[337] | 1 | /* adler32.c -- compute the Adler-32 checksum of a data stream
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| 2 | * Copyright (C) 1995-2011, 2016 Mark Adler
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| 3 | * For conditions of distribution and use, see copyright notice in zlib.h
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| 4 | */
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| 5 |
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| 6 | /* @(#) $Id$ */
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| 7 |
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| 8 | #include "zutil.h"
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| 9 |
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| 10 | local uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2));
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| 11 |
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| 12 | #define BASE 65521U /* largest prime smaller than 65536 */
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| 13 | #define NMAX 5552
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| 14 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
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| 15 |
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| 16 | #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
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| 17 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
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| 18 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
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| 19 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
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| 20 | #define DO16(buf) DO8(buf,0); DO8(buf,8);
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| 21 |
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| 22 | /* use NO_DIVIDE if your processor does not do division in hardware --
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| 23 | try it both ways to see which is faster */
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| 24 | #ifdef NO_DIVIDE
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| 25 | /* note that this assumes BASE is 65521, where 65536 % 65521 == 15
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| 26 | (thank you to John Reiser for pointing this out) */
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| 27 | # define CHOP(a) \
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| 28 | do { \
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| 29 | unsigned long tmp = a >> 16; \
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| 30 | a &= 0xffffUL; \
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| 31 | a += (tmp << 4) - tmp; \
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| 32 | } while (0)
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| 33 | # define MOD28(a) \
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| 34 | do { \
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| 35 | CHOP(a); \
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| 36 | if (a >= BASE) a -= BASE; \
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| 37 | } while (0)
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| 38 | # define MOD(a) \
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| 39 | do { \
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| 40 | CHOP(a); \
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| 41 | MOD28(a); \
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| 42 | } while (0)
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| 43 | # define MOD63(a) \
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| 44 | do { /* this assumes a is not negative */ \
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| 45 | z_off64_t tmp = a >> 32; \
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| 46 | a &= 0xffffffffL; \
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| 47 | a += (tmp << 8) - (tmp << 5) + tmp; \
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| 48 | tmp = a >> 16; \
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| 49 | a &= 0xffffL; \
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| 50 | a += (tmp << 4) - tmp; \
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| 51 | tmp = a >> 16; \
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| 52 | a &= 0xffffL; \
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| 53 | a += (tmp << 4) - tmp; \
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| 54 | if (a >= BASE) a -= BASE; \
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| 55 | } while (0)
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| 56 | #else
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| 57 | # define MOD(a) a %= BASE
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| 58 | # define MOD28(a) a %= BASE
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| 59 | # define MOD63(a) a %= BASE
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| 60 | #endif
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| 61 |
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| 62 | /* ========================================================================= */
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| 63 | uLong ZEXPORT adler32_z(adler, buf, len)
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| 64 | uLong adler;
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| 65 | const Bytef *buf;
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| 66 | z_size_t len;
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| 67 | {
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| 68 | unsigned long sum2;
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| 69 | unsigned n;
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| 70 |
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| 71 | /* split Adler-32 into component sums */
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| 72 | sum2 = (adler >> 16) & 0xffff;
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| 73 | adler &= 0xffff;
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| 74 |
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| 75 | /* in case user likes doing a byte at a time, keep it fast */
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| 76 | if (len == 1) {
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| 77 | adler += buf[0];
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| 78 | if (adler >= BASE)
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| 79 | adler -= BASE;
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| 80 | sum2 += adler;
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| 81 | if (sum2 >= BASE)
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| 82 | sum2 -= BASE;
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| 83 | return adler | (sum2 << 16);
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| 84 | }
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| 85 |
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| 86 | /* initial Adler-32 value (deferred check for len == 1 speed) */
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| 87 | if (buf == Z_NULL)
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| 88 | return 1L;
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| 89 |
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| 90 | /* in case short lengths are provided, keep it somewhat fast */
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| 91 | if (len < 16) {
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| 92 | while (len--) {
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| 93 | adler += *buf++;
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| 94 | sum2 += adler;
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| 95 | }
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| 96 | if (adler >= BASE)
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| 97 | adler -= BASE;
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| 98 | MOD28(sum2); /* only added so many BASE's */
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| 99 | return adler | (sum2 << 16);
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| 100 | }
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| 101 |
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| 102 | /* do length NMAX blocks -- requires just one modulo operation */
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| 103 | while (len >= NMAX) {
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| 104 | len -= NMAX;
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| 105 | n = NMAX / 16; /* NMAX is divisible by 16 */
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| 106 | do {
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| 107 | DO16(buf); /* 16 sums unrolled */
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| 108 | buf += 16;
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| 109 | } while (--n);
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| 110 | MOD(adler);
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| 111 | MOD(sum2);
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| 112 | }
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| 113 |
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| 114 | /* do remaining bytes (less than NMAX, still just one modulo) */
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| 115 | if (len) { /* avoid modulos if none remaining */
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| 116 | while (len >= 16) {
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| 117 | len -= 16;
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| 118 | DO16(buf);
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| 119 | buf += 16;
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| 120 | }
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| 121 | while (len--) {
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| 122 | adler += *buf++;
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| 123 | sum2 += adler;
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| 124 | }
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| 125 | MOD(adler);
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| 126 | MOD(sum2);
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| 127 | }
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| 128 |
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| 129 | /* return recombined sums */
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| 130 | return adler | (sum2 << 16);
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| 131 | }
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| 132 |
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| 133 | /* ========================================================================= */
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| 134 | uLong ZEXPORT adler32(adler, buf, len)
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| 135 | uLong adler;
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| 136 | const Bytef *buf;
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| 137 | uInt len;
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| 138 | {
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| 139 | return adler32_z(adler, buf, len);
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| 140 | }
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| 141 |
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| 142 | /* ========================================================================= */
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| 143 | local uLong adler32_combine_(adler1, adler2, len2)
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| 144 | uLong adler1;
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| 145 | uLong adler2;
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| 146 | z_off64_t len2;
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| 147 | {
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| 148 | unsigned long sum1;
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| 149 | unsigned long sum2;
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| 150 | unsigned rem;
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| 151 |
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| 152 | /* for negative len, return invalid adler32 as a clue for debugging */
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| 153 | if (len2 < 0)
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| 154 | return 0xffffffffUL;
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| 155 |
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| 156 | /* the derivation of this formula is left as an exercise for the reader */
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| 157 | MOD63(len2); /* assumes len2 >= 0 */
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| 158 | rem = (unsigned)len2;
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| 159 | sum1 = adler1 & 0xffff;
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| 160 | sum2 = rem * sum1;
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| 161 | MOD(sum2);
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| 162 | sum1 += (adler2 & 0xffff) + BASE - 1;
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| 163 | sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
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| 164 | if (sum1 >= BASE) sum1 -= BASE;
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| 165 | if (sum1 >= BASE) sum1 -= BASE;
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| 166 | if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1);
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| 167 | if (sum2 >= BASE) sum2 -= BASE;
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| 168 | return sum1 | (sum2 << 16);
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| 169 | }
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| 170 |
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| 171 | /* ========================================================================= */
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| 172 | uLong ZEXPORT adler32_combine(adler1, adler2, len2)
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| 173 | uLong adler1;
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| 174 | uLong adler2;
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| 175 | z_off_t len2;
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| 176 | {
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| 177 | return adler32_combine_(adler1, adler2, len2);
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| 178 | }
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| 179 |
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| 180 | uLong ZEXPORT adler32_combine64(adler1, adler2, len2)
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| 181 | uLong adler1;
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| 182 | uLong adler2;
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| 183 | z_off64_t len2;
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| 184 | {
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| 185 | return adler32_combine_(adler1, adler2, len2);
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| 186 | }
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