| 1 | /* adler32.c -- compute the Adler-32 checksum of a data stream␊ |
| 2 | * Copyright (C) 1995-2007 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 local static␊ |
| 11 | ␊ |
| 12 | local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2);␊ |
| 13 | ␊ |
| 14 | #define BASE 65521UL /* largest prime smaller than 65536 */␊ |
| 15 | #define NMAX 5552␊ |
| 16 | /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */␊ |
| 17 | ␊ |
| 18 | #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}␊ |
| 19 | #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);␊ |
| 20 | #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);␊ |
| 21 | #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);␊ |
| 22 | #define DO16(buf) DO8(buf,0); DO8(buf,8);␊ |
| 23 | ␊ |
| 24 | /* use NO_DIVIDE if your processor does not do division in hardware */␊ |
| 25 | #ifdef NO_DIVIDE␊ |
| 26 | # define MOD(a) \␊ |
| 27 | do { \␊ |
| 28 | if (a >= (BASE << 16)) a -= (BASE << 16); \␊ |
| 29 | if (a >= (BASE << 15)) a -= (BASE << 15); \␊ |
| 30 | if (a >= (BASE << 14)) a -= (BASE << 14); \␊ |
| 31 | if (a >= (BASE << 13)) a -= (BASE << 13); \␊ |
| 32 | if (a >= (BASE << 12)) a -= (BASE << 12); \␊ |
| 33 | if (a >= (BASE << 11)) a -= (BASE << 11); \␊ |
| 34 | if (a >= (BASE << 10)) a -= (BASE << 10); \␊ |
| 35 | if (a >= (BASE << 9)) a -= (BASE << 9); \␊ |
| 36 | if (a >= (BASE << 8)) a -= (BASE << 8); \␊ |
| 37 | if (a >= (BASE << 7)) a -= (BASE << 7); \␊ |
| 38 | if (a >= (BASE << 6)) a -= (BASE << 6); \␊ |
| 39 | if (a >= (BASE << 5)) a -= (BASE << 5); \␊ |
| 40 | if (a >= (BASE << 4)) a -= (BASE << 4); \␊ |
| 41 | if (a >= (BASE << 3)) a -= (BASE << 3); \␊ |
| 42 | if (a >= (BASE << 2)) a -= (BASE << 2); \␊ |
| 43 | if (a >= (BASE << 1)) a -= (BASE << 1); \␊ |
| 44 | if (a >= BASE) a -= BASE; \␊ |
| 45 | } while (0)␊ |
| 46 | # define MOD4(a) \␊ |
| 47 | do { \␊ |
| 48 | if (a >= (BASE << 4)) a -= (BASE << 4); \␊ |
| 49 | if (a >= (BASE << 3)) a -= (BASE << 3); \␊ |
| 50 | if (a >= (BASE << 2)) a -= (BASE << 2); \␊ |
| 51 | if (a >= (BASE << 1)) a -= (BASE << 1); \␊ |
| 52 | if (a >= BASE) a -= BASE; \␊ |
| 53 | } while (0)␊ |
| 54 | #else␊ |
| 55 | # define MOD(a) a %= BASE␊ |
| 56 | # define MOD4(a) a %= BASE␊ |
| 57 | #endif␊ |
| 58 | ␊ |
| 59 | /* ========================================================================= */␊ |
| 60 | uLong ZEXPORT adler32(adler, buf, len)␊ |
| 61 | uLong adler;␊ |
| 62 | const Bytef *buf;␊ |
| 63 | uInt len;␊ |
| 64 | {␊ |
| 65 | unsigned long sum2;␊ |
| 66 | unsigned n;␊ |
| 67 | ␊ |
| 68 | /* split Adler-32 into component sums */␊ |
| 69 | sum2 = (adler >> 16) & 0xffff;␊ |
| 70 | adler &= 0xffff;␊ |
| 71 | ␊ |
| 72 | /* in case user likes doing a byte at a time, keep it fast */␊ |
| 73 | if (len == 1) {␊ |
| 74 | adler += buf[0];␊ |
| 75 | if (adler >= BASE)␊ |
| 76 | adler -= BASE;␊ |
| 77 | sum2 += adler;␊ |
| 78 | if (sum2 >= BASE)␊ |
| 79 | sum2 -= BASE;␊ |
| 80 | return adler | (sum2 << 16);␊ |
| 81 | }␊ |
| 82 | ␊ |
| 83 | /* initial Adler-32 value (deferred check for len == 1 speed) */␊ |
| 84 | if (buf == Z_NULL)␊ |
| 85 | return 1L;␊ |
| 86 | ␊ |
| 87 | /* in case short lengths are provided, keep it somewhat fast */␊ |
| 88 | if (len < 16) {␊ |
| 89 | while (len--) {␊ |
| 90 | adler += *buf++;␊ |
| 91 | sum2 += adler;␊ |
| 92 | }␊ |
| 93 | if (adler >= BASE)␊ |
| 94 | adler -= BASE;␊ |
| 95 | MOD4(sum2); /* only added so many BASE's */␊ |
| 96 | return adler | (sum2 << 16);␊ |
| 97 | }␊ |
| 98 | ␊ |
| 99 | /* do length NMAX blocks -- requires just one modulo operation */␊ |
| 100 | while (len >= NMAX) {␊ |
| 101 | len -= NMAX;␊ |
| 102 | n = NMAX / 16; /* NMAX is divisible by 16 */␊ |
| 103 | do {␊ |
| 104 | DO16(buf); /* 16 sums unrolled */␊ |
| 105 | buf += 16;␊ |
| 106 | } while (--n);␊ |
| 107 | MOD(adler);␊ |
| 108 | MOD(sum2);␊ |
| 109 | }␊ |
| 110 | ␊ |
| 111 | /* do remaining bytes (less than NMAX, still just one modulo) */␊ |
| 112 | if (len) { /* avoid modulos if none remaining */␊ |
| 113 | while (len >= 16) {␊ |
| 114 | len -= 16;␊ |
| 115 | DO16(buf);␊ |
| 116 | buf += 16;␊ |
| 117 | }␊ |
| 118 | while (len--) {␊ |
| 119 | adler += *buf++;␊ |
| 120 | sum2 += adler;␊ |
| 121 | }␊ |
| 122 | MOD(adler);␊ |
| 123 | MOD(sum2);␊ |
| 124 | }␊ |
| 125 | ␊ |
| 126 | /* return recombined sums */␊ |
| 127 | return adler | (sum2 << 16);␊ |
| 128 | }␊ |
| 129 | ␊ |
| 130 | /* ========================================================================= */␊ |
| 131 | local uLong adler32_combine_(adler1, adler2, len2)␊ |
| 132 | uLong adler1;␊ |
| 133 | uLong adler2;␊ |
| 134 | z_off64_t len2;␊ |
| 135 | {␊ |
| 136 | unsigned long sum1;␊ |
| 137 | unsigned long sum2;␊ |
| 138 | unsigned rem;␊ |
| 139 | ␊ |
| 140 | /* the derivation of this formula is left as an exercise for the reader */␊ |
| 141 | rem = (unsigned)(len2 % BASE);␊ |
| 142 | sum1 = adler1 & 0xffff;␊ |
| 143 | sum2 = rem * sum1;␊ |
| 144 | MOD(sum2);␊ |
| 145 | sum1 += (adler2 & 0xffff) + BASE - 1;␊ |
| 146 | sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;␊ |
| 147 | if (sum1 >= BASE) sum1 -= BASE;␊ |
| 148 | if (sum1 >= BASE) sum1 -= BASE;␊ |
| 149 | if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1);␊ |
| 150 | if (sum2 >= BASE) sum2 -= BASE;␊ |
| 151 | return sum1 | (sum2 << 16);␊ |
| 152 | }␊ |
| 153 | ␊ |
| 154 | /* ========================================================================= */␊ |
| 155 | uLong ZEXPORT adler32_combine(adler1, adler2, len2)␊ |
| 156 | uLong adler1;␊ |
| 157 | uLong adler2;␊ |
| 158 | z_off_t len2;␊ |
| 159 | {␊ |
| 160 | return adler32_combine_(adler1, adler2, len2);␊ |
| 161 | }␊ |
| 162 | ␊ |
| 163 | uLong ZEXPORT adler32_combine64(adler1, adler2, len2)␊ |
| 164 | uLong adler1;␊ |
| 165 | uLong adler2;␊ |
| 166 | z_off64_t len2;␊ |
| 167 | {␊ |
| 168 | return adler32_combine_(adler1, adler2, len2);␊ |
| 169 | }␊ |
| 170 | |
