Chris@4: /* inffast.c -- fast decoding Chris@4: * Copyright (C) 1995-2008, 2010 Mark Adler Chris@4: * For conditions of distribution and use, see copyright notice in zlib.h Chris@4: */ Chris@4: Chris@4: #include "zutil.h" Chris@4: #include "inftrees.h" Chris@4: #include "inflate.h" Chris@4: #include "inffast.h" Chris@4: Chris@4: #ifndef ASMINF Chris@4: Chris@4: /* Allow machine dependent optimization for post-increment or pre-increment. Chris@4: Based on testing to date, Chris@4: Pre-increment preferred for: Chris@4: - PowerPC G3 (Adler) Chris@4: - MIPS R5000 (Randers-Pehrson) Chris@4: Post-increment preferred for: Chris@4: - none Chris@4: No measurable difference: Chris@4: - Pentium III (Anderson) Chris@4: - M68060 (Nikl) Chris@4: */ Chris@4: #ifdef POSTINC Chris@4: # define OFF 0 Chris@4: # define PUP(a) *(a)++ Chris@4: #else Chris@4: # define OFF 1 Chris@4: # define PUP(a) *++(a) Chris@4: #endif Chris@4: Chris@4: /* Chris@4: Decode literal, length, and distance codes and write out the resulting Chris@4: literal and match bytes until either not enough input or output is Chris@4: available, an end-of-block is encountered, or a data error is encountered. Chris@4: When large enough input and output buffers are supplied to inflate(), for Chris@4: example, a 16K input buffer and a 64K output buffer, more than 95% of the Chris@4: inflate execution time is spent in this routine. Chris@4: Chris@4: Entry assumptions: Chris@4: Chris@4: state->mode == LEN Chris@4: strm->avail_in >= 6 Chris@4: strm->avail_out >= 258 Chris@4: start >= strm->avail_out Chris@4: state->bits < 8 Chris@4: Chris@4: On return, state->mode is one of: Chris@4: Chris@4: LEN -- ran out of enough output space or enough available input Chris@4: TYPE -- reached end of block code, inflate() to interpret next block Chris@4: BAD -- error in block data Chris@4: Chris@4: Notes: Chris@4: Chris@4: - The maximum input bits used by a length/distance pair is 15 bits for the Chris@4: length code, 5 bits for the length extra, 15 bits for the distance code, Chris@4: and 13 bits for the distance extra. This totals 48 bits, or six bytes. Chris@4: Therefore if strm->avail_in >= 6, then there is enough input to avoid Chris@4: checking for available input while decoding. Chris@4: Chris@4: - The maximum bytes that a single length/distance pair can output is 258 Chris@4: bytes, which is the maximum length that can be coded. inflate_fast() Chris@4: requires strm->avail_out >= 258 for each loop to avoid checking for Chris@4: output space. Chris@4: */ Chris@4: void ZLIB_INTERNAL inflate_fast(strm, start) Chris@4: z_streamp strm; Chris@4: unsigned start; /* inflate()'s starting value for strm->avail_out */ Chris@4: { Chris@4: struct inflate_state FAR *state; Chris@4: unsigned char FAR *in; /* local strm->next_in */ Chris@4: unsigned char FAR *last; /* while in < last, enough input available */ Chris@4: unsigned char FAR *out; /* local strm->next_out */ Chris@4: unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ Chris@4: unsigned char FAR *end; /* while out < end, enough space available */ Chris@4: #ifdef INFLATE_STRICT Chris@4: unsigned dmax; /* maximum distance from zlib header */ Chris@4: #endif Chris@4: unsigned wsize; /* window size or zero if not using window */ Chris@4: unsigned whave; /* valid bytes in the window */ Chris@4: unsigned wnext; /* window write index */ Chris@4: unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ Chris@4: unsigned long hold; /* local strm->hold */ Chris@4: unsigned bits; /* local strm->bits */ Chris@4: code const FAR *lcode; /* local strm->lencode */ Chris@4: code const FAR *dcode; /* local strm->distcode */ Chris@4: unsigned lmask; /* mask for first level of length codes */ Chris@4: unsigned dmask; /* mask for first level of distance codes */ Chris@4: code here; /* retrieved table entry */ Chris@4: unsigned op; /* code bits, operation, extra bits, or */ Chris@4: /* window position, window bytes to copy */ Chris@4: unsigned len; /* match length, unused bytes */ Chris@4: unsigned dist; /* match distance */ Chris@4: unsigned char FAR *from; /* where to copy match from */ Chris@4: Chris@4: /* copy state to local variables */ Chris@4: state = (struct inflate_state FAR *)strm->state; Chris@4: in = strm->next_in - OFF; Chris@4: last = in + (strm->avail_in - 5); Chris@4: out = strm->next_out - OFF; Chris@4: beg = out - (start - strm->avail_out); Chris@4: end = out + (strm->avail_out - 257); Chris@4: #ifdef INFLATE_STRICT Chris@4: dmax = state->dmax; Chris@4: #endif Chris@4: wsize = state->wsize; Chris@4: whave = state->whave; Chris@4: wnext = state->wnext; Chris@4: window = state->window; Chris@4: hold = state->hold; Chris@4: bits = state->bits; Chris@4: lcode = state->lencode; Chris@4: dcode = state->distcode; Chris@4: lmask = (1U << state->lenbits) - 1; Chris@4: dmask = (1U << state->distbits) - 1; Chris@4: Chris@4: /* decode literals and length/distances until end-of-block or not enough Chris@4: input data or output space */ Chris@4: do { Chris@4: if (bits < 15) { Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: } Chris@4: here = lcode[hold & lmask]; Chris@4: dolen: Chris@4: op = (unsigned)(here.bits); Chris@4: hold >>= op; Chris@4: bits -= op; Chris@4: op = (unsigned)(here.op); Chris@4: if (op == 0) { /* literal */ Chris@4: Tracevv((stderr, here.val >= 0x20 && here.val < 0x7f ? Chris@4: "inflate: literal '%c'\n" : Chris@4: "inflate: literal 0x%02x\n", here.val)); Chris@4: PUP(out) = (unsigned char)(here.val); Chris@4: } Chris@4: else if (op & 16) { /* length base */ Chris@4: len = (unsigned)(here.val); Chris@4: op &= 15; /* number of extra bits */ Chris@4: if (op) { Chris@4: if (bits < op) { Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: } Chris@4: len += (unsigned)hold & ((1U << op) - 1); Chris@4: hold >>= op; Chris@4: bits -= op; Chris@4: } Chris@4: Tracevv((stderr, "inflate: length %u\n", len)); Chris@4: if (bits < 15) { Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: } Chris@4: here = dcode[hold & dmask]; Chris@4: dodist: Chris@4: op = (unsigned)(here.bits); Chris@4: hold >>= op; Chris@4: bits -= op; Chris@4: op = (unsigned)(here.op); Chris@4: if (op & 16) { /* distance base */ Chris@4: dist = (unsigned)(here.val); Chris@4: op &= 15; /* number of extra bits */ Chris@4: if (bits < op) { Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: if (bits < op) { Chris@4: hold += (unsigned long)(PUP(in)) << bits; Chris@4: bits += 8; Chris@4: } Chris@4: } Chris@4: dist += (unsigned)hold & ((1U << op) - 1); Chris@4: #ifdef INFLATE_STRICT Chris@4: if (dist > dmax) { Chris@4: strm->msg = (char *)"invalid distance too far back"; Chris@4: state->mode = BAD; Chris@4: break; Chris@4: } Chris@4: #endif Chris@4: hold >>= op; Chris@4: bits -= op; Chris@4: Tracevv((stderr, "inflate: distance %u\n", dist)); Chris@4: op = (unsigned)(out - beg); /* max distance in output */ Chris@4: if (dist > op) { /* see if copy from window */ Chris@4: op = dist - op; /* distance back in window */ Chris@4: if (op > whave) { Chris@4: if (state->sane) { Chris@4: strm->msg = Chris@4: (char *)"invalid distance too far back"; Chris@4: state->mode = BAD; Chris@4: break; Chris@4: } Chris@4: #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR Chris@4: if (len <= op - whave) { Chris@4: do { Chris@4: PUP(out) = 0; Chris@4: } while (--len); Chris@4: continue; Chris@4: } Chris@4: len -= op - whave; Chris@4: do { Chris@4: PUP(out) = 0; Chris@4: } while (--op > whave); Chris@4: if (op == 0) { Chris@4: from = out - dist; Chris@4: do { Chris@4: PUP(out) = PUP(from); Chris@4: } while (--len); Chris@4: continue; Chris@4: } Chris@4: #endif Chris@4: } Chris@4: from = window - OFF; Chris@4: if (wnext == 0) { /* very common case */ Chris@4: from += wsize - op; Chris@4: if (op < len) { /* some from window */ Chris@4: len -= op; Chris@4: do { Chris@4: PUP(out) = PUP(from); Chris@4: } while (--op); Chris@4: from = out - dist; /* rest from output */ Chris@4: } Chris@4: } Chris@4: else if (wnext < op) { /* wrap around window */ Chris@4: from += wsize + wnext - op; Chris@4: op -= wnext; Chris@4: if (op < len) { /* some from end of window */ Chris@4: len -= op; Chris@4: do { Chris@4: PUP(out) = PUP(from); Chris@4: } while (--op); Chris@4: from = window - OFF; Chris@4: if (wnext < len) { /* some from start of window */ Chris@4: op = wnext; Chris@4: len -= op; Chris@4: do { Chris@4: PUP(out) = PUP(from); Chris@4: } while (--op); Chris@4: from = out - dist; /* rest from output */ Chris@4: } Chris@4: } Chris@4: } Chris@4: else { /* contiguous in window */ Chris@4: from += wnext - op; Chris@4: if (op < len) { /* some from window */ Chris@4: len -= op; Chris@4: do { Chris@4: PUP(out) = PUP(from); Chris@4: } while (--op); Chris@4: from = out - dist; /* rest from output */ Chris@4: } Chris@4: } Chris@4: while (len > 2) { Chris@4: PUP(out) = PUP(from); Chris@4: PUP(out) = PUP(from); Chris@4: PUP(out) = PUP(from); Chris@4: len -= 3; Chris@4: } Chris@4: if (len) { Chris@4: PUP(out) = PUP(from); Chris@4: if (len > 1) Chris@4: PUP(out) = PUP(from); Chris@4: } Chris@4: } Chris@4: else { Chris@4: from = out - dist; /* copy direct from output */ Chris@4: do { /* minimum length is three */ Chris@4: PUP(out) = PUP(from); Chris@4: PUP(out) = PUP(from); Chris@4: PUP(out) = PUP(from); Chris@4: len -= 3; Chris@4: } while (len > 2); Chris@4: if (len) { Chris@4: PUP(out) = PUP(from); Chris@4: if (len > 1) Chris@4: PUP(out) = PUP(from); Chris@4: } Chris@4: } Chris@4: } Chris@4: else if ((op & 64) == 0) { /* 2nd level distance code */ Chris@4: here = dcode[here.val + (hold & ((1U << op) - 1))]; Chris@4: goto dodist; Chris@4: } Chris@4: else { Chris@4: strm->msg = (char *)"invalid distance code"; Chris@4: state->mode = BAD; Chris@4: break; Chris@4: } Chris@4: } Chris@4: else if ((op & 64) == 0) { /* 2nd level length code */ Chris@4: here = lcode[here.val + (hold & ((1U << op) - 1))]; Chris@4: goto dolen; Chris@4: } Chris@4: else if (op & 32) { /* end-of-block */ Chris@4: Tracevv((stderr, "inflate: end of block\n")); Chris@4: state->mode = TYPE; Chris@4: break; Chris@4: } Chris@4: else { Chris@4: strm->msg = (char *)"invalid literal/length code"; Chris@4: state->mode = BAD; Chris@4: break; Chris@4: } Chris@4: } while (in < last && out < end); Chris@4: Chris@4: /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ Chris@4: len = bits >> 3; Chris@4: in -= len; Chris@4: bits -= len << 3; Chris@4: hold &= (1U << bits) - 1; Chris@4: Chris@4: /* update state and return */ Chris@4: strm->next_in = in + OFF; Chris@4: strm->next_out = out + OFF; Chris@4: strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); Chris@4: strm->avail_out = (unsigned)(out < end ? Chris@4: 257 + (end - out) : 257 - (out - end)); Chris@4: state->hold = hold; Chris@4: state->bits = bits; Chris@4: return; Chris@4: } Chris@4: Chris@4: /* Chris@4: inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): Chris@4: - Using bit fields for code structure Chris@4: - Different op definition to avoid & for extra bits (do & for table bits) Chris@4: - Three separate decoding do-loops for direct, window, and wnext == 0 Chris@4: - Special case for distance > 1 copies to do overlapped load and store copy Chris@4: - Explicit branch predictions (based on measured branch probabilities) Chris@4: - Deferring match copy and interspersed it with decoding subsequent codes Chris@4: - Swapping literal/length else Chris@4: - Swapping window/direct else Chris@4: - Larger unrolled copy loops (three is about right) Chris@4: - Moving len -= 3 statement into middle of loop Chris@4: */ Chris@4: Chris@4: #endif /* !ASMINF */