d84560c076d83cfca8a0d2d19b6214ed1cac23ca
[linux-3.10.git] / lib / zlib_inflate / 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 <linux/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     - @start:   inflate()'s starting value for strm->avail_out
68  */
69 void inflate_fast(z_streamp strm, unsigned start)
70 {
71     struct inflate_state *state;
72     unsigned char *in;      /* local strm->next_in */
73     unsigned char *last;    /* while in < last, enough input available */
74     unsigned char *out;     /* local strm->next_out */
75     unsigned char *beg;     /* inflate()'s initial strm->next_out */
76     unsigned char *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 *window;  /* allocated sliding window, if wsize != 0 */
84     unsigned long hold;         /* local strm->hold */
85     unsigned bits;              /* local strm->bits */
86     code const *lcode;      /* local strm->lencode */
87     code const *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 *from;    /* where to copy match from */
96
97     /* copy state to local variables */
98     state = (struct inflate_state *)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             PUP(out) = (unsigned char)(this.val);
135         }
136         else if (op & 16) {                     /* length base */
137             len = (unsigned)(this.val);
138             op &= 15;                           /* number of extra bits */
139             if (op) {
140                 if (bits < op) {
141                     hold += (unsigned long)(PUP(in)) << bits;
142                     bits += 8;
143                 }
144                 len += (unsigned)hold & ((1U << op) - 1);
145                 hold >>= op;
146                 bits -= op;
147             }
148             if (bits < 15) {
149                 hold += (unsigned long)(PUP(in)) << bits;
150                 bits += 8;
151                 hold += (unsigned long)(PUP(in)) << bits;
152                 bits += 8;
153             }
154             this = dcode[hold & dmask];
155           dodist:
156             op = (unsigned)(this.bits);
157             hold >>= op;
158             bits -= op;
159             op = (unsigned)(this.op);
160             if (op & 16) {                      /* distance base */
161                 dist = (unsigned)(this.val);
162                 op &= 15;                       /* number of extra bits */
163                 if (bits < op) {
164                     hold += (unsigned long)(PUP(in)) << bits;
165                     bits += 8;
166                     if (bits < op) {
167                         hold += (unsigned long)(PUP(in)) << bits;
168                         bits += 8;
169                     }
170                 }
171                 dist += (unsigned)hold & ((1U << op) - 1);
172 #ifdef INFLATE_STRICT
173                 if (dist > dmax) {
174                     strm->msg = (char *)"invalid distance too far back";
175                     state->mode = BAD;
176                     break;
177                 }
178 #endif
179                 hold >>= op;
180                 bits -= op;
181                 op = (unsigned)(out - beg);     /* max distance in output */
182                 if (dist > op) {                /* see if copy from window */
183                     op = dist - op;             /* distance back in window */
184                     if (op > whave) {
185                         strm->msg = (char *)"invalid distance too far back";
186                         state->mode = BAD;
187                         break;
188                     }
189                     from = window - OFF;
190                     if (write == 0) {           /* very common case */
191                         from += wsize - op;
192                         if (op < len) {         /* some from window */
193                             len -= op;
194                             do {
195                                 PUP(out) = PUP(from);
196                             } while (--op);
197                             from = out - dist;  /* rest from output */
198                         }
199                     }
200                     else if (write < op) {      /* wrap around window */
201                         from += wsize + write - op;
202                         op -= write;
203                         if (op < len) {         /* some from end of window */
204                             len -= op;
205                             do {
206                                 PUP(out) = PUP(from);
207                             } while (--op);
208                             from = window - OFF;
209                             if (write < len) {  /* some from start of window */
210                                 op = write;
211                                 len -= op;
212                                 do {
213                                     PUP(out) = PUP(from);
214                                 } while (--op);
215                                 from = out - dist;      /* rest from output */
216                             }
217                         }
218                     }
219                     else {                      /* contiguous in window */
220                         from += write - op;
221                         if (op < len) {         /* some from window */
222                             len -= op;
223                             do {
224                                 PUP(out) = PUP(from);
225                             } while (--op);
226                             from = out - dist;  /* rest from output */
227                         }
228                     }
229                     while (len > 2) {
230                         PUP(out) = PUP(from);
231                         PUP(out) = PUP(from);
232                         PUP(out) = PUP(from);
233                         len -= 3;
234                     }
235                     if (len) {
236                         PUP(out) = PUP(from);
237                         if (len > 1)
238                             PUP(out) = PUP(from);
239                     }
240                 }
241                 else {
242                     from = out - dist;          /* copy direct from output */
243                     do {                        /* minimum length is three */
244                         PUP(out) = PUP(from);
245                         PUP(out) = PUP(from);
246                         PUP(out) = PUP(from);
247                         len -= 3;
248                     } while (len > 2);
249                     if (len) {
250                         PUP(out) = PUP(from);
251                         if (len > 1)
252                             PUP(out) = PUP(from);
253                     }
254                 }
255             }
256             else if ((op & 64) == 0) {          /* 2nd level distance code */
257                 this = dcode[this.val + (hold & ((1U << op) - 1))];
258                 goto dodist;
259             }
260             else {
261                 strm->msg = (char *)"invalid distance code";
262                 state->mode = BAD;
263                 break;
264             }
265         }
266         else if ((op & 64) == 0) {              /* 2nd level length code */
267             this = lcode[this.val + (hold & ((1U << op) - 1))];
268             goto dolen;
269         }
270         else if (op & 32) {                     /* end-of-block */
271             state->mode = TYPE;
272             break;
273         }
274         else {
275             strm->msg = (char *)"invalid literal/length code";
276             state->mode = BAD;
277             break;
278         }
279     } while (in < last && out < end);
280
281     /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
282     len = bits >> 3;
283     in -= len;
284     bits -= len << 3;
285     hold &= (1U << bits) - 1;
286
287     /* update state and return */
288     strm->next_in = in + OFF;
289     strm->next_out = out + OFF;
290     strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
291     strm->avail_out = (unsigned)(out < end ?
292                                  257 + (end - out) : 257 - (out - end));
293     state->hold = hold;
294     state->bits = bits;
295     return;
296 }
297
298 /*
299    inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
300    - Using bit fields for code structure
301    - Different op definition to avoid & for extra bits (do & for table bits)
302    - Three separate decoding do-loops for direct, window, and write == 0
303    - Special case for distance > 1 copies to do overlapped load and store copy
304    - Explicit branch predictions (based on measured branch probabilities)
305    - Deferring match copy and interspersed it with decoding subsequent codes
306    - Swapping literal/length else
307    - Swapping window/direct else
308    - Larger unrolled copy loops (three is about right)
309    - Moving len -= 3 statement into middle of loop
310  */
311
312 #endif /* !ASMINF */