1 /* inffast.c -- fast decoding
2 * Copyright (C) 1995-2008, 2010, 2013 Mark Adler
3 * For conditions of distribution and use, see copyright notice in zlib.h
13 /* Allow machine dependent optimization for post-increment or pre-increment.
14 Based on testing to date,
15 Pre-increment preferred for:
17 - MIPS R5000 (Randers-Pehrson)
18 Post-increment preferred for:
20 No measurable difference:
21 - Pentium III (Anderson)
26 # define PUP(a) *(a)++
29 # define PUP(a) *++(a)
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.
44 strm->avail_out >= 258
45 start >= strm->avail_out
48 On return, state->mode is one of:
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
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.
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
67 void ZLIB_INTERNAL
inflate_fast(strm
, start
)
69 unsigned start
; /* inflate()'s starting value for strm->avail_out */
71 struct inflate_state FAR
*state
;
72 z_const
unsigned char FAR
*in
; /* local strm->next_in */
73 z_const
unsigned char FAR
*last
; /* have enough input while in < last */
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 */
78 unsigned dmax
; /* maximum distance from zlib header */
80 unsigned wsize
; /* window size or zero if not using window */
81 unsigned whave
; /* valid bytes in the window */
82 unsigned wnext
; /* 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 here
; /* 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 */
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
107 wsize
= state
->wsize
;
108 whave
= state
->whave
;
109 wnext
= state
->wnext
;
110 window
= state
->window
;
113 lcode
= state
->lencode
;
114 dcode
= state
->distcode
;
115 lmask
= (1U << state
->lenbits
) - 1;
116 dmask
= (1U << state
->distbits
) - 1;
118 /* decode literals and length/distances until end-of-block or not enough
119 input data or output space */
122 hold
+= (unsigned long)(PUP(in
)) << bits
;
124 hold
+= (unsigned long)(PUP(in
)) << bits
;
127 here
= lcode
[hold
& lmask
];
129 op
= (unsigned)(here
.bits
);
132 op
= (unsigned)(here
.op
);
133 if (op
== 0) { /* literal */
134 Tracevv((stderr
, here
.val
>= 0x20 && here
.val
< 0x7f ?
135 "inflate: literal '%c'\n" :
136 "inflate: literal 0x%02x\n", here
.val
));
137 PUP(out
) = (unsigned char)(here
.val
);
139 else if (op
& 16) { /* length base */
140 len
= (unsigned)(here
.val
);
141 op
&= 15; /* number of extra bits */
144 hold
+= (unsigned long)(PUP(in
)) << bits
;
147 len
+= (unsigned)hold
& ((1U << op
) - 1);
151 Tracevv((stderr
, "inflate: length %u\n", len
));
153 hold
+= (unsigned long)(PUP(in
)) << bits
;
155 hold
+= (unsigned long)(PUP(in
)) << bits
;
158 here
= dcode
[hold
& dmask
];
160 op
= (unsigned)(here
.bits
);
163 op
= (unsigned)(here
.op
);
164 if (op
& 16) { /* distance base */
165 dist
= (unsigned)(here
.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 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 */
192 (char *)"invalid distance too far back";
196 #ifdef INFLATE_ALLOW_INVALID_DISTANCE_TOOFAR_ARRR
197 if (len
<= op
- whave
) {
206 } while (--op
> whave
);
210 PUP(out
) = PUP(from
);
217 if (wnext
== 0) { /* very common case */
219 if (op
< len
) { /* some from window */
222 PUP(out
) = PUP(from
);
224 from
= out
- dist
; /* rest from output */
227 else if (wnext
< op
) { /* wrap around window */
228 from
+= wsize
+ wnext
- op
;
230 if (op
< len
) { /* some from end of window */
233 PUP(out
) = PUP(from
);
236 if (wnext
< len
) { /* some from start of window */
240 PUP(out
) = PUP(from
);
242 from
= out
- dist
; /* rest from output */
246 else { /* contiguous in window */
248 if (op
< len
) { /* some from window */
251 PUP(out
) = PUP(from
);
253 from
= out
- dist
; /* rest from output */
257 PUP(out
) = PUP(from
);
258 PUP(out
) = PUP(from
);
259 PUP(out
) = PUP(from
);
263 PUP(out
) = PUP(from
);
265 PUP(out
) = PUP(from
);
269 from
= out
- dist
; /* copy direct from output */
270 do { /* minimum length is three */
271 PUP(out
) = PUP(from
);
272 PUP(out
) = PUP(from
);
273 PUP(out
) = PUP(from
);
277 PUP(out
) = PUP(from
);
279 PUP(out
) = PUP(from
);
283 else if ((op
& 64) == 0) { /* 2nd level distance code */
284 here
= dcode
[here
.val
+ (hold
& ((1U << op
) - 1))];
288 strm
->msg
= (char *)"invalid distance code";
293 else if ((op
& 64) == 0) { /* 2nd level length code */
294 here
= lcode
[here
.val
+ (hold
& ((1U << op
) - 1))];
297 else if (op
& 32) { /* end-of-block */
298 Tracevv((stderr
, "inflate: end of block\n"));
303 strm
->msg
= (char *)"invalid literal/length code";
307 } while (in
< last
&& out
< end
);
309 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */
313 hold
&= (1U << bits
) - 1;
315 /* update state and return */
316 strm
->next_in
= in
+ OFF
;
317 strm
->next_out
= out
+ OFF
;
318 strm
->avail_in
= (unsigned)(in
< last
? 5 + (last
- in
) : 5 - (in
- last
));
319 strm
->avail_out
= (unsigned)(out
< end
?
320 257 + (end
- out
) : 257 - (out
- end
));
327 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe):
328 - Using bit fields for code structure
329 - Different op definition to avoid & for extra bits (do & for table bits)
330 - Three separate decoding do-loops for direct, window, and wnext == 0
331 - Special case for distance > 1 copies to do overlapped load and store copy
332 - Explicit branch predictions (based on measured branch probabilities)
333 - Deferring match copy and interspersed it with decoding subsequent codes
334 - Swapping literal/length else
335 - Swapping window/direct else
336 - Larger unrolled copy loops (three is about right)
337 - Moving len -= 3 statement into middle of loop
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