common/dist/zlib/inffast.c

   1 /*      $NetBSD: inffast.c,v 1.3 2006/01/27 00:45:27 christos Exp $     */
   2
   3 /* inffast.c -- fast decoding
   4  * Copyright (C) 1995-2004 Mark Adler
   5  * For conditions of distribution and use, see copyright notice in zlib.h
   6  */
   7
   8 #include "zutil.h"
   9 #include "inftrees.h"
  10 #include "inflate.h"
  11 #include "inffast.h"
  12
  13 #ifndef ASMINF
  14
  15 /* Allow machine dependent optimization for post-increment or pre-increment.
  16    Based on testing to date,
  17    Pre-increment preferred for:
  18    - PowerPC G3 (Adler)
  19    - MIPS R5000 (Randers-Pehrson)
  20    Post-increment preferred for:
  21    - none
  22    No measurable difference:
  23    - Pentium III (Anderson)
  24    - M68060 (Nikl)
  25  */
  26 #ifdef POSTINC
  27 #  define OFF 0
  28 #  define PUP(a) *(a)++
  29 #else
  30 #  define OFF 1
  31 #  define PUP(a) *++(a)
  32 #endif
  33
  34 /*
  35    Decode literal, length, and distance codes and write out the resulting
  36    literal and match bytes until either not enough input or output is
  37    available, an end-of-block is encountered, or a data error is encountered.
  38    When large enough input and output buffers are supplied to inflate(), for
  39    example, a 16K input buffer and a 64K output buffer, more than 95% of the
  40    inflate execution time is spent in this routine.
  41
  42    Entry assumptions:
  43
  44         state->mode == LEN
  45         strm->avail_in >= 6
  46         strm->avail_out >= 258
  47         start >= strm->avail_out
  48         state->bits < 8
  49
  50    On return, state->mode is one of:
  51
  52         LEN -- ran out of enough output space or enough available input
  53         TYPE -- reached end of block code, inflate() to interpret next block
  54         BAD -- error in block data
  55
  56    Notes:
  57
  58     - The maximum input bits used by a length/distance pair is 15 bits for the
  59       length code, 5 bits for the length extra, 15 bits for the distance code,
  60       and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
  61       Therefore if strm->avail_in >= 6, then there is enough input to avoid
  62       checking for available input while decoding.
  63
  64     - The maximum bytes that a single length/distance pair can output is 258
  65       bytes, which is the maximum length that can be coded.  inflate_fast()
  66       requires strm->avail_out >= 258 for each loop to avoid checking for
  67       output space.
  68  */
  69 void inflate_fast(strm, start)
  70 z_streamp strm;
  71 unsigned start;         /* inflate()'s starting value for strm->avail_out */
  72 {
  73     struct inflate_state FAR *state;
  74     unsigned char FAR *in;      /* local strm->next_in */
  75     unsigned char FAR *last;    /* while in < last, enough input available */
  76     unsigned char FAR *out;     /* local strm->next_out */
  77     unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
  78     unsigned char FAR *end;     /* while out < end, enough space available */
  79 #ifdef INFLATE_STRICT
  80     unsigned dmax;              /* maximum distance from zlib header */
  81 #endif
  82     unsigned wsize;             /* window size or zero if not using window */
  83     unsigned whave;             /* valid bytes in the window */
  84     unsigned wwrite;            /* window write index */
  85     unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
  86     unsigned long hold;         /* local strm->hold */
  87     unsigned bits;              /* local strm->bits */
  88     code const FAR *lcode;      /* local strm->lencode */
  89     code const FAR *dcode;      /* local strm->distcode */
  90     unsigned lmask;             /* mask for first level of length codes */
  91     unsigned dmask;             /* mask for first level of distance codes */
  92     code this;                  /* retrieved table entry */
  93     unsigned op;                /* code bits, operation, extra bits, or */
  94                                 /*  window position, window bytes to copy */
  95     unsigned len;               /* match length, unused bytes */
  96     unsigned dist;              /* match distance */
  97     unsigned char FAR *from;    /* where to copy match from */
  98
  99     /* copy state to local variables */
 100     state = (struct inflate_state FAR *)strm->state;
 101     in = strm->next_in - OFF;
 102     last = in + (strm->avail_in - 5);
 103     out = strm->next_out - OFF;
 104     beg = out - (start - strm->avail_out);
 105     end = out + (strm->avail_out - 257);
 106 #ifdef INFLATE_STRICT
 107     dmax = state->dmax;
 108 #endif
 109     wsize = state->wsize;
 110     whave = state->whave;
 111     wwrite = state->write;
 112     window = state->window;
 113     hold = state->hold;
 114     bits = state->bits;
 115     lcode = state->lencode;
 116     dcode = state->distcode;
 117     lmask = (1U << state->lenbits) - 1;
 118     dmask = (1U << state->distbits) - 1;
 119
 120     /* decode literals and length/distances until end-of-block or not enough
 121        input data or output space */
 122     do {
 123         if (bits < 15) {
 124             hold += (unsigned long)(PUP(in)) << bits;
 125             bits += 8;
 126             hold += (unsigned long)(PUP(in)) << bits;
 127             bits += 8;
 128         }
 129         this = lcode[hold & lmask];
 130       dolen:
 131         op = (unsigned)(this.bits);
 132         hold >>= op;
 133         bits -= op;
 134         op = (unsigned)(this.op);
 135         if (op == 0) {                          /* literal */
 136             Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
 137                     "inflate:         literal '%c'\n" :
 138                     "inflate:         literal 0x%02x\n", this.val));
 139             PUP(out) = (unsigned char)(this.val);
 140         }
 141         else if (op & 16) {                     /* length base */
 142             len = (unsigned)(this.val);
 143             op &= 15;                           /* number of extra bits */
 144             if (op) {
 145                 if (bits < op) {
 146                     hold += (unsigned long)(PUP(in)) << bits;
 147                     bits += 8;
 148                 }
 149                 len += (unsigned)hold & ((1U << op) - 1);
 150                 hold >>= op;
 151                 bits -= op;
 152             }
 153             Tracevv((stderr, "inflate:         length %u\n", len));
 154             if (bits < 15) {
 155                 hold += (unsigned long)(PUP(in)) << bits;
 156                 bits += 8;
 157                 hold += (unsigned long)(PUP(in)) << bits;
 158                 bits += 8;
 159             }
 160             this = dcode[hold & dmask];
 161           dodist:
 162             op = (unsigned)(this.bits);
 163             hold >>= op;
 164             bits -= op;
 165             op = (unsigned)(this.op);
 166             if (op & 16) {                      /* distance base */
 167                 dist = (unsigned)(this.val);
 168                 op &= 15;                       /* number of extra bits */
 169                 if (bits < op) {
 170                     hold += (unsigned long)(PUP(in)) << bits;
 171                     bits += 8;
 172                     if (bits < op) {
 173                         hold += (unsigned long)(PUP(in)) << bits;
 174                         bits += 8;
 175                     }
 176                 }
 177                 dist += (unsigned)hold & ((1U << op) - 1);
 178 #ifdef INFLATE_STRICT
 179                 if (dist > dmax) {
 180                     strm->msg = (char *)"invalid distance too far back";
 181                     state->mode = BAD;
 182                     break;
 183                 }
 184 #endif
 185                 hold >>= op;
 186                 bits -= op;
 187                 Tracevv((stderr, "inflate:         distance %u\n", dist));
 188                 op = (unsigned)(out - beg);     /* max distance in output */
 189                 if (dist > op) {                /* see if copy from window */
 190                     op = dist - op;             /* distance back in window */
 191                     if (op > whave) {
 192                         strm->msg = __UNCONST("invalid distance too far back");
 193                         state->mode = BAD;
 194                         break;
 195                     }
 196                     from = window - OFF;
 197                     if (wwrite == 0) {           /* very common case */
 198                         from += wsize - op;
 199                         if (op < len) {         /* some from window */
 200                             len -= op;
 201                             do {
 202                                 PUP(out) = PUP(from);
 203                             } while (--op);
 204                             from = out - dist;  /* rest from output */
 205                         }
 206                     }
 207                     else if (wwrite < op) {      /* wrap around window */
 208                         from += wsize + wwrite - op;
 209                         op -= wwrite;
 210                         if (op < len) {         /* some from end of window */
 211                             len -= op;
 212                             do {
 213                                 PUP(out) = PUP(from);
 214                             } while (--op);
 215                             from = window - OFF;
 216                             if (wwrite < len) {  /* some from start of window */
 217                                 op = wwrite;
 218                                 len -= op;
 219                                 do {
 220                                     PUP(out) = PUP(from);
 221                                 } while (--op);
 222                                 from = out - dist;      /* rest from output */
 223                             }
 224                         }
 225                     }
 226                     else {                      /* contiguous in window */
 227                         from += wwrite - op;
 228                         if (op < len) {         /* some from window */
 229                             len -= op;
 230                             do {
 231                                 PUP(out) = PUP(from);
 232                             } while (--op);
 233                             from = out - dist;  /* rest from output */
 234                         }
 235                     }
 236                     while (len > 2) {
 237                         PUP(out) = PUP(from);
 238                         PUP(out) = PUP(from);
 239                         PUP(out) = PUP(from);
 240                         len -= 3;
 241                     }
 242                     if (len) {
 243                         PUP(out) = PUP(from);
 244                         if (len > 1)
 245                             PUP(out) = PUP(from);
 246                     }
 247                 }
 248                 else {
 249                     from = out - dist;          /* copy direct from output */
 250                     do {                        /* minimum length is three */
 251                         PUP(out) = PUP(from);
 252                         PUP(out) = PUP(from);
 253                         PUP(out) = PUP(from);
 254                         len -= 3;
 255                     } while (len > 2);
 256                     if (len) {
 257                         PUP(out) = PUP(from);
 258                         if (len > 1)
 259                             PUP(out) = PUP(from);
 260                     }
 261                 }
 262             }
 263             else if ((op & 64) == 0) {          /* 2nd level distance code */
 264                 this = dcode[this.val + (hold & ((1U << op) - 1))];
 265                 goto dodist;
 266             }
 267             else {
 268                 strm->msg = __UNCONST("invalid distance code");
 269                 state->mode = BAD;
 270                 break;
 271             }
 272         }
 273         else if ((op & 64) == 0) {              /* 2nd level length code */
 274             this = lcode[this.val + (hold & ((1U << op) - 1))];
 275             goto dolen;
 276         }
 277         else if (op & 32) {                     /* end-of-block */
 278             Tracevv((stderr, "inflate:         end of block\n"));
 279             state->mode = TYPE;
 280             break;
 281         }
 282         else {
 283             strm->msg = __UNCONST("invalid literal/length code");
 284             state->mode = BAD;
 285             break;
 286         }
 287     } while (in < last && out < end);
 288
 289     /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
 290     len = bits >> 3;
 291     in -= len;
 292     bits -= len << 3;
 293     hold &= (1U << bits) - 1;
 294
 295     /* update state and return */
 296     strm->next_in = in + OFF;
 297     strm->next_out = out + OFF;
 298     strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
 299     strm->avail_out = (unsigned)(out < end ?
 300                                  257 + (end - out) : 257 - (out - end));
 301     state->hold = hold;
 302     state->bits = bits;
 303     return;
 304 }
 305
 306 /*
 307    inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
 308    - Using bit fields for code structure
 309    - Different op definition to avoid & for extra bits (do & for table bits)
 310    - Three separate decoding do-loops for direct, window, and write == 0
 311    - Special case for distance > 1 copies to do overlapped load and store copy
 312    - Explicit branch predictions (based on measured branch probabilities)
 313    - Deferring match copy and interspersed it with decoding subsequent codes
 314    - Swapping literal/length else
 315    - Swapping window/direct else
 316    - Larger unrolled copy loops (three is about right)
 317    - Moving len -= 3 statement into middle of loop
 318  */
 319
 320 #endif /* !ASMINF */