to put result */
            int nb = 0;  /* number of bytes in result */
            if (++arg > top)
                return luaL_argerror(L, arg, "no value");
            strfrmt = getformat(L, strfrmt, form);
            switch (*strfrmt++) {
                case 'c': {
                    checkformat(L, form, L_FMTFLAGSC, 0);
                    nb = l_sprintf(buff, maxitem, form, (int)luaL_checkinteger(L, arg));
                    break;
                }
                case 'd':
                case 'i':
                    flags = L_FMTFLAGSI;
                    goto intcase;
                case 'u':
                    flags = L_FMTFLAGSU;
                    goto intcase;
                case 'o':
                case 'x':
                case 'X':
                    flags = L_FMTFLAGSX;
intcase: {
                        lua_Integer n = luaL_checkinteger(L, arg);
                        checkformat(L, form, flags, 1);
                        addlenmod(form, LUA_INTEGER_FRMLEN);
                        nb = l_sprintf(buff, maxitem, form, (LUAI_UACINT)n);
                        break;
                    }
                case 'a':
                case 'A':
                    checkformat(L, form, L_FMTFLAGSF, 1);
                    addlenmod(form, LUA_NUMBER_FRMLEN);
                    nb = lua_number2strx(L, buff, maxitem, form,
                                         luaL_checknumber(L, arg));
                    break;
                case 'f':
                    maxitem = MAX_ITEMF;  /* extra space for '%f' */
                    buff = luaL_prepbuffsize(&b, maxitem);
                /* FALLTHROUGH */
                case 'e':
                case 'E':
                case 'g':
                case 'G': {
                    lua_Number n = luaL_checknumber(L, arg);
                    checkformat(L, form, L_FMTFLAGSF, 1);
                    addlenmod(form, LUA_NUMBER_FRMLEN);
                    nb = l_sprintf(buff, maxitem, form, (LUAI_UACNUMBER)n);
                    break;
                }
                case 'p': {
                    const void *p = lua_topointer(L, arg);
                    checkformat(L, form, L_FMTFLAGSC, 0);
                    if (p == NULL) {  /* avoid calling 'printf' with argument NULL */
                        p = "(null)";  /* result */
                        form[strlen(form) - 1] = 's';  /* format it as a string */
                    }
                    nb = l_sprintf(buff, maxitem, form, p);
                    break;
                }
                case 'q': {
                    if (form[2] != '\0')  /* modifiers? */
                        return luaL_error(L, "specifier '%%q' cannot have modifiers");
                    addliteral(L, &b, arg);
                    break;
                }
                case 's': {
                    size_t l;
                    const char *s = luaL_tolstring(L, arg, &l);
                    if (form[2] == '\0')  /* no modifiers? */
                        luaL_addvalue(&b);  /* keep entire string */
                    else {
                        luaL_argcheck(L, l == strlen(s), arg, "string contains zeros");
                        checkformat(L, form, L_FMTFLAGSC, 1);
                        if (strchr(form, '.') == NULL && l >= 100) {
                            /* no precision and string is too long to be formatted */
                            luaL_addvalue(&b);  /* keep entire string */
                        } else { /* format the string into 'buff' */
                            nb = l_sprintf(buff, maxitem, form, s);
                            lua_pop(L, 1);  /* remove result from 'luaL_tolstring' */
                        }
                    }
                    break;
                }
                default: {  /* also treat cases 'pnLlh' */
                    return luaL_error(L, "invalid conversion '%s' to 'format'", form);
                }
            }
            lua_assert(nb < maxitem);
            luaL_addsize(&b, nb);
        }
    }
    luaL_pushresult(&b);
    return 1;
}

/* }====================================================== */


/*
** {======================================================
** PACK/UNPACK
** =======================================================
*/


/* value used for padding */
#if !defined(LUAL_PACKPADBYTE)
#define LUAL_PACKPADBYTE                0x00
#endif

/* maximum size for the binary representation of an integer */
#define MAXINTSIZE      16

/* number of bits in a character */
#define NB      CHAR_BIT

/* mask for one character (NB 1's) */
#define MC      ((1 << NB) - 1)

/* size of a lua_Integer */
#define SZINT   ((int)sizeof(lua_Integer))


/* dummy union to get native endianness */
static const union {
    int dummy;
    char little;  /* true iff machine is little endian */
} nativeendian = {1};


/*
** information to pack/unpack stuff
*/
typedef struct Header {
    lua_State *L;
    int islittle;
    int maxalign;
} Header;


/*
** options for pack/unpack
*/
typedef enum KOption {
    Kint,               /* signed integers */
    Kuint,      /* unsigned integers */
    Kfloat,     /* single-precision floating-point numbers */
    Knumber,    /* Lua "native" floating-point numbers */
    Kdouble,    /* double-precision floating-point numbers */
    Kchar,      /* fixed-length strings */
    Kstring,    /* strings with prefixed length */
    Kzstr,      /* zero-terminated strings */
    Kpadding,   /* padding */
    Kpaddalign, /* padding for alignment */
    Knop                /* no-op (configuration or spaces) */
} KOption;


/*
** Read an integer numeral from string 'fmt' or return 'df' if
** there is no numeral
*/
static int digit(int c) { return '0' <= c && c <= '9'; }

static int getnum(const char **fmt, int df) {
    if (!digit(**fmt))  /* no number? */
        return df;  /* return default value */
    else {
        int a = 0;
        do {
            a = a * 10 + (*((*fmt)++) - '0');
        } while (digit(**fmt) && a <= ((int)MAXSIZE - 9) / 10);
        return a;
    }
}


/*
** Read an integer numeral and raises an error if it is larger
** than the maximum size for integers.
*/
static int getnumlimit(Header *h, const char **fmt, int df) {
    int sz = getnum(fmt, df);
    if (l_unlikely(sz > MAXINTSIZE || sz <= 0))
        return luaL_error(h->L, "integral size (%d) out of limits [1,%d]",
                          sz, MAXINTSIZE);
    return sz;
}


/*
** Initialize Header
*/
static void initheader(lua_State *L, Header *h) {
    h->L = L;
    h->islittle = nativeendian.little;
    h->maxalign = 1;
}


/*
** Read and classify next option. 'size' is filled with option's size.
*/
static KOption getoption(Header *h, const char **fmt, int *size) {
    /* dummy structure to get native alignment requirements */
    struct cD { char c; union { LUAI_MAXALIGN; } u; };
    int opt = *((*fmt)++);
    *size = 0;  /* default */
    switch (opt) {
        case 'b':
            *size = sizeof(char);
            return Kint;
        case 'B':
            *size = sizeof(char);
            return Kuint;
        case 'h':
            *size = sizeof(short);
            return Kint;
        case 'H':
            *size = sizeof(short);
            return Kuint;
        case 'l':
            *size = sizeof(long);
            return Kint;
        case 'L':
            *size = sizeof(long);
            return Kuint;
        case 'j':
            *size = sizeof(lua_Integer);
            return Kint;
        case 'J':
            *size = sizeof(lua_Integer);
            return Kuint;
        case 'T':
            *size = sizeof(size_t);
            return Kuint;
        case 'f':
            *size = sizeof(float);
            return Kfloat;
        case 'n':
            *size = sizeof(lua_Number);
            return Knumber;
        case 'd':
            *size = sizeof(double);
            return Kdouble;
        case 'i':
            *size = getnumlimit(h, fmt, sizeof(int));
            return Kint;
        case 'I':
            *size = getnumlimit(h, fmt, sizeof(int));
            return Kuint;
        case 's':
            *size = getnumlimit(h, fmt, sizeof(size_t));
            return Kstring;
        case 'c':
            *size = getnum(fmt, -1);
            if (l_unlikely(*size == -1))
                luaL_error(h->L, "missing size for format option 'c'");
            return Kchar;
        case 'z':
            return Kzstr;
        case 'x':
            *size = 1;
            return Kpadding;
        case 'X':
            return Kpaddalign;
        case ' ':
            break;
        case '<':
            h->islittle = 1;
            break;
        case '>':
            h->islittle = 0;
            break;
        case '=':
            h->islittle = nativeendian.little;
            break;
        case '!': {
            const int maxalign = offsetof(struct cD, u);
            h->maxalign = getnumlimit(h, fmt, maxalign);
            break;
        }
        default:
            luaL_error(h->L, "invalid format option '%c'", opt);
    }
    return Knop;
}


/*
** Read, classify, and fill other details about the next option.
** 'psize' is filled with option's size, 'notoalign' with its
** alignment requirements.
** Local variable 'size' gets the size to be aligned. (Kpadal option
** always gets its full alignment, other options are limited by
** the maximum alignment ('maxalign'). Kchar option needs no alignment
** despite its size.
*/
static KOption getdetails(Header *h, size_t totalsize,
                          const char **fmt, int *psize, int *ntoalign) {
    KOption opt = getoption(h, fmt, psize);
    int align = *psize;  /* usually, alignment follows size */
    if (opt == Kpaddalign) {  /* 'X' gets alignment from following option */
        if (**fmt == '\0' || getoption(h, fmt, &align) == Kchar || align == 0)
            luaL_argerror(h->L, 1, "invalid next option for option 'X'");
    }
    if (align <= 1 || opt == Kchar)  /* need no alignment? */
        *ntoalign = 0;
    else {
        if (align > h->maxalign)  /* enforce maximum alignment */
            align = h->maxalign;
        if (l_unlikely((align & (align - 1)) != 0))  /* not a power of 2? */
            luaL_argerror(h->L, 1, "format asks for alignment not power of 2");
        *ntoalign = (align - (int)(totalsize & (align - 1))) & (align - 1);
    }
    return opt;
}


/*
** Pack integer 'n' with 'size' bytes and 'islittle' endianness.
** The final 'if' handles the case when 'size' is larger than
** the size of a Lua integer, correcting the extra sign-extension
** bytes if necessary (by default they would be zeros).
*/
static void packint(luaL_Buffer *b, lua_Unsigned n,
                    int islittle, int size, int neg) {
    char *buff = luaL_prepbuffsize(b, size);
    int i;
    buff[islittle ? 0 : size - 1] = (char)(n & MC);  /* first byte */
    for (i = 1; i < size; i++) {
        n >>= NB;
        buff[islittle ? i : size - 1 - i] = (char)(n & MC);
    }
    if (neg && size > SZINT) {  /* negative number need sign extension? */
        for (i = SZINT; i < size; i++)  /* correct extra bytes */
            buff[islittle ? i : size - 1 - i] = (char)MC;
    }
    luaL_addsize(b, size);  /* add result to buffer */
}


/*
** Copy 'size' bytes from 'src' to 'dest', correcting endianness if
** given 'islittle' is different from native endianness.
*/
static void copywithendian(char *dest, const char *src,
                           int size, int islittle) {
    if (islittle == nativeendian.little)
        memcpy(dest, src, size);
    else {
        dest += size - 1;
        while (size-- != 0)
            *(dest--) = *(src++);
    }
}


static int str_pack(lua_State *L) {
    luaL_Buffer b;
    Header h;
    const char *fmt = luaL_checkstring(L, 1);  /* format string */
    int arg = 1;  /* current argument to pack */
    size_t totalsize = 0;  /* accumulate total size of result */
    initheader(L, &h);
    lua_pushnil(L);  /* mark to separate arguments from string buffer */
    luaL_buffinit(L, &b);
    while (*fmt != '\0') {
        int size, ntoalign;
        KOption opt = getdetails(&h, totalsize, &fmt, &size, &ntoalign);
        totalsize += ntoalign + size;
        while (ntoalign-- > 0)
            luaL_addchar(&b, LUAL_PACKPADBYTE);  /* fill alignment */
        arg++;
        switch (opt) {
            case Kint: {  /* signed integers */
                lua_Integer n = luaL_checkinteger(L, arg);
                if (size < SZINT) {  /* need overflow check? */
                    lua_Integer lim = (lua_Integer)1 << ((size * NB) - 1);
                    luaL_argcheck(L, -lim <= n && n < lim, arg, "integer overflow");
                }
                packint(&b, (lua_Unsigned)n, h.islittle, size, (n < 0));
                break;
            }
            case Kuint: {  /* unsigned integers */
                lua_Integer n = luaL_checkinteger(L, arg);
                if (size < SZINT)  /* need overflow check? */
                    luaL_argcheck(L, (lua_Unsigned)n < ((lua_Unsigned)1 << (size * NB)),
                                  arg, "unsigned overflow");
                packint(&b, (lua_Unsigned)n, h.islittle, size, 0);
                break;
            }
            case Kfloat: {  /* C float */
                float f = (float)luaL_checknumber(L, arg);  /* get argument */
                char *buff = luaL_prepbuffsize(&b, sizeof(f));
                /* move 'f' to final result, correcting endianness if needed */
                copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
                luaL_addsize(&b, size);
                break;
            }
            case Knumber: {  /* Lua float */
                lua_Number f = luaL_checknumber(L, arg);  /* get argument */
                char *buff = luaL_prepbuffsize(&b, sizeof(f));
                /* move 'f' to final result, correcting endianness if needed */
                copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
                luaL_addsize(&b, size);
                break;
            }
            case Kdouble: {  /* C double */
                double f = (double)luaL_checknumber(L, arg);  /* get argument */
                char *buff = luaL_prepbuffsize(&b, sizeof(f));
                /* move 'f' to final result, correcting endianness if needed */
                copywithendian(buff, (char *)&f, sizeof(f), h.islittle);
                luaL_addsize(&b, size);
                break;
            }
            case Kchar: {  /* fixed-size string */
                size_t len;
                const char *s = luaL_checklstring(L, arg, &len);
                luaL_argcheck(L, len <= (size_t)size, arg,
                              "string longer than given size");
                luaL_addlstring(&b, s, len);  /* add string */
                while (len++ < (size_t)size)  /* pad extra space */
                    luaL_addchar(&b, LUAL_PACKPADBYTE);
                break;
            }
            case Kstring: {  /* strings with length count */
                size_t len;
                const char *s = luaL_checklstring(L, arg, &len);
                luaL_argcheck(L, size >= (int)sizeof(size_t) ||
                              len < ((size_t)1 << (size * NB)),
                              arg, "string length does not fit in given size");
                packint(&b, (lua_Unsigned)len, h.islittle, size, 0);  /* pack length */
                luaL_addlstring(&b, s, len);
                totalsize += len;
                break;
            }
            case Kzstr: {  /* zero-terminated string */
                size_t len;
                const char *s = luaL_checklstring(L, arg, &len);
                luaL_argcheck(L, strlen(s) == len, arg, "string contains zeros");
                luaL_addlstring(&b, s, len);
                luaL_addchar(&b, '\0');  /* add zero at the end */
                totalsize += len + 1;
                break;
            }
            case Kpadding:
                luaL_addchar(&b, LUAL_PACKPADBYTE);  /* FALLTHROUGH */
            case Kpaddalign:
            case Knop:
                arg--;  /* undo increment */
                break;
        }
    }
    luaL_pushresult(&b);
    return 1;
}


static int str_packsize(lua_State *L) {
    Header h;
    const char *fmt = luaL_checkstring(L, 1);  /* format string */
    size_t totalsize = 0;  /* accumulate total size of result */
    initheader(L, &h);
    while (*fmt != '\0') {
        int size, ntoalign;
        KOption opt = getdetails(&h, totalsize, &fmt, &size, &ntoalign);
        luaL_argcheck(L, opt != Kstring && opt != Kzstr, 1,
                      "variable-length format");
        size += ntoalign;  /* total space used by option */
        luaL_argcheck(L, totalsize <= MAXSIZE - size, 1,
                      "format result too large");
        totalsize += size;
    }
    lua_pushinteger(L, (lua_Integer)totalsize);
    return 1;
}


/*
** Unpack an integer with 'size' bytes and 'islittle' endianness.
** If size is smaller than the size of a Lua integer and integer
** is signed, must do sign extension (propagating the sign to the
** higher bits); if size is larger than the size of a Lua integer,
** it must check the unread bytes to see whether they do not cause an
** overflow.
*/
static lua_Integer unpackint(lua_State *L, const char *str,
                             int islittle, int size, int issigned) {
    lua_Unsigned res = 0;
    int i;
    int limit = (size  <= SZINT) ? size : SZINT;
    for (i = limit - 1; i >= 0; i--) {
        res <<= NB;
        res |= (lua_Unsigned)(unsigned char)str[islittle ? i : size - 1 - i];
    }
    if (size < SZINT) {  /* real size smaller than lua_Integer? */
        if (issigned) {  /* needs sign extension? */
            lua_Unsigned mask = (lua_Unsigned)1 << (size * NB - 1);
            res = ((res ^ mask) - mask);  /* do sign extension */
        }
    } else if (size > SZINT) { /* must check unread bytes */
        int mask = (!issigned || (lua_Integer)res >= 0) ? 0 : MC;
        for (i = limit; i < size; i++) {
            if (l_unlikely((unsigned char)str[islittle ? i : size - 1 - i] != mask))
                luaL_error(L, "%d-byte integer does not fit into Lua Integer", size);
        }
    }
    return (lua_Integer)res;
}


static int str_unpack(lua_State *L) {
    Header h;
    const char *fmt = luaL_checkstring(L, 1);
    size_t ld;
    const char *data = luaL_checklstring(L, 2, &ld);
    size_t pos = posrelatI(luaL_optinteger(L, 3, 1), ld) - 1;
    int n = 0;  /* number of results */
    luaL_argcheck(L, pos <= ld, 3, "initial position out of string");
    initheader(L, &h);
    while (*fmt != '\0') {
        int size, ntoalign;
        KOption opt = getdetails(&h, pos, &fmt, &size, &ntoalign);
        luaL_argcheck(L, (size_t)ntoalign + size <= ld - pos, 2,
                      "data string too short");
        pos += ntoalign;  /* skip alignment */
        /* stack space for item + next position */
        luaL_checkstack(L, 2, "too many results");
        n++;
        switch (opt) {
            case Kint:
            case Kuint: {
                lua_Integer res = unpackint(L, data + pos, h.islittle, size,
                                            (opt == Kint));
                lua_pushinteger(L, res);
                break;
            }
            case Kfloat: {
                float f;
                copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
                lua_pushnumber(L, (lua_Number)f);
                break;
            }
            case Knumber: {
                lua_Number f;
                copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
                lua_pushnumber(L, f);
                break;
            }
            case Kdouble: {
                double f;
                copywithendian((char *)&f, data + pos, sizeof(f), h.islittle);
                lua_pushnumber(L, (lua_Number)f);
                break;
            }
            case Kchar: {
                lua_pushlstring(L, data + pos, size);
                break;
            }
            case Kstring: {
                size_t len = (size_t)unpackint(L, data + pos, h.islittle, size, 0);
                luaL_argcheck(L, len <= ld - pos - size, 2, "data string too short");
                lua_pushlstring(L, data + pos + size, len);
                pos += len;  /* skip string */
                break;
            }
            case Kzstr: {
                size_t len = strlen(data + pos);
                luaL_argcheck(L, pos + len < ld, 2,
                              "unfinished string for format 'z'");
                lua_pushlstring(L, data + pos, len);
                pos += len + 1;  /* skip string plus final '\0' */
                break;
            }
            case Kpaddalign:
            case Kpadding:
            case Knop:
                n--;  /* undo increment */
                break;
        }
        pos += size;
    }
    lua_pushinteger(L, pos + 1);  /* next position */
    return n + 1;
}

/* }====================================================== */


static const luaL_Reg strlib[] = {
    {"byte", str_byte},
    {"char", str_char},
    {"dump", str_dump},
    {"find", str_find},
    {"format", str_format},
    {"gmatch", gmatch},
    {"gsub", str_gsub},
    {"len", str_len},
    {"lower", str_lower},
    {"match", str_match},
    {"rep", str_rep},
    {"reverse", str_reverse},
    {"sub", str_sub},
    {"upper", str_upper},
    {"pack", str_pack},
    {"packsize", str_packsize},
    {"unpack", str_unpack},
    {NULL, NULL}
};


static void createmetatable(lua_State *L) {
    /* table to be metatable for strings */
    luaL_newlibtable(L, stringmetamethods);
    luaL_setfuncs(L, stringmetamethods, 0);
    lua_pushliteral(L, "");  /* dummy string */
    lua_pushvalue(L, -2);  /* copy table */
    lua_setmetatable(L, -2);  /* set table as metatable for strings */
    lua_pop(L, 1);  /* pop dummy string */
    lua_pushvalue(L, -2);  /* get string library */
    lua_setfield(L, -2, "__index");  /* metatable.__index = string */
    lua_pop(L, 1);  /* pop metatable */
}


/*
** Open string library
*/
LUAMOD_API int luaopen_string(lua_State *L) {
    luaL_newlib(L, strlib);
    createmetatable(L);
    return 1;
}