liblua/lbitlib.c

   1 /*
   2 ** $Id: lbitlib.c,v 1.18 2013/03/19 13:19:12 roberto Exp $
   3 ** Standard library for bitwise operations
   4 ** See Copyright Notice in lua.h
   5 */
   6
   7 #define lbitlib_c
   8 #define LUA_LIB
   9
  10 #include "lua.h"
  11
  12 #include "lauxlib.h"
  13 #include "lualib.h"
  14
  15
  16 /* number of bits to consider in a number */
  17 #if !defined(LUA_NBITS)
  18 #define LUA_NBITS       32
  19 #endif
  20
  21
  22 #define ALLONES         (~(((~(lua_Unsigned)0) << (LUA_NBITS - 1)) << 1))
  23
  24 /* macro to trim extra bits */
  25 #define trim(x)         ((x) & ALLONES)
  26
  27
  28 /* builds a number with 'n' ones (1 <= n <= LUA_NBITS) */
  29 #define mask(n)         (~((ALLONES << 1) << ((n) - 1)))
  30
  31
  32 typedef lua_Unsigned b_uint;
  33
  34
  35
  36 static b_uint andaux (lua_State *L) {
  37   int i, n = lua_gettop(L);
  38   b_uint r = ~(b_uint)0;
  39   for (i = 1; i <= n; i++)
  40     r &= luaL_checkunsigned(L, i);
  41   return trim(r);
  42 }
  43
  44
  45 static int b_and (lua_State *L) {
  46   b_uint r = andaux(L);
  47   lua_pushunsigned(L, r);
  48   return 1;
  49 }
  50
  51
  52 static int b_test (lua_State *L) {
  53   b_uint r = andaux(L);
  54   lua_pushboolean(L, r != 0);
  55   return 1;
  56 }
  57
  58
  59 static int b_or (lua_State *L) {
  60   int i, n = lua_gettop(L);
  61   b_uint r = 0;
  62   for (i = 1; i <= n; i++)
  63     r |= luaL_checkunsigned(L, i);
  64   lua_pushunsigned(L, trim(r));
  65   return 1;
  66 }
  67
  68
  69 static int b_xor (lua_State *L) {
  70   int i, n = lua_gettop(L);
  71   b_uint r = 0;
  72   for (i = 1; i <= n; i++)
  73     r ^= luaL_checkunsigned(L, i);
  74   lua_pushunsigned(L, trim(r));
  75   return 1;
  76 }
  77
  78
  79 static int b_not (lua_State *L) {
  80   b_uint r = ~luaL_checkunsigned(L, 1);
  81   lua_pushunsigned(L, trim(r));
  82   return 1;
  83 }
  84
  85
  86 static int b_shift (lua_State *L, b_uint r, int i) {
  87   if (i < 0) {  /* shift right? */
  88     i = -i;
  89     r = trim(r);
  90     if (i >= LUA_NBITS) r = 0;
  91     else r >>= i;
  92   }
  93   else {  /* shift left */
  94     if (i >= LUA_NBITS) r = 0;
  95     else r <<= i;
  96     r = trim(r);
  97   }
  98   lua_pushunsigned(L, r);
  99   return 1;
 100 }
 101
 102
 103 static int b_lshift (lua_State *L) {
 104   return b_shift(L, luaL_checkunsigned(L, 1), luaL_checkint(L, 2));
 105 }
 106
 107
 108 static int b_rshift (lua_State *L) {
 109   return b_shift(L, luaL_checkunsigned(L, 1), -luaL_checkint(L, 2));
 110 }
 111
 112
 113 static int b_arshift (lua_State *L) {
 114   b_uint r = luaL_checkunsigned(L, 1);
 115   int i = luaL_checkint(L, 2);
 116   if (i < 0 || !(r & ((b_uint)1 << (LUA_NBITS - 1))))
 117     return b_shift(L, r, -i);
 118   else {  /* arithmetic shift for 'negative' number */
 119     if (i >= LUA_NBITS) r = ALLONES;
 120     else
 121       r = trim((r >> i) | ~(~(b_uint)0 >> i));  /* add signal bit */
 122     lua_pushunsigned(L, r);
 123     return 1;
 124   }
 125 }
 126
 127
 128 static int b_rot (lua_State *L, int i) {
 129   b_uint r = luaL_checkunsigned(L, 1);
 130   i &= (LUA_NBITS - 1);  /* i = i % NBITS */
 131   r = trim(r);
 132   r = (r << i) | (r >> (LUA_NBITS - i));
 133   lua_pushunsigned(L, trim(r));
 134   return 1;
 135 }
 136
 137
 138 static int b_lrot (lua_State *L) {
 139   return b_rot(L, luaL_checkint(L, 2));
 140 }
 141
 142
 143 static int b_rrot (lua_State *L) {
 144   return b_rot(L, -luaL_checkint(L, 2));
 145 }
 146
 147
 148 /*
 149 ** get field and width arguments for field-manipulation functions,
 150 ** checking whether they are valid.
 151 ** ('luaL_error' called without 'return' to avoid later warnings about
 152 ** 'width' being used uninitialized.)
 153 */
 154 static int fieldargs (lua_State *L, int farg, int *width) {
 155   int f = luaL_checkint(L, farg);
 156   int w = luaL_optint(L, farg + 1, 1);
 157   luaL_argcheck(L, 0 <= f, farg, "field cannot be negative");
 158   luaL_argcheck(L, 0 < w, farg + 1, "width must be positive");
 159   if (f + w > LUA_NBITS)
 160     luaL_error(L, "trying to access non-existent bits");
 161   *width = w;
 162   return f;
 163 }
 164
 165
 166 static int b_extract (lua_State *L) {
 167   int w;
 168   b_uint r = luaL_checkunsigned(L, 1);
 169   int f = fieldargs(L, 2, &w);
 170   r = (r >> f) & mask(w);
 171   lua_pushunsigned(L, r);
 172   return 1;
 173 }
 174
 175
 176 static int b_replace (lua_State *L) {
 177   int w;
 178   b_uint r = luaL_checkunsigned(L, 1);
 179   b_uint v = luaL_checkunsigned(L, 2);
 180   int f = fieldargs(L, 3, &w);
 181   int m = mask(w);
 182   v &= m;  /* erase bits outside given width */
 183   r = (r & ~(m << f)) | (v << f);
 184   lua_pushunsigned(L, r);
 185   return 1;
 186 }
 187
 188
 189 static const luaL_Reg bitlib[] = {
 190   {"arshift", b_arshift},
 191   {"band", b_and},
 192   {"bnot", b_not},
 193   {"bor", b_or},
 194   {"bxor", b_xor},
 195   {"btest", b_test},
 196   {"extract", b_extract},
 197   {"lrotate", b_lrot},
 198   {"lshift", b_lshift},
 199   {"replace", b_replace},
 200   {"rrotate", b_rrot},
 201   {"rshift", b_rshift},
 202   {NULL, NULL}
 203 };
 204
 205
 206
 207 LUAMOD_API int luaopen_bit32 (lua_State *L) {
 208   luaL_newlib(L, bitlib);
 209   return 1;
 210 }
 211