/* inffast.c -- fast decoding * Copyright (C) 1995-2003 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) - 68060 (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 inflate_fast(strm, start) z_streamp strm; unsigned start; /* inflate()'s starting value for strm->avail_out */ { struct inflate_state FAR *state; unsigned char FAR *in; /* local strm->next_in */ unsigned char FAR *last; /* while in < last, enough input available */ 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 */ unsigned wsize; /* window size or zero if not using window */ unsigned whave; /* valid bytes in the window */ unsigned write; /* 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 this; /* 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); wsize = state->wsize; whave = state->whave; write = state->write; 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; } this = lcode[hold & lmask]; dolen: op = (unsigned)(this.bits); hold >>= op; bits -= op; op = (unsigned)(this.op); if (op == 0) { /* literal */ Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? "inflate: literal '%c'\n" : "inflate: literal 0x%02x\n", this.val)); PUP(out) = (unsigned char)(this.val); } else if (op & 16) { /* length base */ len = (unsigned)(this.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; } this = dcode[hold & dmask]; dodist: op = (unsigned)(this.bits); hold >>= op; bits -= op; op = (unsigned)(this.op); if (op & 16) { /* distance base */ dist = (unsigned)(this.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); 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) { strm->msg = (char *)"invalid distance too far back"; state->mode = BAD; break; } from = window - OFF; if (write == 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 (write < op) { /* wrap around window */ from += wsize + write - op; op -= write; if (op < len) { /* some from end of window */ len -= op; do { PUP(out) = PUP(from); } while (--op); from = window - OFF; if (write < len) { /* some from start of window */ op = write; len -= op; do { PUP(out) = PUP(from); } while (--op); from = out - dist; /* rest from output */ } } } else { /* contiguous in window */ from += write - 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 */ this = dcode[this.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 */ this = lcode[this.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 write == 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 */