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annotate libs/zlib/adler32.c @ 13:ea928c313344

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author John Tsiombikas <nuclear@member.fsf.org>
date Mon, 28 Sep 2015 19:04:50 +0300
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nuclear@2 1 /* adler32.c -- compute the Adler-32 checksum of a data stream
nuclear@2 2 * Copyright (C) 1995-2004 Mark Adler
nuclear@2 3 * For conditions of distribution and use, see copyright notice in zlib.h
nuclear@2 4 */
nuclear@2 5
nuclear@2 6 /* @(#) $Id$ */
nuclear@2 7
nuclear@2 8 #define ZLIB_INTERNAL
nuclear@2 9 #include "zlib.h"
nuclear@2 10
nuclear@2 11 #define BASE 65521UL /* largest prime smaller than 65536 */
nuclear@2 12 #define NMAX 5552
nuclear@2 13 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
nuclear@2 14
nuclear@2 15 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;}
nuclear@2 16 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
nuclear@2 17 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
nuclear@2 18 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
nuclear@2 19 #define DO16(buf) DO8(buf,0); DO8(buf,8);
nuclear@2 20
nuclear@2 21 /* use NO_DIVIDE if your processor does not do division in hardware */
nuclear@2 22 #ifdef NO_DIVIDE
nuclear@2 23 # define MOD(a) \
nuclear@2 24 do { \
nuclear@2 25 if (a >= (BASE << 16)) a -= (BASE << 16); \
nuclear@2 26 if (a >= (BASE << 15)) a -= (BASE << 15); \
nuclear@2 27 if (a >= (BASE << 14)) a -= (BASE << 14); \
nuclear@2 28 if (a >= (BASE << 13)) a -= (BASE << 13); \
nuclear@2 29 if (a >= (BASE << 12)) a -= (BASE << 12); \
nuclear@2 30 if (a >= (BASE << 11)) a -= (BASE << 11); \
nuclear@2 31 if (a >= (BASE << 10)) a -= (BASE << 10); \
nuclear@2 32 if (a >= (BASE << 9)) a -= (BASE << 9); \
nuclear@2 33 if (a >= (BASE << 8)) a -= (BASE << 8); \
nuclear@2 34 if (a >= (BASE << 7)) a -= (BASE << 7); \
nuclear@2 35 if (a >= (BASE << 6)) a -= (BASE << 6); \
nuclear@2 36 if (a >= (BASE << 5)) a -= (BASE << 5); \
nuclear@2 37 if (a >= (BASE << 4)) a -= (BASE << 4); \
nuclear@2 38 if (a >= (BASE << 3)) a -= (BASE << 3); \
nuclear@2 39 if (a >= (BASE << 2)) a -= (BASE << 2); \
nuclear@2 40 if (a >= (BASE << 1)) a -= (BASE << 1); \
nuclear@2 41 if (a >= BASE) a -= BASE; \
nuclear@2 42 } while (0)
nuclear@2 43 # define MOD4(a) \
nuclear@2 44 do { \
nuclear@2 45 if (a >= (BASE << 4)) a -= (BASE << 4); \
nuclear@2 46 if (a >= (BASE << 3)) a -= (BASE << 3); \
nuclear@2 47 if (a >= (BASE << 2)) a -= (BASE << 2); \
nuclear@2 48 if (a >= (BASE << 1)) a -= (BASE << 1); \
nuclear@2 49 if (a >= BASE) a -= BASE; \
nuclear@2 50 } while (0)
nuclear@2 51 #else
nuclear@2 52 # define MOD(a) a %= BASE
nuclear@2 53 # define MOD4(a) a %= BASE
nuclear@2 54 #endif
nuclear@2 55
nuclear@2 56 /* ========================================================================= */
nuclear@2 57 uLong ZEXPORT adler32(adler, buf, len)
nuclear@2 58 uLong adler;
nuclear@2 59 const Bytef *buf;
nuclear@2 60 uInt len;
nuclear@2 61 {
nuclear@2 62 unsigned long sum2;
nuclear@2 63 unsigned n;
nuclear@2 64
nuclear@2 65 /* split Adler-32 into component sums */
nuclear@2 66 sum2 = (adler >> 16) & 0xffff;
nuclear@2 67 adler &= 0xffff;
nuclear@2 68
nuclear@2 69 /* in case user likes doing a byte at a time, keep it fast */
nuclear@2 70 if (len == 1) {
nuclear@2 71 adler += buf[0];
nuclear@2 72 if (adler >= BASE)
nuclear@2 73 adler -= BASE;
nuclear@2 74 sum2 += adler;
nuclear@2 75 if (sum2 >= BASE)
nuclear@2 76 sum2 -= BASE;
nuclear@2 77 return adler | (sum2 << 16);
nuclear@2 78 }
nuclear@2 79
nuclear@2 80 /* initial Adler-32 value (deferred check for len == 1 speed) */
nuclear@2 81 if (buf == Z_NULL)
nuclear@2 82 return 1L;
nuclear@2 83
nuclear@2 84 /* in case short lengths are provided, keep it somewhat fast */
nuclear@2 85 if (len < 16) {
nuclear@2 86 while (len--) {
nuclear@2 87 adler += *buf++;
nuclear@2 88 sum2 += adler;
nuclear@2 89 }
nuclear@2 90 if (adler >= BASE)
nuclear@2 91 adler -= BASE;
nuclear@2 92 MOD4(sum2); /* only added so many BASE's */
nuclear@2 93 return adler | (sum2 << 16);
nuclear@2 94 }
nuclear@2 95
nuclear@2 96 /* do length NMAX blocks -- requires just one modulo operation */
nuclear@2 97 while (len >= NMAX) {
nuclear@2 98 len -= NMAX;
nuclear@2 99 n = NMAX / 16; /* NMAX is divisible by 16 */
nuclear@2 100 do {
nuclear@2 101 DO16(buf); /* 16 sums unrolled */
nuclear@2 102 buf += 16;
nuclear@2 103 } while (--n);
nuclear@2 104 MOD(adler);
nuclear@2 105 MOD(sum2);
nuclear@2 106 }
nuclear@2 107
nuclear@2 108 /* do remaining bytes (less than NMAX, still just one modulo) */
nuclear@2 109 if (len) { /* avoid modulos if none remaining */
nuclear@2 110 while (len >= 16) {
nuclear@2 111 len -= 16;
nuclear@2 112 DO16(buf);
nuclear@2 113 buf += 16;
nuclear@2 114 }
nuclear@2 115 while (len--) {
nuclear@2 116 adler += *buf++;
nuclear@2 117 sum2 += adler;
nuclear@2 118 }
nuclear@2 119 MOD(adler);
nuclear@2 120 MOD(sum2);
nuclear@2 121 }
nuclear@2 122
nuclear@2 123 /* return recombined sums */
nuclear@2 124 return adler | (sum2 << 16);
nuclear@2 125 }
nuclear@2 126
nuclear@2 127 /* ========================================================================= */
nuclear@2 128 uLong ZEXPORT adler32_combine(adler1, adler2, len2)
nuclear@2 129 uLong adler1;
nuclear@2 130 uLong adler2;
nuclear@2 131 z_off_t len2;
nuclear@2 132 {
nuclear@2 133 unsigned long sum1;
nuclear@2 134 unsigned long sum2;
nuclear@2 135 unsigned rem;
nuclear@2 136
nuclear@2 137 /* the derivation of this formula is left as an exercise for the reader */
nuclear@2 138 rem = (unsigned)(len2 % BASE);
nuclear@2 139 sum1 = adler1 & 0xffff;
nuclear@2 140 sum2 = rem * sum1;
nuclear@2 141 MOD(sum2);
nuclear@2 142 sum1 += (adler2 & 0xffff) + BASE - 1;
nuclear@2 143 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
nuclear@2 144 if (sum1 > BASE) sum1 -= BASE;
nuclear@2 145 if (sum1 > BASE) sum1 -= BASE;
nuclear@2 146 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
nuclear@2 147 if (sum2 > BASE) sum2 -= BASE;
nuclear@2 148 return sum1 | (sum2 << 16);
nuclear@2 149 }