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
6 #include <linux/zutil.h>
7 #include <asm/unaligned.h>
8 #include <asm/byteorder.h>
15 /* Allow machine dependent optimization for post-increment or pre-increment.
16 Based on testing to date,
17 Pre-increment preferred for:
19 - MIPS R5000 (Randers-Pehrson)
20 Post-increment preferred for:
22 No measurable difference:
23 - Pentium III (Anderson)
28 # define PUP(a) *(a)++
29 # define UP_UNALIGNED(a) get_unaligned((a)++)
32 # define PUP(a) *++(a)
33 # define UP_UNALIGNED(a) get_unaligned(++(a))
37 Decode literal, length, and distance codes and write out the resulting
38 literal and match bytes until either not enough input or output is
39 available, an end-of-block is encountered, or a data error is encountered.
40 When large enough input and output buffers are supplied to inflate(), for
41 example, a 16K input buffer and a 64K output buffer, more than 95% of the
42 inflate execution time is spent in this routine.
48 strm->avail_out >= 258
49 start >= strm->avail_out
52 On return, state->mode is one of:
54 LEN -- ran out of enough output space or enough available input
55 TYPE -- reached end of block code, inflate() to interpret next block
56 BAD -- error in block data
60 - The maximum input bits used by a length/distance pair is 15 bits for the
61 length code, 5 bits for the length extra, 15 bits for the distance code,
62 and 13 bits for the distance extra. This totals 48 bits, or six bytes.
63 Therefore if strm->avail_in >= 6, then there is enough input to avoid
64 checking for available input while decoding.
66 - The maximum bytes that a single length/distance pair can output is 258
67 bytes, which is the maximum length that can be coded. inflate_fast()
68 requires strm->avail_out >= 258 for each loop to avoid checking for
71 - @start: inflate()'s starting value for strm->avail_out
73 void inflate_fast(z_streamp strm, unsigned start)
75 struct inflate_state *state;
76 const unsigned char *in; /* local strm->next_in */
77 const unsigned char *last; /* while in < last, enough input available */
78 unsigned char *out; /* local strm->next_out */
79 unsigned char *beg; /* inflate()'s initial strm->next_out */
80 unsigned char *end; /* while out < end, enough space available */
82 unsigned dmax; /* maximum distance from zlib header */
84 unsigned wsize; /* window size or zero if not using window */
85 unsigned whave; /* valid bytes in the window */
86 unsigned write; /* window write index */
87 unsigned char *window; /* allocated sliding window, if wsize != 0 */
88 unsigned long hold; /* local strm->hold */
89 unsigned bits; /* local strm->bits */
90 code const *lcode; /* local strm->lencode */
91 code const *dcode; /* local strm->distcode */
92 unsigned lmask; /* mask for first level of length codes */
93 unsigned dmask; /* mask for first level of distance codes */
94 code this; /* retrieved table entry */
95 unsigned op; /* code bits, operation, extra bits, or */
96 /* window position, window bytes to copy */
97 unsigned len; /* match length, unused bytes */
98 unsigned dist; /* match distance */
99 unsigned char *from; /* where to copy match from */
101 /* copy state to local variables */
102 state = (struct inflate_state *)strm->state;
103 in = strm->next_in - OFF;
104 last = in + (strm->avail_in - 5);
105 out = strm->next_out - OFF;
106 beg = out - (start - strm->avail_out);
107 end = out + (strm->avail_out - 257);
108 #ifdef INFLATE_STRICT
111 wsize = state->wsize;
112 whave = state->whave;
113 write = state->write;
114 window = state->window;
117 lcode = state->lencode;
118 dcode = state->distcode;
119 lmask = (1U << state->lenbits) - 1;
120 dmask = (1U << state->distbits) - 1;
122 /* decode literals and length/distances until end-of-block or not enough
123 input data or output space */
126 hold += (unsigned long)(PUP(in)) << bits;
128 hold += (unsigned long)(PUP(in)) << bits;
131 this = lcode[hold & lmask];
133 op = (unsigned)(this.bits);
136 op = (unsigned)(this.op);
137 if (op == 0) { /* literal */
138 PUP(out) = (unsigned char)(this.val);
140 else if (op & 16) { /* length base */
141 len = (unsigned)(this.val);
142 op &= 15; /* number of extra bits */
145 hold += (unsigned long)(PUP(in)) << bits;
148 len += (unsigned)hold & ((1U << op) - 1);
153 hold += (unsigned long)(PUP(in)) << bits;
155 hold += (unsigned long)(PUP(in)) << bits;
158 this = dcode[hold & dmask];
160 op = (unsigned)(this.bits);
163 op = (unsigned)(this.op);
164 if (op & 16) { /* distance base */
165 dist = (unsigned)(this.val);
166 op &= 15; /* number of extra bits */
168 hold += (unsigned long)(PUP(in)) << bits;
171 hold += (unsigned long)(PUP(in)) << bits;
175 dist += (unsigned)hold & ((1U << op) - 1);
176 #ifdef INFLATE_STRICT
178 strm->msg = (char *)"invalid distance too far back";
185 op = (unsigned)(out - beg); /* max distance in output */
186 if (dist > op) { /* see if copy from window */
187 op = dist - op; /* distance back in window */
189 strm->msg = (char *)"invalid distance too far back";
194 if (write == 0) { /* very common case */
196 if (op < len) { /* some from window */
199 PUP(out) = PUP(from);
201 from = out - dist; /* rest from output */
204 else if (write < op) { /* wrap around window */
205 from += wsize + write - op;
207 if (op < len) { /* some from end of window */
210 PUP(out) = PUP(from);
213 if (write < len) { /* some from start of window */
217 PUP(out) = PUP(from);
219 from = out - dist; /* rest from output */
223 else { /* contiguous in window */
225 if (op < len) { /* some from window */
228 PUP(out) = PUP(from);
230 from = out - dist; /* rest from output */
234 PUP(out) = PUP(from);
235 PUP(out) = PUP(from);
236 PUP(out) = PUP(from);
240 PUP(out) = PUP(from);
242 PUP(out) = PUP(from);
246 unsigned short *sout;
249 from = out - dist; /* copy direct from output */
250 /* minimum length is three */
252 if (!((long)(out - 1 + OFF) & 1)) {
253 PUP(out) = PUP(from);
256 sout = (unsigned short *)(out - OFF);
258 unsigned short *sfrom;
260 sfrom = (unsigned short *)(from - OFF);
263 PUP(sout) = UP_UNALIGNED(sfrom);
265 out = (unsigned char *)sout + OFF;
266 from = (unsigned char *)sfrom + OFF;
267 } else { /* dist == 1 or dist == 2 */
268 unsigned short pat16;
270 pat16 = *(sout-2+2*OFF);
272 #if defined(__BIG_ENDIAN)
273 pat16 = (pat16 & 0xff) | ((pat16 & 0xff) << 8);
274 #elif defined(__LITTLE_ENDIAN)
275 pat16 = (pat16 & 0xff00) | ((pat16 & 0xff00) >> 8);
277 #error __BIG_ENDIAN nor __LITTLE_ENDIAN is defined
283 out = (unsigned char *)sout + OFF;
286 PUP(out) = PUP(from);
289 else if ((op & 64) == 0) { /* 2nd level distance code */
290 this = dcode[this.val + (hold & ((1U << op) - 1))];
294 strm->msg = (char *)"invalid distance code";
299 else if ((op & 64) == 0) { /* 2nd level length code */
300 this = lcode[this.val + (hold & ((1U << op) - 1))];
303 else if (op & 32) { /* end-of-block */
308 strm->msg = (char *)"invalid literal/length code";
312 } while (in < last && out < end);
314 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
318 hold &= (1U << bits) - 1;
320 /* update state and return */
321 strm->next_in = in + OFF;
322 strm->next_out = out + OFF;
323 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last));
324 strm->avail_out = (unsigned)(out < end ?
325 257 + (end - out) : 257 - (out - end));
332 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
333 - Using bit fields for code structure
334 - Different op definition to avoid & for extra bits (do & for table bits)
335 - Three separate decoding do-loops for direct, window, and write == 0
336 - Special case for distance > 1 copies to do overlapped load and store copy
337 - Explicit branch predictions (based on measured branch probabilities)
338 - Deferring match copy and interspersed it with decoding subsequent codes
339 - Swapping literal/length else
340 - Swapping window/direct else
341 - Larger unrolled copy loops (three is about right)
342 - Moving len -= 3 statement into middle of loop