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comparison zlib/inffast.c @ 3:5a977ccbc7a9 default tip

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author darius
date Sat, 06 Dec 1997 05:41:29 +0000
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2:fba0b6e6cdc7 3:5a977ccbc7a9
1 /* inffast.c -- process literals and length/distance pairs fast
2 * Copyright (C) 1995 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 "infutil.h"
9 #include "inffast.h"
10
11 struct inflate_codes_state {int dummy;}; /* for buggy compilers */
12
13 /* simplify the use of the inflate_huft type with some defines */
14 #define base more.Base
15 #define next more.Next
16 #define exop word.what.Exop
17 #define bits word.what.Bits
18
19 /* macros for bit input with no checking and for returning unused bytes */
20 #ifdef DEBUG
21 # undef NEXTBYTE
22 # define NEXTBYTE (n--?0:fprintf(stderr,"inffast underrun\n"),*p++)
23 #endif
24 #define GRABBITS(j) {while(k<(j)){b|=((uLong)NEXTBYTE)<<k;k+=8;}}
25 #define UNGRAB {n+=(c=k>>3);p-=c;k&=7;}
26
27 /* Called with number of bytes left to write in window at least 258
28 (the maximum string length) and number of input bytes available
29 at least ten. The ten bytes are six bytes for the longest length/
30 distance pair plus four bytes for overloading the bit buffer. */
31
32 int inflate_fast(bl, bd, tl, td, s, z)
33 uInt bl, bd;
34 inflate_huft *tl, *td;
35 struct inflate_blocks_state *s;
36 z_stream *z;
37 {
38 inflate_huft *t; /* temporary pointer */
39 int e; /* extra bits or operation */
40 uLong b; /* bit buffer */
41 uInt k; /* bits in bit buffer */
42 Byte *p; /* input data pointer */
43 uInt n; /* bytes available there */
44 Byte *q; /* output window write pointer */
45 uInt m; /* bytes to end of window or read pointer */
46 uInt ml; /* mask for literal/length tree */
47 uInt md; /* mask for distance tree */
48 uInt c; /* bytes to copy */
49 uInt d; /* distance back to copy from */
50 Byte *r; /* copy source pointer */
51
52 /* load input, output, bit values */
53 LOAD
54
55 /* initialize masks in registers */
56 ml = inflate_mask[bl];
57 md = inflate_mask[bd];
58
59 /* do until not enough input or output space for fast loop */
60 do { /* assume called with m >= 258 && n >= 10 */
61 /* get literal/length code */
62 GRABBITS(20) /* max bits for literal/length code */
63 if ((e = (t = tl + ((uInt)b & ml))->exop) < 0)
64 do {
65 if (e == -128)
66 {
67 z->msg = "invalid literal/length code";
68 UNGRAB
69 UPDATE
70 return Z_DATA_ERROR;
71 }
72 DUMPBITS(t->bits)
73 e = -e;
74 if (e & 64) /* end of block */
75 {
76 Tracevv((stderr, "inflate: * end of block\n"));
77 UNGRAB
78 UPDATE
79 return Z_STREAM_END;
80 }
81 } while ((e = (t = t->next + ((uInt)b & inflate_mask[e]))->exop) < 0);
82 DUMPBITS(t->bits)
83
84 /* process literal or length (end of block already trapped) */
85 if (e & 16) /* then it's a literal */
86 {
87 Tracevv((stderr, t->base >= 0x20 && t->base < 0x7f ?
88 "inflate: * literal '%c'\n" :
89 "inflate: * literal 0x%02x\n", t->base));
90 *q++ = (Byte)t->base;
91 m--;
92 }
93 else /* it's a length */
94 {
95 /* get length of block to copy (already have extra bits) */
96 c = t->base + ((uInt)b & inflate_mask[e]);
97 DUMPBITS(e);
98 Tracevv((stderr, "inflate: * length %u\n", c));
99
100 /* decode distance base of block to copy */
101 GRABBITS(15); /* max bits for distance code */
102 if ((e = (t = td + ((uInt)b & md))->exop) < 0)
103 do {
104 if (e == -128)
105 {
106 z->msg = "invalid distance code";
107 UNGRAB
108 UPDATE
109 return Z_DATA_ERROR;
110 }
111 DUMPBITS(t->bits)
112 e = -e;
113 } while ((e = (t = t->next + ((uInt)b & inflate_mask[e]))->exop) < 0);
114 DUMPBITS(t->bits)
115
116 /* get extra bits to add to distance base */
117 GRABBITS((uInt)e) /* get extra bits (up to 13) */
118 d = t->base + ((uInt)b & inflate_mask[e]);
119 DUMPBITS(e)
120 Tracevv((stderr, "inflate: * distance %u\n", d));
121
122 /* do the copy */
123 m -= c;
124 if ((uInt)(q - s->window) >= d) /* if offset before destination, */
125 { /* just copy */
126 r = q - d;
127 *q++ = *r++; c--; /* minimum count is three, */
128 *q++ = *r++; c--; /* so unroll loop a little */
129 do {
130 *q++ = *r++;
131 } while (--c);
132 }
133 else /* else offset after destination */
134 {
135 e = d - (q - s->window); /* bytes from offset to end */
136 r = s->end - e; /* pointer to offset */
137 if (c > (uInt)e) /* if source crosses, */
138 {
139 c -= e; /* copy to end of window */
140 do {
141 *q++ = *r++;
142 } while (--e);
143 r = s->window; /* copy rest from start of window */
144 }
145 do { /* copy all or what's left */
146 *q++ = *r++;
147 } while (--c);
148 }
149 }
150 } while (m >= 258 && n >= 10);
151
152 /* not enough input or output--restore pointers and return */
153 UNGRAB
154 UPDATE
155 return Z_OK;
156 }