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1.8.7

    1: /* inffast.c -- fast decoding
    2:  * Copyright (C) 1995-2008, 2010 Mark Adler
    3:  * For conditions of distribution and use, see copyright notice in zlib.h
    4:  */
    5: 
    6: #include "zutil.h"
    7: #include "inftrees.h"
    8: #include "inflate.h"
    9: #include "inffast.h"
   10: 
   11: #ifndef ASMINF
   12: 
   13: /* Allow machine dependent optimization for post-increment or pre-increment.
   14:    Based on testing to date,
   15:    Pre-increment preferred for:
   16:    - PowerPC G3 (Adler)
   17:    - MIPS R5000 (Randers-Pehrson)
   18:    Post-increment preferred for:
   19:    - none
   20:    No measurable difference:
   21:    - Pentium III (Anderson)
   22:    - M68060 (Nikl)
   23:  */
   24: #ifdef POSTINC
   25: #  define OFF 0
   26: #  define PUP(a) *(a)++
   27: #else
   28: #  define OFF 1
   29: #  define PUP(a) *++(a)
   30: #endif
   31: 
   32: /*
   33:    Decode literal, length, and distance codes and write out the resulting
   34:    literal and match bytes until either not enough input or output is
   35:    available, an end-of-block is encountered, or a data error is encountered.
   36:    When large enough input and output buffers are supplied to inflate(), for
   37:    example, a 16K input buffer and a 64K output buffer, more than 95% of the
   38:    inflate execution time is spent in this routine.
   39: 
   40:    Entry assumptions:
   41: 
   42:         state->mode == LEN
   43:         strm->avail_in >= 6
   44:         strm->avail_out >= 258
   45:         start >= strm->avail_out
   46:         state->bits < 8
   47: 
   48:    On return, state->mode is one of:
   49: 
   50:         LEN -- ran out of enough output space or enough available input
   51:         TYPE -- reached end of block code, inflate() to interpret next block
   52:         BAD -- error in block data
   53: 
   54:    Notes:
   55: 
   56:     - The maximum input bits used by a length/distance pair is 15 bits for the
   57:       length code, 5 bits for the length extra, 15 bits for the distance code,
   58:       and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
   59:       Therefore if strm->avail_in >= 6, then there is enough input to avoid
   60:       checking for available input while decoding.
   61: 
   62:     - The maximum bytes that a single length/distance pair can output is 258
   63:       bytes, which is the maximum length that can be coded.  inflate_fast()
   64:       requires strm->avail_out >= 258 for each loop to avoid checking for
   65:       output space.
   66:  */
   67: void ZLIB_INTERNAL inflate_fast(strm, start)
   68: z_streamp strm;
   69: unsigned start;         /* inflate()'s starting value for strm->avail_out */
   70: {
   71:     struct inflate_state FAR *state;
   72:     unsigned char FAR *in;      /* local strm->next_in */
   73:     unsigned char FAR *last;    /* while in < last, enough input available */
   74:     unsigned char FAR *out;     /* local strm->next_out */
   75:     unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
   76:     unsigned char FAR *end;     /* while out < end, enough space available */
   77: #ifdef INFLATE_STRICT
   78:     unsigned dmax;              /* maximum distance from zlib header */
   79: #endif
   80:     unsigned wsize;             /* window size or zero if not using window */
   81:     unsigned whave;             /* valid bytes in the window */
   82:     unsigned wnext;             /* window write index */
   83:     unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
   84:     unsigned long hold;         /* local strm->hold */
   85:     unsigned bits;              /* local strm->bits */
   86:     code const FAR *lcode;      /* local strm->lencode */
   87:     code const FAR *dcode;      /* local strm->distcode */
   88:     unsigned lmask;             /* mask for first level of length codes */
   89:     unsigned dmask;             /* mask for first level of distance codes */
   90:     code here;                  /* retrieved table entry */
   91:     unsigned op;                /* code bits, operation, extra bits, or */
   92:                                 /*  window position, window bytes to copy */
   93:     unsigned len;               /* match length, unused bytes */
   94:     unsigned dist;              /* match distance */
   95:     unsigned char FAR *from;    /* where to copy match from */
   96: 
   97:     /* copy state to local variables */
   98:     state = (struct inflate_state FAR *)strm->state;
   99:     in = strm->next_in - OFF;
  100:     last = in + (strm->avail_in - 5);
  101:     out = strm->next_out - OFF;
  102:     beg = out - (start - strm->avail_out);
  103:     end = out + (strm->avail_out - 257);
  104: #ifdef INFLATE_STRICT
  105:     dmax = state->dmax;
  106: #endif
  107:     wsize = state->wsize;
  108:     whave = state->whave;
  109:     wnext = state->wnext;
  110:     window = state->window;
  111:     hold = state->hold;
  112:     bits = state->bits;
  113:     lcode = state->lencode;
  114:     dcode = state->distcode;
  115:     lmask = (1U << state->lenbits) - 1;
  116:     dmask = (1U << state->distbits) - 1;
  117: 
  118:     /* decode literals and length/distances until end-of-block or not enough
  119:        input data or output space */
  120:     do {
  121:         if (bits < 15) {
  122:             hold += (unsigned long)(PUP(in)) << bits;
  123:             bits += 8;
  124:             hold += (unsigned long)(PUP(in)) << bits;
  125:             bits += 8;
  126:         }
  127:         here = lcode[hold & lmask];
  128:       dolen:
  129:         op = (unsigned)(here.bits);
  130:         hold >>= op;
  131:         bits -= op;
  132:         op = (unsigned)(here.op);
  133:         if (op == 0) {                          /* literal */
  134:             Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
  135:                     "inflate:         literal '%c'\n" :
  136:                     "inflate:         literal 0x%02x\n", here.val));
  137:             PUP(out) = (unsigned char)(here.val);
  138:         }
  139:         else if (op & 16) {                     /* length base */
  140:             len = (unsigned)(here.val);
  141:             op &= 15;                           /* number of extra bits */
  142:             if (op) {
  143:                 if (bits < op) {
  144:                     hold += (unsigned long)(PUP(in)) << bits;
  145:                     bits += 8;
  146:                 }
  147:                 len += (unsigned)hold & ((1U << op) - 1);
  148:                 hold >>= op;
  149:                 bits -= op;
  150:             }
  151:             Tracevv((stderr, "inflate:         length %u\n", len));
  152:             if (bits < 15) {
  153:                 hold += (unsigned long)(PUP(in)) << bits;
  154:                 bits += 8;
  155:                 hold += (unsigned long)(PUP(in)) << bits;
  156:                 bits += 8;
  157:             }
  158:             here = dcode[hold & dmask];
  159:           dodist:
  160:             op = (unsigned)(here.bits);
  161:             hold >>= op;
  162:             bits -= op;
  163:             op = (unsigned)(here.op);
  164:             if (op & 16) {                      /* distance base */
  165:                 dist = (unsigned)(here.val);
  166:                 op &= 15;                       /* number of extra bits */
  167:                 if (bits < op) {
  168:                     hold += (unsigned long)(PUP(in)) << bits;
  169:                     bits += 8;
  170:                     if (bits < op) {
  171:                         hold += (unsigned long)(PUP(in)) << bits;
  172:                         bits += 8;
  173:                     }
  174:                 }
  175:                 dist += (unsigned)hold & ((1U << op) - 1);
  176: #ifdef INFLATE_STRICT
  177:                 if (dist > dmax) {
  178:                     strm->msg = (char *)"invalid distance too far back";
  179:                     state->mode = BAD;
  180:                     break;
  181:                 }
  182: #endif
  183:                 hold >>= op;
  184:                 bits -= op;
  185:                 Tracevv((stderr, "inflate:         distance %u\n", dist));
  186:                 op = (unsigned)(out - beg);     /* max distance in output */
  187:                 if (dist > op) {                /* see if copy from window */
  188:                     op = dist - op;             /* distance back in window */
  189:                     if (op > whave) {
  190:                         if (state->sane) {
  191:                             strm->msg =
  192:                                 (char *)"invalid distance too far back";
  193:                             state->mode = BAD;
  194:                             break;
  195:                         }
  196: #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
  197:                         if (len <= op - whave) {
  198:                             do {
  199:                                 PUP(out) = 0;
  200:                             } while (--len);
  201:                             continue;
  202:                         }
  203:                         len -= op - whave;
  204:                         do {
  205:                             PUP(out) = 0;
  206:                         } while (--op > whave);
  207:                         if (op == 0) {
  208:                             from = out - dist;
  209:                             do {
  210:                                 PUP(out) = PUP(from);
  211:                             } while (--len);
  212:                             continue;
  213:                         }
  214: #endif
  215:                     }
  216:                     from = window - OFF;
  217:                     if (wnext == 0) {           /* very common case */
  218:                         from += wsize - op;
  219:                         if (op < len) {         /* some from window */
  220:                             len -= op;
  221:                             do {
  222:                                 PUP(out) = PUP(from);
  223:                             } while (--op);
  224:                             from = out - dist;  /* rest from output */
  225:                         }
  226:                     }
  227:                     else if (wnext < op) {      /* wrap around window */
  228:                         from += wsize + wnext - op;
  229:                         op -= wnext;
  230:                         if (op < len) {         /* some from end of window */
  231:                             len -= op;
  232:                             do {
  233:                                 PUP(out) = PUP(from);
  234:                             } while (--op);
  235:                             from = window - OFF;
  236:                             if (wnext < len) {  /* some from start of window */
  237:                                 op = wnext;
  238:                                 len -= op;
  239:                                 do {
  240:                                     PUP(out) = PUP(from);
  241:                                 } while (--op);
  242:                                 from = out - dist;      /* rest from output */
  243:                             }
  244:                         }
  245:                     }
  246:                     else {                      /* contiguous in window */
  247:                         from += wnext - op;
  248:                         if (op < len) {         /* some from window */
  249:                             len -= op;
  250:                             do {
  251:                                 PUP(out) = PUP(from);
  252:                             } while (--op);
  253:                             from = out - dist;  /* rest from output */
  254:                         }
  255:                     }
  256:                     while (len > 2) {
  257:                         PUP(out) = PUP(from);
  258:                         PUP(out) = PUP(from);
  259:                         PUP(out) = PUP(from);
  260:                         len -= 3;
  261:                     }
  262:                     if (len) {
  263:                         PUP(out) = PUP(from);
  264:                         if (len > 1)
  265:                             PUP(out) = PUP(from);
  266:                     }
  267:                 }
  268:                 else {
  269:                     from = out - dist;          /* copy direct from output */
  270:                     do {                        /* minimum length is three */
  271:                         PUP(out) = PUP(from);
  272:                         PUP(out) = PUP(from);
  273:                         PUP(out) = PUP(from);
  274:                         len -= 3;
  275:                     } while (len > 2);
  276:                     if (len) {
  277:                         PUP(out) = PUP(from);
  278:                         if (len > 1)
  279:                             PUP(out) = PUP(from);
  280:                     }
  281:                 }
  282:             }
  283:             else if ((op & 64) == 0) {          /* 2nd level distance code */
  284:                 here = dcode[here.val + (hold & ((1U << op) - 1))];
  285:                 goto dodist;
  286:             }
  287:             else {
  288:                 strm->msg = (char *)"invalid distance code";
  289:                 state->mode = BAD;
  290:                 break;
  291:             }
  292:         }
  293:         else if ((op & 64) == 0) {              /* 2nd level length code */
  294:             here = lcode[here.val + (hold & ((1U << op) - 1))];
  295:             goto dolen;
  296:         }
  297:         else if (op & 32) {                     /* end-of-block */
  298:             Tracevv((stderr, "inflate:         end of block\n"));
  299:             state->mode = TYPE;
  300:             break;
  301:         }
  302:         else {
  303:             strm->msg = (char *)"invalid literal/length code";
  304:             state->mode = BAD;
  305:             break;
  306:         }
  307:     } while (in < last && out < end);
  308: 
  309:     /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
  310:     len = bits >> 3;
  311:     in -= len;
  312:     bits -= len << 3;
  313:     hold &= (1U << bits) - 1;
  314: 
  315:     /* update state and return */
  316:     strm->next_in = in + OFF;
  317:     strm->next_out = out + OFF;
  318:     strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
  319:     strm->avail_out = (unsigned)(out < end ?
  320:                                  257 + (end - out) : 257 - (out - end));
  321:     state->hold = hold;
  322:     state->bits = bits;
  323:     return;
  324: }
  325: 
  326: /*
  327:    inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
  328:    - Using bit fields for code structure
  329:    - Different op definition to avoid & for extra bits (do & for table bits)
  330:    - Three separate decoding do-loops for direct, window, and wnext == 0
  331:    - Special case for distance > 1 copies to do overlapped load and store copy
  332:    - Explicit branch predictions (based on measured branch probabilities)
  333:    - Deferring match copy and interspersed it with decoding subsequent codes
  334:    - Swapping literal/length else
  335:    - Swapping window/direct else
  336:    - Larger unrolled copy loops (three is about right)
  337:    - Moving len -= 3 statement into middle of loop
  338:  */
  339: 
  340: #endif /* !ASMINF */