inffast.c revision 131380
1131380Stjr/* inffast.c -- fast decoding 2131380Stjr * Copyright (C) 1995-2003 Mark Adler 3131380Stjr * For conditions of distribution and use, see copyright notice in zlib.h 417651Speter */ 517651Speter 684228Sdillon#include <sys/cdefs.h> 784228Sdillon__FBSDID("$FreeBSD: head/lib/libz/inffast.c 131380 2004-06-30 23:54:46Z tjr $"); 884228Sdillon 917651Speter#include "zutil.h" 1017651Speter#include "inftrees.h" 11131380Stjr#include "inflate.h" 1217651Speter#include "inffast.h" 1317651Speter 14131380Stjr#ifndef ASMINF 1517651Speter 16131380Stjr/* Allow machine dependent optimization for post-increment or pre-increment. 17131380Stjr Based on testing to date, 18131380Stjr Pre-increment preferred for: 19131380Stjr - PowerPC G3 (Adler) 20131380Stjr - MIPS R5000 (Randers-Pehrson) 21131380Stjr Post-increment preferred for: 22131380Stjr - none 23131380Stjr No measurable difference: 24131380Stjr - Pentium III (Anderson) 25131380Stjr - 68060 (Nikl) 26131380Stjr */ 27131380Stjr#ifdef POSTINC 28131380Stjr# define OFF 0 29131380Stjr# define PUP(a) *(a)++ 30131380Stjr#else 31131380Stjr# define OFF 1 32131380Stjr# define PUP(a) *++(a) 33131380Stjr#endif 3417651Speter 35131380Stjr/* 36131380Stjr Decode literal, length, and distance codes and write out the resulting 37131380Stjr literal and match bytes until either not enough input or output is 38131380Stjr available, an end-of-block is encountered, or a data error is encountered. 39131380Stjr When large enough input and output buffers are supplied to inflate(), for 40131380Stjr example, a 16K input buffer and a 64K output buffer, more than 95% of the 41131380Stjr inflate execution time is spent in this routine. 4217651Speter 43131380Stjr Entry assumptions: 4417651Speter 45131380Stjr state->mode == LEN 46131380Stjr strm->avail_in >= 6 47131380Stjr strm->avail_out >= 258 48131380Stjr start >= strm->avail_out 49131380Stjr state->bits < 8 5017651Speter 51131380Stjr On return, state->mode is one of: 5217651Speter 53131380Stjr LEN -- ran out of enough output space or enough available input 54131380Stjr TYPE -- reached end of block code, inflate() to interpret next block 55131380Stjr BAD -- error in block data 5617651Speter 57131380Stjr Notes: 5817651Speter 59131380Stjr - The maximum input bits used by a length/distance pair is 15 bits for the 60131380Stjr length code, 5 bits for the length extra, 15 bits for the distance code, 61131380Stjr and 13 bits for the distance extra. This totals 48 bits, or six bytes. 62131380Stjr Therefore if strm->avail_in >= 6, then there is enough input to avoid 63131380Stjr checking for available input while decoding. 6417651Speter 65131380Stjr - The maximum bytes that a single length/distance pair can output is 258 66131380Stjr bytes, which is the maximum length that can be coded. inflate_fast() 67131380Stjr requires strm->avail_out >= 258 for each loop to avoid checking for 68131380Stjr output space. 69131380Stjr */ 70131380Stjrvoid inflate_fast(strm, start) 71131380Stjrz_streamp strm; 72131380Stjrunsigned start; /* inflate()'s starting value for strm->avail_out */ 73131380Stjr{ 74131380Stjr struct inflate_state FAR *state; 75131380Stjr unsigned char FAR *in; /* local strm->next_in */ 76131380Stjr unsigned char FAR *last; /* while in < last, enough input available */ 77131380Stjr unsigned char FAR *out; /* local strm->next_out */ 78131380Stjr unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ 79131380Stjr unsigned char FAR *end; /* while out < end, enough space available */ 80131380Stjr unsigned wsize; /* window size or zero if not using window */ 81131380Stjr unsigned whave; /* valid bytes in the window */ 82131380Stjr unsigned write; /* window write index */ 83131380Stjr unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ 84131380Stjr unsigned long hold; /* local strm->hold */ 85131380Stjr unsigned bits; /* local strm->bits */ 86131380Stjr code const FAR *lcode; /* local strm->lencode */ 87131380Stjr code const FAR *dcode; /* local strm->distcode */ 88131380Stjr unsigned lmask; /* mask for first level of length codes */ 89131380Stjr unsigned dmask; /* mask for first level of distance codes */ 90131380Stjr code this; /* retrieved table entry */ 91131380Stjr unsigned op; /* code bits, operation, extra bits, or */ 92131380Stjr /* window position, window bytes to copy */ 93131380Stjr unsigned len; /* match length, unused bytes */ 94131380Stjr unsigned dist; /* match distance */ 95131380Stjr unsigned char FAR *from; /* where to copy match from */ 96131380Stjr 97131380Stjr /* copy state to local variables */ 98131380Stjr state = (struct inflate_state FAR *)strm->state; 99131380Stjr in = strm->next_in - OFF; 100131380Stjr last = in + (strm->avail_in - 5); 101131380Stjr out = strm->next_out - OFF; 102131380Stjr beg = out - (start - strm->avail_out); 103131380Stjr end = out + (strm->avail_out - 257); 104131380Stjr wsize = state->wsize; 105131380Stjr whave = state->whave; 106131380Stjr write = state->write; 107131380Stjr window = state->window; 108131380Stjr hold = state->hold; 109131380Stjr bits = state->bits; 110131380Stjr lcode = state->lencode; 111131380Stjr dcode = state->distcode; 112131380Stjr lmask = (1U << state->lenbits) - 1; 113131380Stjr dmask = (1U << state->distbits) - 1; 114131380Stjr 115131380Stjr /* decode literals and length/distances until end-of-block or not enough 116131380Stjr input data or output space */ 117131380Stjr do { 118131380Stjr if (bits < 15) { 119131380Stjr hold += (unsigned long)(PUP(in)) << bits; 120131380Stjr bits += 8; 121131380Stjr hold += (unsigned long)(PUP(in)) << bits; 122131380Stjr bits += 8; 123131380Stjr } 124131380Stjr this = lcode[hold & lmask]; 125131380Stjr dolen: 126131380Stjr op = (unsigned)(this.bits); 127131380Stjr hold >>= op; 128131380Stjr bits -= op; 129131380Stjr op = (unsigned)(this.op); 130131380Stjr if (op == 0) { /* literal */ 131131380Stjr Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? 132131380Stjr "inflate: literal '%c'\n" : 133131380Stjr "inflate: literal 0x%02x\n", this.val)); 134131380Stjr PUP(out) = (unsigned char)(this.val); 135131380Stjr } 136131380Stjr else if (op & 16) { /* length base */ 137131380Stjr len = (unsigned)(this.val); 138131380Stjr op &= 15; /* number of extra bits */ 139131380Stjr if (op) { 140131380Stjr if (bits < op) { 141131380Stjr hold += (unsigned long)(PUP(in)) << bits; 142131380Stjr bits += 8; 143131380Stjr } 144131380Stjr len += (unsigned)hold & ((1U << op) - 1); 145131380Stjr hold >>= op; 146131380Stjr bits -= op; 14717651Speter } 148131380Stjr Tracevv((stderr, "inflate: length %u\n", len)); 149131380Stjr if (bits < 15) { 150131380Stjr hold += (unsigned long)(PUP(in)) << bits; 151131380Stjr bits += 8; 152131380Stjr hold += (unsigned long)(PUP(in)) << bits; 153131380Stjr bits += 8; 15492114Sgreen } 155131380Stjr this = dcode[hold & dmask]; 156131380Stjr dodist: 157131380Stjr op = (unsigned)(this.bits); 158131380Stjr hold >>= op; 159131380Stjr bits -= op; 160131380Stjr op = (unsigned)(this.op); 161131380Stjr if (op & 16) { /* distance base */ 162131380Stjr dist = (unsigned)(this.val); 163131380Stjr op &= 15; /* number of extra bits */ 164131380Stjr if (bits < op) { 165131380Stjr hold += (unsigned long)(PUP(in)) << bits; 166131380Stjr bits += 8; 167131380Stjr if (bits < op) { 168131380Stjr hold += (unsigned long)(PUP(in)) << bits; 169131380Stjr bits += 8; 170131380Stjr } 171131380Stjr } 172131380Stjr dist += (unsigned)hold & ((1U << op) - 1); 173131380Stjr hold >>= op; 174131380Stjr bits -= op; 175131380Stjr Tracevv((stderr, "inflate: distance %u\n", dist)); 176131380Stjr op = (unsigned)(out - beg); /* max distance in output */ 177131380Stjr if (dist > op) { /* see if copy from window */ 178131380Stjr op = dist - op; /* distance back in window */ 179131380Stjr if (op > whave) { 180131380Stjr strm->msg = (char *)"invalid distance too far back"; 181131380Stjr state->mode = BAD; 182131380Stjr break; 183131380Stjr } 184131380Stjr from = window - OFF; 185131380Stjr if (write == 0) { /* very common case */ 186131380Stjr from += wsize - op; 187131380Stjr if (op < len) { /* some from window */ 188131380Stjr len -= op; 189131380Stjr do { 190131380Stjr PUP(out) = PUP(from); 191131380Stjr } while (--op); 192131380Stjr from = out - dist; /* rest from output */ 193131380Stjr } 194131380Stjr } 195131380Stjr else if (write < op) { /* wrap around window */ 196131380Stjr from += wsize + write - op; 197131380Stjr op -= write; 198131380Stjr if (op < len) { /* some from end of window */ 199131380Stjr len -= op; 200131380Stjr do { 201131380Stjr PUP(out) = PUP(from); 202131380Stjr } while (--op); 203131380Stjr from = window - OFF; 204131380Stjr if (write < len) { /* some from start of window */ 205131380Stjr op = write; 206131380Stjr len -= op; 207131380Stjr do { 208131380Stjr PUP(out) = PUP(from); 209131380Stjr } while (--op); 210131380Stjr from = out - dist; /* rest from output */ 211131380Stjr } 212131380Stjr } 213131380Stjr } 214131380Stjr else { /* contiguous in window */ 215131380Stjr from += write - op; 216131380Stjr if (op < len) { /* some from window */ 217131380Stjr len -= op; 218131380Stjr do { 219131380Stjr PUP(out) = PUP(from); 220131380Stjr } while (--op); 221131380Stjr from = out - dist; /* rest from output */ 222131380Stjr } 223131380Stjr } 224131380Stjr while (len > 2) { 225131380Stjr PUP(out) = PUP(from); 226131380Stjr PUP(out) = PUP(from); 227131380Stjr PUP(out) = PUP(from); 228131380Stjr len -= 3; 229131380Stjr } 230131380Stjr if (len) { 231131380Stjr PUP(out) = PUP(from); 232131380Stjr if (len > 1) 233131380Stjr PUP(out) = PUP(from); 234131380Stjr } 235131380Stjr } 236131380Stjr else { 237131380Stjr from = out - dist; /* copy direct from output */ 238131380Stjr do { /* minimum length is three */ 239131380Stjr PUP(out) = PUP(from); 240131380Stjr PUP(out) = PUP(from); 241131380Stjr PUP(out) = PUP(from); 242131380Stjr len -= 3; 243131380Stjr } while (len > 2); 244131380Stjr if (len) { 245131380Stjr PUP(out) = PUP(from); 246131380Stjr if (len > 1) 247131380Stjr PUP(out) = PUP(from); 248131380Stjr } 249131380Stjr } 250131380Stjr } 251131380Stjr else if ((op & 64) == 0) { /* 2nd level distance code */ 252131380Stjr this = dcode[this.val + (hold & ((1U << op) - 1))]; 253131380Stjr goto dodist; 254131380Stjr } 255131380Stjr else { 256131380Stjr strm->msg = (char *)"invalid distance code"; 257131380Stjr state->mode = BAD; 258131380Stjr break; 259131380Stjr } 260131380Stjr } 261131380Stjr else if ((op & 64) == 0) { /* 2nd level length code */ 262131380Stjr this = lcode[this.val + (hold & ((1U << op) - 1))]; 263131380Stjr goto dolen; 264131380Stjr } 265131380Stjr else if (op & 32) { /* end-of-block */ 266131380Stjr Tracevv((stderr, "inflate: end of block\n")); 267131380Stjr state->mode = TYPE; 26817651Speter break; 26917651Speter } 270131380Stjr else { 271131380Stjr strm->msg = (char *)"invalid literal/length code"; 272131380Stjr state->mode = BAD; 273131380Stjr break; 274131380Stjr } 275131380Stjr } while (in < last && out < end); 27617651Speter 277131380Stjr /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ 278131380Stjr len = bits >> 3; 279131380Stjr in -= len; 280131380Stjr bits -= len << 3; 281131380Stjr hold &= (1U << bits) - 1; 282131380Stjr 283131380Stjr /* update state and return */ 284131380Stjr strm->next_in = in + OFF; 285131380Stjr strm->next_out = out + OFF; 286131380Stjr strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); 287131380Stjr strm->avail_out = (unsigned)(out < end ? 288131380Stjr 257 + (end - out) : 257 - (out - end)); 289131380Stjr state->hold = hold; 290131380Stjr state->bits = bits; 291131380Stjr return; 29217651Speter} 293131380Stjr 294131380Stjr/* 295131380Stjr inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): 296131380Stjr - Using bit fields for code structure 297131380Stjr - Different op definition to avoid & for extra bits (do & for table bits) 298131380Stjr - Three separate decoding do-loops for direct, window, and write == 0 299131380Stjr - Special case for distance > 1 copies to do overlapped load and store copy 300131380Stjr - Explicit branch predictions (based on measured branch probabilities) 301131380Stjr - Deferring match copy and interspersed it with decoding subsequent codes 302131380Stjr - Swapping literal/length else 303131380Stjr - Swapping window/direct else 304131380Stjr - Larger unrolled copy loops (three is about right) 305131380Stjr - Moving len -= 3 statement into middle of loop 306131380Stjr */ 307131380Stjr 308131380Stjr#endif /* !ASMINF */ 309