File indexing completed on 2024-04-21 11:22:11

 /* inffast.c -- fast decoding
  * Copyright (C) 1995-2008, 2010, 2013 Mark Adler
  * For conditions of distribution and use, see copyright notice in zlib.h
  */
 
 #include "zutil.h"
 #include "inftrees.h"
 #include "inflate.h"
 #include "inffast.h"
 
 #ifndef ASMINF
 
 /* Allow machine dependent optimization for post-increment or pre-increment.
    Based on testing to date,
    Pre-increment preferred for:
    - PowerPC G3 (Adler)
    - MIPS R5000 (Randers-Pehrson)
    Post-increment preferred for:
    - none
    No measurable difference:
    - Pentium III (Anderson)
    - M68060 (Nikl)
  */
 #ifdef POSTINC
 #  define OFF 0
 #  define PUP(a) *(a)++
 #else
 #  define OFF 1
 #  define PUP(a) *++(a)
 #endif
 
 /*
    Decode literal, length, and distance codes and write out the resulting
    literal and match bytes until either not enough input or output is
    available, an end-of-block is encountered, or a data error is encountered.
    When large enough input and output buffers are supplied to inflate(), for
    example, a 16K input buffer and a 64K output buffer, more than 95% of the
    inflate execution time is spent in this routine.
 
    Entry assumptions:
 
         state->mode == LEN
         strm->avail_in >= 6
         strm->avail_out >= 258
         start >= strm->avail_out
         state->bits < 8
 
    On return, state->mode is one of:
 
         LEN -- ran out of enough output space or enough available input
         TYPE -- reached end of block code, inflate() to interpret next block
         BAD -- error in block data
 
    Notes:
 
     - The maximum input bits used by a length/distance pair is 15 bits for the
       length code, 5 bits for the length extra, 15 bits for the distance code,
       and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
       Therefore if strm->avail_in >= 6, then there is enough input to avoid
       checking for available input while decoding.
 
     - The maximum bytes that a single length/distance pair can output is 258
       bytes, which is the maximum length that can be coded.  inflate_fast()
       requires strm->avail_out >= 258 for each loop to avoid checking for
       output space.
  */
 void ZLIB_INTERNAL inflate_fast(strm, start)
 z_streamp strm;
 unsigned start;         /* inflate()'s starting value for strm->avail_out */
 {
     struct inflate_state FAR *state;
     z_const unsigned char FAR *in;      /* local strm->next_in */
     z_const unsigned char FAR *last;    /* have enough input while in < last */
     unsigned char FAR *out;     /* local strm->next_out */
     unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
     unsigned char FAR *end;     /* while out < end, enough space available */
 #ifdef INFLATE_STRICT
     unsigned dmax;              /* maximum distance from zlib header */
 #endif
     unsigned wsize;             /* window size or zero if not using window */
     unsigned whave;             /* valid bytes in the window */
     unsigned wnext;             /* window write index */
     unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
     unsigned long hold;         /* local strm->hold */
     unsigned bits;              /* local strm->bits */
     code const FAR *lcode;      /* local strm->lencode */
     code const FAR *dcode;      /* local strm->distcode */
     unsigned lmask;             /* mask for first level of length codes */
     unsigned dmask;             /* mask for first level of distance codes */
     code here;                  /* retrieved table entry */
     unsigned op;                /* code bits, operation, extra bits, or */
                                 /*  window position, window bytes to copy */
     unsigned len;               /* match length, unused bytes */
     unsigned dist;              /* match distance */
     unsigned char FAR *from;    /* where to copy match from */
 
     /* copy state to local variables */
     state = (struct inflate_state FAR *)strm->state;
     in = strm->next_in - OFF;
     last = in + (strm->avail_in - 5);
     out = strm->next_out - OFF;
     beg = out - (start - strm->avail_out);
     end = out + (strm->avail_out - 257);
 #ifdef INFLATE_STRICT
     dmax = state->dmax;
 #endif
     wsize = state->wsize;
     whave = state->whave;
     wnext = state->wnext;
     window = state->window;
     hold = state->hold;
     bits = state->bits;
     lcode = state->lencode;
     dcode = state->distcode;
     lmask = (1U << state->lenbits) - 1;
     dmask = (1U << state->distbits) - 1;
 
     /* decode literals and length/distances until end-of-block or not enough
        input data or output space */
     do {
         if (bits < 15) {
             hold += (unsigned long)(PUP(in)) << bits;
             bits += 8;
             hold += (unsigned long)(PUP(in)) << bits;
             bits += 8;
         }
         here = lcode[hold & lmask];
       dolen:
         op = (unsigned)(here.bits);
         hold >>= op;
         bits -= op;
         op = (unsigned)(here.op);
         if (op == 0) {                          /* literal */
             Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
                     "inflate:         literal '%c'\n" :
                     "inflate:         literal 0x%02x\n", here.val));
             PUP(out) = (unsigned char)(here.val);
         }
         else if (op & 16) {                     /* length base */
             len = (unsigned)(here.val);
             op &= 15;                           /* number of extra bits */
             if (op) {
                 if (bits < op) {
                     hold += (unsigned long)(PUP(in)) << bits;
                     bits += 8;
                 }
                 len += (unsigned)hold & ((1U << op) - 1);
                 hold >>= op;
                 bits -= op;
             }
             Tracevv((stderr, "inflate:         length %u\n", len));
             if (bits < 15) {
                 hold += (unsigned long)(PUP(in)) << bits;
                 bits += 8;
                 hold += (unsigned long)(PUP(in)) << bits;
                 bits += 8;
             }
             here = dcode[hold & dmask];
           dodist:
             op = (unsigned)(here.bits);
             hold >>= op;
             bits -= op;
             op = (unsigned)(here.op);
             if (op & 16) {                      /* distance base */
                 dist = (unsigned)(here.val);
                 op &= 15;                       /* number of extra bits */
                 if (bits < op) {
                     hold += (unsigned long)(PUP(in)) << bits;
                     bits += 8;
                     if (bits < op) {
                         hold += (unsigned long)(PUP(in)) << bits;
                         bits += 8;
                     }
                 }
                 dist += (unsigned)hold & ((1U << op) - 1);
 #ifdef INFLATE_STRICT
                 if (dist > dmax) {
                     strm->msg = (char *)"invalid distance too far back";
                     state->mode = BAD;
                     break;
                 }
 #endif
                 hold >>= op;
                 bits -= op;
                 Tracevv((stderr, "inflate:         distance %u\n", dist));
                 op = (unsigned)(out - beg);     /* max distance in output */
                 if (dist > op) {                /* see if copy from window */
                     op = dist - op;             /* distance back in window */
                     if (op > whave) {
                         if (state->sane) {
                             strm->msg =
                                 (char *)"invalid distance too far back";
                             state->mode = BAD;
                             break;
                         }
 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
                         if (len <= op - whave) {
                             do {
                                 PUP(out) = 0;
                             } while (--len);
                             continue;
                         }
                         len -= op - whave;
                         do {
                             PUP(out) = 0;
                         } while (--op > whave);
                         if (op == 0) {
                             from = out - dist;
                             do {
                                 PUP(out) = PUP(from);
                             } while (--len);
                             continue;
                         }
 #endif
                     }
                     from = window - OFF;
                     if (wnext == 0) {           /* very common case */
                         from += wsize - op;
                         if (op < len) {         /* some from window */
                             len -= op;
                             do {
                                 PUP(out) = PUP(from);
                             } while (--op);
                             from = out - dist;  /* rest from output */
                         }
                     }
                     else if (wnext < op) {      /* wrap around window */
                         from += wsize + wnext - op;
                         op -= wnext;
                         if (op < len) {         /* some from end of window */
                             len -= op;
                             do {
                                 PUP(out) = PUP(from);
                             } while (--op);
                             from = window - OFF;
                             if (wnext < len) {  /* some from start of window */
                                 op = wnext;
                                 len -= op;
                                 do {
                                     PUP(out) = PUP(from);
                                 } while (--op);
                                 from = out - dist;      /* rest from output */
                             }
                         }
                     }
                     else {                      /* contiguous in window */
                         from += wnext - op;
                         if (op < len) {         /* some from window */
                             len -= op;
                             do {
                                 PUP(out) = PUP(from);
                             } while (--op);
                             from = out - dist;  /* rest from output */
                         }
                     }
                     while (len > 2) {
                         PUP(out) = PUP(from);
                         PUP(out) = PUP(from);
                         PUP(out) = PUP(from);
                         len -= 3;
                     }
                     if (len) {
                         PUP(out) = PUP(from);
                         if (len > 1)
                             PUP(out) = PUP(from);
                     }
                 }
                 else {
                     from = out - dist;          /* copy direct from output */
                     do {                        /* minimum length is three */
                         PUP(out) = PUP(from);
                         PUP(out) = PUP(from);
                         PUP(out) = PUP(from);
                         len -= 3;
                     } while (len > 2);
                     if (len) {
                         PUP(out) = PUP(from);
                         if (len > 1)
                             PUP(out) = PUP(from);
                     }
                 }
             }
             else if ((op & 64) == 0) {          /* 2nd level distance code */
                 here = dcode[here.val + (hold & ((1U << op) - 1))];
                 goto dodist;
             }
             else {
                 strm->msg = (char *)"invalid distance code";
                 state->mode = BAD;
                 break;
             }
         }
         else if ((op & 64) == 0) {              /* 2nd level length code */
             here = lcode[here.val + (hold & ((1U << op) - 1))];
             goto dolen;
         }
         else if (op & 32) {                     /* end-of-block */
             Tracevv((stderr, "inflate:         end of block\n"));
             state->mode = TYPE;
             break;
         }
         else {
             strm->msg = (char *)"invalid literal/length code";
             state->mode = BAD;
             break;
         }
     } while (in < last && out < end);
 
     /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
     len = bits >> 3;
     in -= len;
     bits -= len << 3;
     hold &= (1U << bits) - 1;
 
     /* update state and return */
     strm->next_in = in + OFF;
     strm->next_out = out + OFF;
     strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
     strm->avail_out = (unsigned)(out < end ?
                                  257 + (end - out) : 257 - (out - end));
     state->hold = hold;
     state->bits = bits;
     return;
 }
 
 /*
    inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
    - Using bit fields for code structure
    - Different op definition to avoid & for extra bits (do & for table bits)
    - Three separate decoding do-loops for direct, window, and wnext == 0
    - Special case for distance > 1 copies to do overlapped load and store copy
    - Explicit branch predictions (based on measured branch probabilities)
    - Deferring match copy and interspersed it with decoding subsequent codes
    - Swapping literal/length else
    - Swapping window/direct else
    - Larger unrolled copy loops (three is about right)
    - Moving len -= 3 statement into middle of loop
  */
 
 #endif /* !ASMINF */