Merge branch 'origtgz'
[alioth/cvs.git] / zlib / inffast.c
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  */
67 void inflate_fast(strm, start)
68 z_streamp strm;
69 unsigned 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 */