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comparison mupdf-source/thirdparty/zlib/adler32.c @ 2:b50eed0cc0ef upstream

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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
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 #define BASE 65521U /* largest prime smaller than 65536 */
11 #define NMAX 5552
12 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
13
14 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
15 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
16 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
17 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
18 #define DO16(buf) DO8(buf,0); DO8(buf,8);
19
20 /* use NO_DIVIDE if your processor does not do division in hardware --
21 try it both ways to see which is faster */
22 #ifdef NO_DIVIDE
23 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
24 (thank you to John Reiser for pointing this out) */
25 # define CHOP(a) \
26 do { \
27 unsigned long tmp = a >> 16; \
28 a &= 0xffffUL; \
29 a += (tmp << 4) - tmp; \
30 } while (0)
31 # define MOD28(a) \
32 do { \
33 CHOP(a); \
34 if (a >= BASE) a -= BASE; \
35 } while (0)
36 # define MOD(a) \
37 do { \
38 CHOP(a); \
39 MOD28(a); \
40 } while (0)
41 # define MOD63(a) \
42 do { /* this assumes a is not negative */ \
43 z_off64_t tmp = a >> 32; \
44 a &= 0xffffffffL; \
45 a += (tmp << 8) - (tmp << 5) + tmp; \
46 tmp = a >> 16; \
47 a &= 0xffffL; \
48 a += (tmp << 4) - tmp; \
49 tmp = a >> 16; \
50 a &= 0xffffL; \
51 a += (tmp << 4) - tmp; \
52 if (a >= BASE) a -= BASE; \
53 } while (0)
54 #else
55 # define MOD(a) a %= BASE
56 # define MOD28(a) a %= BASE
57 # define MOD63(a) a %= BASE
58 #endif
59
60 /* ========================================================================= */
61 uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len) {
62 unsigned long sum2;
63 unsigned n;
64
65 /* split Adler-32 into component sums */
66 sum2 = (adler >> 16) & 0xffff;
67 adler &= 0xffff;
68
69 /* in case user likes doing a byte at a time, keep it fast */
70 if (len == 1) {
71 adler += buf[0];
72 if (adler >= BASE)
73 adler -= BASE;
74 sum2 += adler;
75 if (sum2 >= BASE)
76 sum2 -= BASE;
77 return adler | (sum2 << 16);
78 }
79
80 /* initial Adler-32 value (deferred check for len == 1 speed) */
81 if (buf == Z_NULL)
82 return 1L;
83
84 /* in case short lengths are provided, keep it somewhat fast */
85 if (len < 16) {
86 while (len--) {
87 adler += *buf++;
88 sum2 += adler;
89 }
90 if (adler >= BASE)
91 adler -= BASE;
92 MOD28(sum2); /* only added so many BASE's */
93 return adler | (sum2 << 16);
94 }
95
96 /* do length NMAX blocks -- requires just one modulo operation */
97 while (len >= NMAX) {
98 len -= NMAX;
99 n = NMAX / 16; /* NMAX is divisible by 16 */
100 do {
101 DO16(buf); /* 16 sums unrolled */
102 buf += 16;
103 } while (--n);
104 MOD(adler);
105 MOD(sum2);
106 }
107
108 /* do remaining bytes (less than NMAX, still just one modulo) */
109 if (len) { /* avoid modulos if none remaining */
110 while (len >= 16) {
111 len -= 16;
112 DO16(buf);
113 buf += 16;
114 }
115 while (len--) {
116 adler += *buf++;
117 sum2 += adler;
118 }
119 MOD(adler);
120 MOD(sum2);
121 }
122
123 /* return recombined sums */
124 return adler | (sum2 << 16);
125 }
126
127 /* ========================================================================= */
128 uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len) {
129 return adler32_z(adler, buf, len);
130 }
131
132 /* ========================================================================= */
133 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2) {
134 unsigned long sum1;
135 unsigned long sum2;
136 unsigned rem;
137
138 /* for negative len, return invalid adler32 as a clue for debugging */
139 if (len2 < 0)
140 return 0xffffffffUL;
141
142 /* the derivation of this formula is left as an exercise for the reader */
143 MOD63(len2); /* assumes len2 >= 0 */
144 rem = (unsigned)len2;
145 sum1 = adler1 & 0xffff;
146 sum2 = rem * sum1;
147 MOD(sum2);
148 sum1 += (adler2 & 0xffff) + BASE - 1;
149 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
150 if (sum1 >= BASE) sum1 -= BASE;
151 if (sum1 >= BASE) sum1 -= BASE;
152 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
153 if (sum2 >= BASE) sum2 -= BASE;
154 return sum1 | (sum2 << 16);
155 }
156
157 /* ========================================================================= */
158 uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2) {
159 return adler32_combine_(adler1, adler2, len2);
160 }
161
162 uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) {
163 return adler32_combine_(adler1, adler2, len2);
164 }