| /* inffast.c -- fast decoding |
| * Copyright (C) 1995-2017 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" |
| |
| #ifdef ASMINF |
| # pragma message("Assembler code may have bugs -- use at your own risk") |
| #else |
| |
| /* |
| 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 >= INFLATE_FAST_MIN_INPUT (6 bytes) |
| strm->avail_out >= INFLATE_FAST_MIN_OUTPUT (258 bytes) |
| 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: |
| |
| INFLATE_FAST_MIN_INPUT: 6 bytes |
| |
| - 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. |
| |
| INFLATE_FAST_MIN_OUTPUT: 258 bytes |
| |
| - 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 |
| available output space while decoding. |
| */ |
| 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; |
| last = in + (strm->avail_in - (INFLATE_FAST_MIN_INPUT - 1)); |
| out = strm->next_out; |
| beg = out - (start - strm->avail_out); |
| end = out + (strm->avail_out - (INFLATE_FAST_MIN_OUTPUT - 1)); |
| #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)(*in++) << bits; |
| bits += 8; |
| hold += (unsigned long)(*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)); |
| *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)(*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)(*in++) << bits; |
| bits += 8; |
| hold += (unsigned long)(*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)(*in++) << bits; |
| bits += 8; |
| if (bits < op) { |
| hold += (unsigned long)(*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 { |
| *out++ = 0; |
| } while (--len); |
| continue; |
| } |
| len -= op - whave; |
| do { |
| *out++ = 0; |
| } while (--op > whave); |
| if (op == 0) { |
| from = out - dist; |
| do { |
| *out++ = *from++; |
| } while (--len); |
| continue; |
| } |
| #endif |
| } |
| from = window; |
| if (wnext == 0) { /* very common case */ |
| from += wsize - op; |
| if (op < len) { /* some from window */ |
| len -= op; |
| do { |
| *out++ = *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 { |
| *out++ = *from++; |
| } while (--op); |
| from = window; |
| if (wnext < len) { /* some from start of window */ |
| op = wnext; |
| len -= op; |
| do { |
| *out++ = *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 { |
| *out++ = *from++; |
| } while (--op); |
| from = out - dist; /* rest from output */ |
| } |
| } |
| while (len > 2) { |
| *out++ = *from++; |
| *out++ = *from++; |
| *out++ = *from++; |
| len -= 3; |
| } |
| if (len) { |
| *out++ = *from++; |
| if (len > 1) |
| *out++ = *from++; |
| } |
| } |
| else { |
| from = out - dist; /* copy direct from output */ |
| do { /* minimum length is three */ |
| *out++ = *from++; |
| *out++ = *from++; |
| *out++ = *from++; |
| len -= 3; |
| } while (len > 2); |
| if (len) { |
| *out++ = *from++; |
| if (len > 1) |
| *out++ = *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; |
| strm->next_out = out; |
| strm->avail_in = (unsigned)(in < last ? |
| (INFLATE_FAST_MIN_INPUT - 1) + (last - in) : |
| (INFLATE_FAST_MIN_INPUT - 1) - (in - last)); |
| strm->avail_out = (unsigned)(out < end ? |
| (INFLATE_FAST_MIN_OUTPUT - 1) + (end - out) : |
| (INFLATE_FAST_MIN_OUTPUT - 1) - (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 */ |
