Mercurial > repos > blastem
comparison zlib/adler32.c @ 1530:00d788dac91a
Added support for reading gzipped ROMs
author | Michael Pavone <pavone@retrodev.com> |
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date | Fri, 23 Mar 2018 22:30:02 -0700 |
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1529:f7fe240a7da6 | 1530:00d788dac91a |
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1 /* adler32.c -- compute the Adler-32 checksum of a data stream | |
2 * Copyright (C) 1995-2011, 2016 Mark Adler | |
3 * For conditions of distribution and use, see copyright notice in zlib.h | |
4 */ | |
5 | |
6 /* @(#) $Id$ */ | |
7 | |
8 #include "zutil.h" | |
9 | |
10 local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); | |
11 | |
12 #define BASE 65521U /* largest prime smaller than 65536 */ | |
13 #define NMAX 5552 | |
14 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ | |
15 | |
16 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} | |
17 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); | |
18 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); | |
19 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); | |
20 #define DO16(buf) DO8(buf,0); DO8(buf,8); | |
21 | |
22 /* use NO_DIVIDE if your processor does not do division in hardware -- | |
23 try it both ways to see which is faster */ | |
24 #ifdef NO_DIVIDE | |
25 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 | |
26 (thank you to John Reiser for pointing this out) */ | |
27 # define CHOP(a) \ | |
28 do { \ | |
29 unsigned long tmp = a >> 16; \ | |
30 a &= 0xffffUL; \ | |
31 a += (tmp << 4) - tmp; \ | |
32 } while (0) | |
33 # define MOD28(a) \ | |
34 do { \ | |
35 CHOP(a); \ | |
36 if (a >= BASE) a -= BASE; \ | |
37 } while (0) | |
38 # define MOD(a) \ | |
39 do { \ | |
40 CHOP(a); \ | |
41 MOD28(a); \ | |
42 } while (0) | |
43 # define MOD63(a) \ | |
44 do { /* this assumes a is not negative */ \ | |
45 z_off64_t tmp = a >> 32; \ | |
46 a &= 0xffffffffL; \ | |
47 a += (tmp << 8) - (tmp << 5) + tmp; \ | |
48 tmp = a >> 16; \ | |
49 a &= 0xffffL; \ | |
50 a += (tmp << 4) - tmp; \ | |
51 tmp = a >> 16; \ | |
52 a &= 0xffffL; \ | |
53 a += (tmp << 4) - tmp; \ | |
54 if (a >= BASE) a -= BASE; \ | |
55 } while (0) | |
56 #else | |
57 # define MOD(a) a %= BASE | |
58 # define MOD28(a) a %= BASE | |
59 # define MOD63(a) a %= BASE | |
60 #endif | |
61 | |
62 /* ========================================================================= */ | |
63 uLong ZEXPORT adler32_z(adler, buf, len) | |
64 uLong adler; | |
65 const Bytef *buf; | |
66 z_size_t len; | |
67 { | |
68 unsigned long sum2; | |
69 unsigned n; | |
70 | |
71 /* split Adler-32 into component sums */ | |
72 sum2 = (adler >> 16) & 0xffff; | |
73 adler &= 0xffff; | |
74 | |
75 /* in case user likes doing a byte at a time, keep it fast */ | |
76 if (len == 1) { | |
77 adler += buf[0]; | |
78 if (adler >= BASE) | |
79 adler -= BASE; | |
80 sum2 += adler; | |
81 if (sum2 >= BASE) | |
82 sum2 -= BASE; | |
83 return adler | (sum2 << 16); | |
84 } | |
85 | |
86 /* initial Adler-32 value (deferred check for len == 1 speed) */ | |
87 if (buf == Z_NULL) | |
88 return 1L; | |
89 | |
90 /* in case short lengths are provided, keep it somewhat fast */ | |
91 if (len < 16) { | |
92 while (len--) { | |
93 adler += *buf++; | |
94 sum2 += adler; | |
95 } | |
96 if (adler >= BASE) | |
97 adler -= BASE; | |
98 MOD28(sum2); /* only added so many BASE's */ | |
99 return adler | (sum2 << 16); | |
100 } | |
101 | |
102 /* do length NMAX blocks -- requires just one modulo operation */ | |
103 while (len >= NMAX) { | |
104 len -= NMAX; | |
105 n = NMAX / 16; /* NMAX is divisible by 16 */ | |
106 do { | |
107 DO16(buf); /* 16 sums unrolled */ | |
108 buf += 16; | |
109 } while (--n); | |
110 MOD(adler); | |
111 MOD(sum2); | |
112 } | |
113 | |
114 /* do remaining bytes (less than NMAX, still just one modulo) */ | |
115 if (len) { /* avoid modulos if none remaining */ | |
116 while (len >= 16) { | |
117 len -= 16; | |
118 DO16(buf); | |
119 buf += 16; | |
120 } | |
121 while (len--) { | |
122 adler += *buf++; | |
123 sum2 += adler; | |
124 } | |
125 MOD(adler); | |
126 MOD(sum2); | |
127 } | |
128 | |
129 /* return recombined sums */ | |
130 return adler | (sum2 << 16); | |
131 } | |
132 | |
133 /* ========================================================================= */ | |
134 uLong ZEXPORT adler32(adler, buf, len) | |
135 uLong adler; | |
136 const Bytef *buf; | |
137 uInt len; | |
138 { | |
139 return adler32_z(adler, buf, len); | |
140 } | |
141 | |
142 /* ========================================================================= */ | |
143 local uLong adler32_combine_(adler1, adler2, len2) | |
144 uLong adler1; | |
145 uLong adler2; | |
146 z_off64_t len2; | |
147 { | |
148 unsigned long sum1; | |
149 unsigned long sum2; | |
150 unsigned rem; | |
151 | |
152 /* for negative len, return invalid adler32 as a clue for debugging */ | |
153 if (len2 < 0) | |
154 return 0xffffffffUL; | |
155 | |
156 /* the derivation of this formula is left as an exercise for the reader */ | |
157 MOD63(len2); /* assumes len2 >= 0 */ | |
158 rem = (unsigned)len2; | |
159 sum1 = adler1 & 0xffff; | |
160 sum2 = rem * sum1; | |
161 MOD(sum2); | |
162 sum1 += (adler2 & 0xffff) + BASE - 1; | |
163 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; | |
164 if (sum1 >= BASE) sum1 -= BASE; | |
165 if (sum1 >= BASE) sum1 -= BASE; | |
166 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); | |
167 if (sum2 >= BASE) sum2 -= BASE; | |
168 return sum1 | (sum2 << 16); | |
169 } | |
170 | |
171 /* ========================================================================= */ | |
172 uLong ZEXPORT adler32_combine(adler1, adler2, len2) | |
173 uLong adler1; | |
174 uLong adler2; | |
175 z_off_t len2; | |
176 { | |
177 return adler32_combine_(adler1, adler2, len2); | |
178 } | |
179 | |
180 uLong ZEXPORT adler32_combine64(adler1, adler2, len2) | |
181 uLong adler1; | |
182 uLong adler2; | |
183 z_off64_t len2; | |
184 { | |
185 return adler32_combine_(adler1, adler2, len2); | |
186 } |