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/StormLib/stormlib/zlib/inffast.c

http://ghostcb.googlecode.com/
C | 318 lines | 239 code | 10 blank | 69 comment | 47 complexity | 962b35b2eed3bf72d26eedd0f68e16a3 MD5 | raw file
  1/* inffast.c -- fast decoding
  2 * Copyright (C) 1995-2004 Mark Adler
  3 * For conditions of distribution and use, see copyright notice in zlib.h
  4 */
  5
  6#include "zutil.h"
  7#include "inftrees.h"
  8#include "inflate.h"
  9#include "inffast.h"
 10
 11#ifndef ASMINF
 12
 13/* Allow machine dependent optimization for post-increment or pre-increment.
 14   Based on testing to date,
 15   Pre-increment preferred for:
 16   - PowerPC G3 (Adler)
 17   - MIPS R5000 (Randers-Pehrson)
 18   Post-increment preferred for:
 19   - none
 20   No measurable difference:
 21   - Pentium III (Anderson)
 22   - M68060 (Nikl)
 23 */
 24#ifdef POSTINC
 25#  define OFF 0
 26#  define PUP(a) *(a)++
 27#else
 28#  define OFF 1
 29#  define PUP(a) *++(a)
 30#endif
 31
 32/*
 33   Decode literal, length, and distance codes and write out the resulting
 34   literal and match bytes until either not enough input or output is
 35   available, an end-of-block is encountered, or a data error is encountered.
 36   When large enough input and output buffers are supplied to inflate(), for
 37   example, a 16K input buffer and a 64K output buffer, more than 95% of the
 38   inflate execution time is spent in this routine.
 39
 40   Entry assumptions:
 41
 42        state->mode == LEN
 43        strm->avail_in >= 6
 44        strm->avail_out >= 258
 45        start >= strm->avail_out
 46        state->bits < 8
 47
 48   On return, state->mode is one of:
 49
 50        LEN -- ran out of enough output space or enough available input
 51        TYPE -- reached end of block code, inflate() to interpret next block
 52        BAD -- error in block data
 53
 54   Notes:
 55
 56    - The maximum input bits used by a length/distance pair is 15 bits for the
 57      length code, 5 bits for the length extra, 15 bits for the distance code,
 58      and 13 bits for the distance extra.  This totals 48 bits, or six bytes.
 59      Therefore if strm->avail_in >= 6, then there is enough input to avoid
 60      checking for available input while decoding.
 61
 62    - The maximum bytes that a single length/distance pair can output is 258
 63      bytes, which is the maximum length that can be coded.  inflate_fast()
 64      requires strm->avail_out >= 258 for each loop to avoid checking for
 65      output space.
 66 */
 67void inflate_fast(strm, start)
 68z_streamp strm;
 69unsigned start;         /* inflate()'s starting value for strm->avail_out */
 70{
 71    struct inflate_state FAR *state;
 72    unsigned char FAR *in;      /* local strm->next_in */
 73    unsigned char FAR *last;    /* while in < last, enough input available */
 74    unsigned char FAR *out;     /* local strm->next_out */
 75    unsigned char FAR *beg;     /* inflate()'s initial strm->next_out */
 76    unsigned char FAR *end;     /* while out < end, enough space available */
 77#ifdef INFLATE_STRICT
 78    unsigned dmax;              /* maximum distance from zlib header */
 79#endif
 80    unsigned wsize;             /* window size or zero if not using window */
 81    unsigned whave;             /* valid bytes in the window */
 82    unsigned write;             /* window write index */
 83    unsigned char FAR *window;  /* allocated sliding window, if wsize != 0 */
 84    unsigned long hold;         /* local strm->hold */
 85    unsigned bits;              /* local strm->bits */
 86    code const FAR *lcode;      /* local strm->lencode */
 87    code const FAR *dcode;      /* local strm->distcode */
 88    unsigned lmask;             /* mask for first level of length codes */
 89    unsigned dmask;             /* mask for first level of distance codes */
 90    code this;                  /* retrieved table entry */
 91    unsigned op;                /* code bits, operation, extra bits, or */
 92                                /*  window position, window bytes to copy */
 93    unsigned len;               /* match length, unused bytes */
 94    unsigned dist;              /* match distance */
 95    unsigned char FAR *from;    /* where to copy match from */
 96
 97    /* copy state to local variables */
 98    state = (struct inflate_state FAR *)strm->state;
 99    in = strm->next_in - OFF;
100    last = in + (strm->avail_in - 5);
101    out = strm->next_out - OFF;
102    beg = out - (start - strm->avail_out);
103    end = out + (strm->avail_out - 257);
104#ifdef INFLATE_STRICT
105    dmax = state->dmax;
106#endif
107    wsize = state->wsize;
108    whave = state->whave;
109    write = state->write;
110    window = state->window;
111    hold = state->hold;
112    bits = state->bits;
113    lcode = state->lencode;
114    dcode = state->distcode;
115    lmask = (1U << state->lenbits) - 1;
116    dmask = (1U << state->distbits) - 1;
117
118    /* decode literals and length/distances until end-of-block or not enough
119       input data or output space */
120    do {
121        if (bits < 15) {
122            hold += (unsigned long)(PUP(in)) << bits;
123            bits += 8;
124            hold += (unsigned long)(PUP(in)) << bits;
125            bits += 8;
126        }
127        this = lcode[hold & lmask];
128      dolen:
129        op = (unsigned)(this.bits);
130        hold >>= op;
131        bits -= op;
132        op = (unsigned)(this.op);
133        if (op == 0) {                          /* literal */
134            Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ?
135                    "inflate:         literal '%c'\n" :
136                    "inflate:         literal 0x%02x\n", this.val));
137            PUP(out) = (unsigned char)(this.val);
138        }
139        else if (op & 16) {                     /* length base */
140            len = (unsigned)(this.val);
141            op &= 15;                           /* number of extra bits */
142            if (op) {
143                if (bits < op) {
144                    hold += (unsigned long)(PUP(in)) << bits;
145                    bits += 8;
146                }
147                len += (unsigned)hold & ((1U << op) - 1);
148                hold >>= op;
149                bits -= op;
150            }
151            Tracevv((stderr, "inflate:         length %u\n", len));
152            if (bits < 15) {
153                hold += (unsigned long)(PUP(in)) << bits;
154                bits += 8;
155                hold += (unsigned long)(PUP(in)) << bits;
156                bits += 8;
157            }
158            this = dcode[hold & dmask];
159          dodist:
160            op = (unsigned)(this.bits);
161            hold >>= op;
162            bits -= op;
163            op = (unsigned)(this.op);
164            if (op & 16) {                      /* distance base */
165                dist = (unsigned)(this.val);
166                op &= 15;                       /* number of extra bits */
167                if (bits < op) {
168                    hold += (unsigned long)(PUP(in)) << bits;
169                    bits += 8;
170                    if (bits < op) {
171                        hold += (unsigned long)(PUP(in)) << bits;
172                        bits += 8;
173                    }
174                }
175                dist += (unsigned)hold & ((1U << op) - 1);
176#ifdef INFLATE_STRICT
177                if (dist > dmax) {
178                    strm->msg = (char *)"invalid distance too far back";
179                    state->mode = BAD;
180                    break;
181                }
182#endif
183                hold >>= op;
184                bits -= op;
185                Tracevv((stderr, "inflate:         distance %u\n", dist));
186                op = (unsigned)(out - beg);     /* max distance in output */
187                if (dist > op) {                /* see if copy from window */
188                    op = dist - op;             /* distance back in window */
189                    if (op > whave) {
190                        strm->msg = (char *)"invalid distance too far back";
191                        state->mode = BAD;
192                        break;
193                    }
194                    from = window - OFF;
195                    if (write == 0) {           /* very common case */
196                        from += wsize - op;
197                        if (op < len) {         /* some from window */
198                            len -= op;
199                            do {
200                                PUP(out) = PUP(from);
201                            } while (--op);
202                            from = out - dist;  /* rest from output */
203                        }
204                    }
205                    else if (write < op) {      /* wrap around window */
206                        from += wsize + write - op;
207                        op -= write;
208                        if (op < len) {         /* some from end of window */
209                            len -= op;
210                            do {
211                                PUP(out) = PUP(from);
212                            } while (--op);
213                            from = window - OFF;
214                            if (write < len) {  /* some from start of window */
215                                op = write;
216                                len -= op;
217                                do {
218                                    PUP(out) = PUP(from);
219                                } while (--op);
220                                from = out - dist;      /* rest from output */
221                            }
222                        }
223                    }
224                    else {                      /* contiguous in window */
225                        from += write - op;
226                        if (op < len) {         /* some from window */
227                            len -= op;
228                            do {
229                                PUP(out) = PUP(from);
230                            } while (--op);
231                            from = out - dist;  /* rest from output */
232                        }
233                    }
234                    while (len > 2) {
235                        PUP(out) = PUP(from);
236                        PUP(out) = PUP(from);
237                        PUP(out) = PUP(from);
238                        len -= 3;
239                    }
240                    if (len) {
241                        PUP(out) = PUP(from);
242                        if (len > 1)
243                            PUP(out) = PUP(from);
244                    }
245                }
246                else {
247                    from = out - dist;          /* copy direct from output */
248                    do {                        /* minimum length is three */
249                        PUP(out) = PUP(from);
250                        PUP(out) = PUP(from);
251                        PUP(out) = PUP(from);
252                        len -= 3;
253                    } while (len > 2);
254                    if (len) {
255                        PUP(out) = PUP(from);
256                        if (len > 1)
257                            PUP(out) = PUP(from);
258                    }
259                }
260            }
261            else if ((op & 64) == 0) {          /* 2nd level distance code */
262                this = dcode[this.val + (hold & ((1U << op) - 1))];
263                goto dodist;
264            }
265            else {
266                strm->msg = (char *)"invalid distance code";
267                state->mode = BAD;
268                break;
269            }
270        }
271        else if ((op & 64) == 0) {              /* 2nd level length code */
272            this = lcode[this.val + (hold & ((1U << op) - 1))];
273            goto dolen;
274        }
275        else if (op & 32) {                     /* end-of-block */
276            Tracevv((stderr, "inflate:         end of block\n"));
277            state->mode = TYPE;
278            break;
279        }
280        else {
281            strm->msg = (char *)"invalid literal/length code";
282            state->mode = BAD;
283            break;
284        }
285    } while (in < last && out < end);
286
287    /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
288    len = bits >> 3;
289    in -= len;
290    bits -= len << 3;
291    hold &= (1U << bits) - 1;
292
293    /* update state and return */
294    strm->next_in = in + OFF;
295    strm->next_out = out + OFF;
296    strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
297    strm->avail_out = (unsigned)(out < end ?
298                                 257 + (end - out) : 257 - (out - end));
299    state->hold = hold;
300    state->bits = bits;
301    return;
302}
303
304/*
305   inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
306   - Using bit fields for code structure
307   - Different op definition to avoid & for extra bits (do & for table bits)
308   - Three separate decoding do-loops for direct, window, and write == 0
309   - Special case for distance > 1 copies to do overlapped load and store copy
310   - Explicit branch predictions (based on measured branch probabilities)
311   - Deferring match copy and interspersed it with decoding subsequent codes
312   - Swapping literal/length else
313   - Swapping window/direct else
314   - Larger unrolled copy loops (three is about right)
315   - Moving len -= 3 statement into middle of loop
316 */
317
318#endif /* !ASMINF */