[331] | 1 | /* inffast.c -- fast decoding
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| 2 | * Copyright (C) 1995-2017 Mark Adler
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| 3 | * For conditions of distribution and use, see copyright notice in zlib.h
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| 4 | */
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| 5 |
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| 6 | #include "zutil.h"
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| 7 | #include "inftrees.h"
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| 8 | #include "inflate.h"
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| 9 | #include "inffast.h"
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| 10 |
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| 11 | #ifdef ASMINF
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| 12 | # pragma message("Assembler code may have bugs -- use at your own risk")
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| 13 | #else
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| 14 |
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| 15 | /*
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| 16 | Decode literal, length, and distance codes and write out the resulting
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| 17 | literal and match bytes until either not enough input or output is
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| 18 | available, an end-of-block is encountered, or a data error is encountered.
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| 19 | When large enough input and output buffers are supplied to inflate(), for
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| 20 | example, a 16K input buffer and a 64K output buffer, more than 95% of the
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| 21 | inflate execution time is spent in this routine.
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| 22 |
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| 23 | Entry assumptions:
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| 24 |
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| 25 | state->mode == LEN
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| 26 | strm->avail_in >= 6
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| 27 | strm->avail_out >= 258
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| 28 | start >= strm->avail_out
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| 29 | state->bits < 8
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| 30 |
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| 31 | On return, state->mode is one of:
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| 32 |
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| 33 | LEN -- ran out of enough output space or enough available input
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| 34 | TYPE -- reached end of block code, inflate() to interpret next block
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| 35 | BAD -- error in block data
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| 36 |
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| 37 | Notes:
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| 38 |
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| 39 | - The maximum input bits used by a length/distance pair is 15 bits for the
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| 40 | length code, 5 bits for the length extra, 15 bits for the distance code,
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| 41 | and 13 bits for the distance extra. This totals 48 bits, or six bytes.
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| 42 | Therefore if strm->avail_in >= 6, then there is enough input to avoid
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| 43 | checking for available input while decoding.
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| 44 |
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| 45 | - The maximum bytes that a single length/distance pair can output is 258
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| 46 | bytes, which is the maximum length that can be coded. inflate_fast()
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| 47 | requires strm->avail_out >= 258 for each loop to avoid checking for
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| 48 | output space.
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| 49 | */
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| 50 | void ZLIB_INTERNAL inflate_fast(strm, start)
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| 51 | z_streamp strm;
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| 52 | unsigned start; /* inflate()'s starting value for strm->avail_out */
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| 53 | {
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| 54 | struct inflate_state FAR *state;
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| 55 | z_const unsigned char FAR *in; /* local strm->next_in */
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| 56 | z_const unsigned char FAR *last; /* have enough input while in < last */
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| 57 | unsigned char FAR *out; /* local strm->next_out */
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| 58 | unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
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| 59 | unsigned char FAR *end; /* while out < end, enough space available */
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| 60 | #ifdef INFLATE_STRICT
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| 61 | unsigned dmax; /* maximum distance from zlib header */
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| 62 | #endif
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| 63 | unsigned wsize; /* window size or zero if not using window */
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| 64 | unsigned whave; /* valid bytes in the window */
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| 65 | unsigned wnext; /* window write index */
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| 66 | unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */
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| 67 | unsigned long hold; /* local strm->hold */
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| 68 | unsigned bits; /* local strm->bits */
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| 69 | code const FAR *lcode; /* local strm->lencode */
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| 70 | code const FAR *dcode; /* local strm->distcode */
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| 71 | unsigned lmask; /* mask for first level of length codes */
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| 72 | unsigned dmask; /* mask for first level of distance codes */
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| 73 | code here; /* retrieved table entry */
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| 74 | unsigned op; /* code bits, operation, extra bits, or */
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| 75 | /* window position, window bytes to copy */
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| 76 | unsigned len; /* match length, unused bytes */
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| 77 | unsigned dist; /* match distance */
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| 78 | unsigned char FAR *from; /* where to copy match from */
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| 79 |
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| 80 | /* copy state to local variables */
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| 81 | state = (struct inflate_state FAR *)strm->state;
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| 82 | in = strm->next_in;
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| 83 | last = in + (strm->avail_in - 5);
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| 84 | out = strm->next_out;
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| 85 | beg = out - (start - strm->avail_out);
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| 86 | end = out + (strm->avail_out - 257);
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| 87 | #ifdef INFLATE_STRICT
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| 88 | dmax = state->dmax;
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| 89 | #endif
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| 90 | wsize = state->wsize;
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| 91 | whave = state->whave;
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| 92 | wnext = state->wnext;
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| 93 | window = state->window;
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| 94 | hold = state->hold;
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| 95 | bits = state->bits;
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| 96 | lcode = state->lencode;
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| 97 | dcode = state->distcode;
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| 98 | lmask = (1U << state->lenbits) - 1;
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| 99 | dmask = (1U << state->distbits) - 1;
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| 100 |
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| 101 | /* decode literals and length/distances until end-of-block or not enough
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| 102 | input data or output space */
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| 103 | do {
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| 104 | if (bits < 15) {
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| 105 | hold += (unsigned long)(*in++) << bits;
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| 106 | bits += 8;
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| 107 | hold += (unsigned long)(*in++) << bits;
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| 108 | bits += 8;
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| 109 | }
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| 110 | here = lcode[hold & lmask];
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| 111 | dolen:
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| 112 | op = (unsigned)(here.bits);
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| 113 | hold >>= op;
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| 114 | bits -= op;
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| 115 | op = (unsigned)(here.op);
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| 116 | if (op == 0) { /* literal */
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| 117 | Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ?
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| 118 | "inflate: literal '%c'\n" :
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| 119 | "inflate: literal 0x%02x\n", here.val));
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| 120 | *out++ = (unsigned char)(here.val);
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| 121 | }
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| 122 | else if (op & 16) { /* length base */
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| 123 | len = (unsigned)(here.val);
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| 124 | op &= 15; /* number of extra bits */
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| 125 | if (op) {
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| 126 | if (bits < op) {
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| 127 | hold += (unsigned long)(*in++) << bits;
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| 128 | bits += 8;
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| 129 | }
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| 130 | len += (unsigned)hold & ((1U << op) - 1);
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| 131 | hold >>= op;
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| 132 | bits -= op;
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| 133 | }
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| 134 | Tracevv((stderr, "inflate: length %u\n", len));
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| 135 | if (bits < 15) {
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| 136 | hold += (unsigned long)(*in++) << bits;
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| 137 | bits += 8;
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| 138 | hold += (unsigned long)(*in++) << bits;
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| 139 | bits += 8;
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| 140 | }
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| 141 | here = dcode[hold & dmask];
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| 142 | dodist:
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| 143 | op = (unsigned)(here.bits);
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| 144 | hold >>= op;
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| 145 | bits -= op;
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| 146 | op = (unsigned)(here.op);
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| 147 | if (op & 16) { /* distance base */
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| 148 | dist = (unsigned)(here.val);
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| 149 | op &= 15; /* number of extra bits */
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| 150 | if (bits < op) {
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| 151 | hold += (unsigned long)(*in++) << bits;
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| 152 | bits += 8;
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| 153 | if (bits < op) {
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| 154 | hold += (unsigned long)(*in++) << bits;
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| 155 | bits += 8;
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| 156 | }
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| 157 | }
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| 158 | dist += (unsigned)hold & ((1U << op) - 1);
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| 159 | #ifdef INFLATE_STRICT
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| 160 | if (dist > dmax) {
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| 161 | strm->msg = (char *)"invalid distance too far back";
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| 162 | state->mode = BAD;
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| 163 | break;
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| 164 | }
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| 165 | #endif
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| 166 | hold >>= op;
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| 167 | bits -= op;
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| 168 | Tracevv((stderr, "inflate: distance %u\n", dist));
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| 169 | op = (unsigned)(out - beg); /* max distance in output */
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| 170 | if (dist > op) { /* see if copy from window */
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| 171 | op = dist - op; /* distance back in window */
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| 172 | if (op > whave) {
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| 173 | if (state->sane) {
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| 174 | strm->msg =
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| 175 | (char *)"invalid distance too far back";
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| 176 | state->mode = BAD;
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| 177 | break;
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| 178 | }
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| 179 | #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
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| 180 | if (len <= op - whave) {
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| 181 | do {
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| 182 | *out++ = 0;
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| 183 | } while (--len);
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| 184 | continue;
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| 185 | }
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| 186 | len -= op - whave;
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| 187 | do {
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| 188 | *out++ = 0;
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| 189 | } while (--op > whave);
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| 190 | if (op == 0) {
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| 191 | from = out - dist;
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| 192 | do {
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| 193 | *out++ = *from++;
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| 194 | } while (--len);
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| 195 | continue;
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| 196 | }
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| 197 | #endif
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| 198 | }
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| 199 | from = window;
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| 200 | if (wnext == 0) { /* very common case */
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| 201 | from += wsize - op;
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| 202 | if (op < len) { /* some from window */
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| 203 | len -= op;
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| 204 | do {
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| 205 | *out++ = *from++;
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| 206 | } while (--op);
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| 207 | from = out - dist; /* rest from output */
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| 208 | }
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| 209 | }
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| 210 | else if (wnext < op) { /* wrap around window */
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| 211 | from += wsize + wnext - op;
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| 212 | op -= wnext;
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| 213 | if (op < len) { /* some from end of window */
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| 214 | len -= op;
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| 215 | do {
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| 216 | *out++ = *from++;
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| 217 | } while (--op);
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| 218 | from = window;
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| 219 | if (wnext < len) { /* some from start of window */
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| 220 | op = wnext;
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| 221 | len -= op;
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| 222 | do {
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| 223 | *out++ = *from++;
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| 224 | } while (--op);
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| 225 | from = out - dist; /* rest from output */
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| 226 | }
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| 227 | }
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| 228 | }
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| 229 | else { /* contiguous in window */
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| 230 | from += wnext - op;
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| 231 | if (op < len) { /* some from window */
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| 232 | len -= op;
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| 233 | do {
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| 234 | *out++ = *from++;
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| 235 | } while (--op);
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| 236 | from = out - dist; /* rest from output */
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| 237 | }
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| 238 | }
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| 239 | while (len > 2) {
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| 240 | *out++ = *from++;
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| 241 | *out++ = *from++;
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| 242 | *out++ = *from++;
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| 243 | len -= 3;
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| 244 | }
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| 245 | if (len) {
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| 246 | *out++ = *from++;
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| 247 | if (len > 1)
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| 248 | *out++ = *from++;
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| 249 | }
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| 250 | }
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| 251 | else {
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| 252 | from = out - dist; /* copy direct from output */
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| 253 | do { /* minimum length is three */
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| 254 | *out++ = *from++;
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| 255 | *out++ = *from++;
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| 256 | *out++ = *from++;
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| 257 | len -= 3;
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| 258 | } while (len > 2);
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| 259 | if (len) {
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| 260 | *out++ = *from++;
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| 261 | if (len > 1)
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| 262 | *out++ = *from++;
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| 263 | }
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| 264 | }
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| 265 | }
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| 266 | else if ((op & 64) == 0) { /* 2nd level distance code */
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| 267 | here = dcode[here.val + (hold & ((1U << op) - 1))];
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| 268 | goto dodist;
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| 269 | }
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| 270 | else {
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| 271 | strm->msg = (char *)"invalid distance code";
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| 272 | state->mode = BAD;
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| 273 | break;
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| 274 | }
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| 275 | }
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| 276 | else if ((op & 64) == 0) { /* 2nd level length code */
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| 277 | here = lcode[here.val + (hold & ((1U << op) - 1))];
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| 278 | goto dolen;
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| 279 | }
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| 280 | else if (op & 32) { /* end-of-block */
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| 281 | Tracevv((stderr, "inflate: end of block\n"));
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| 282 | state->mode = TYPE;
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| 283 | break;
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| 284 | }
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| 285 | else {
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| 286 | strm->msg = (char *)"invalid literal/length code";
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| 287 | state->mode = BAD;
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| 288 | break;
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| 289 | }
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| 290 | } while (in < last && out < end);
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| 291 |
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| 292 | /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
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| 293 | len = bits >> 3;
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| 294 | in -= len;
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| 295 | bits -= len << 3;
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| 296 | hold &= (1U << bits) - 1;
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| 297 |
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| 298 | /* update state and return */
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| 299 | strm->next_in = in;
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| 300 | strm->next_out = out;
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| 301 | strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
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| 302 | strm->avail_out = (unsigned)(out < end ?
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| 303 | 257 + (end - out) : 257 - (out - end));
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| 304 | state->hold = hold;
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| 305 | state->bits = bits;
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| 306 | return;
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| 307 | }
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| 308 |
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| 309 | /*
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| 310 | inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
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| 311 | - Using bit fields for code structure
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| 312 | - Different op definition to avoid & for extra bits (do & for table bits)
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| 313 | - Three separate decoding do-loops for direct, window, and wnext == 0
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| 314 | - Special case for distance > 1 copies to do overlapped load and store copy
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| 315 | - Explicit branch predictions (based on measured branch probabilities)
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| 316 | - Deferring match copy and interspersed it with decoding subsequent codes
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| 317 | - Swapping literal/length else
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| 318 | - Swapping window/direct else
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| 319 | - Larger unrolled copy loops (three is about right)
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| 320 | - Moving len -= 3 statement into middle of loop
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| 321 | */
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| 322 |
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| 323 | #endif /* !ASMINF */
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