1/* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2004 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 */ 5 6/* @(#) $Id: adler32.c,v 1.1.1.1 2011/06/10 09:34:40 andrew Exp $ */ 7 8#include "zutil.h" 9 10#define BASE 65521UL /* 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#ifdef NO_DIVIDE 22# define MOD(a) \ 23 do { \ 24 if (a >= (BASE << 16)) a -= (BASE << 16); \ 25 if (a >= (BASE << 15)) a -= (BASE << 15); \ 26 if (a >= (BASE << 14)) a -= (BASE << 14); \ 27 if (a >= (BASE << 13)) a -= (BASE << 13); \ 28 if (a >= (BASE << 12)) a -= (BASE << 12); \ 29 if (a >= (BASE << 11)) a -= (BASE << 11); \ 30 if (a >= (BASE << 10)) a -= (BASE << 10); \ 31 if (a >= (BASE << 9)) a -= (BASE << 9); \ 32 if (a >= (BASE << 8)) a -= (BASE << 8); \ 33 if (a >= (BASE << 7)) a -= (BASE << 7); \ 34 if (a >= (BASE << 6)) a -= (BASE << 6); \ 35 if (a >= (BASE << 5)) a -= (BASE << 5); \ 36 if (a >= (BASE << 4)) a -= (BASE << 4); \ 37 if (a >= (BASE << 3)) a -= (BASE << 3); \ 38 if (a >= (BASE << 2)) a -= (BASE << 2); \ 39 if (a >= (BASE << 1)) a -= (BASE << 1); \ 40 if (a >= BASE) a -= BASE; \ 41 } while (0) 42# define MOD4(a) \ 43 do { \ 44 if (a >= (BASE << 4)) a -= (BASE << 4); \ 45 if (a >= (BASE << 3)) a -= (BASE << 3); \ 46 if (a >= (BASE << 2)) a -= (BASE << 2); \ 47 if (a >= (BASE << 1)) a -= (BASE << 1); \ 48 if (a >= BASE) a -= BASE; \ 49 } while (0) 50#else 51# define MOD(a) a %= BASE 52# define MOD4(a) a %= BASE 53#endif 54 55/* ========================================================================= */ 56uLong ZEXPORT adler32(adler, buf, len) 57 uLong adler; 58 const Bytef *buf; 59 uInt len; 60{ 61 unsigned long sum2; 62 unsigned n; 63 64 /* split Adler-32 into component sums */ 65 sum2 = (adler >> 16) & 0xffff; 66 adler &= 0xffff; 67 68 /* in case user likes doing a byte at a time, keep it fast */ 69 if (len == 1) { 70 adler += buf[0]; 71 if (adler >= BASE) 72 adler -= BASE; 73 sum2 += adler; 74 if (sum2 >= BASE) 75 sum2 -= BASE; 76 return adler | (sum2 << 16); 77 } 78 79 /* initial Adler-32 value (deferred check for len == 1 speed) */ 80 if (buf == Z_NULL) 81 return 1L; 82 83 /* in case short lengths are provided, keep it somewhat fast */ 84 if (len < 16) { 85 while (len--) { 86 adler += *buf++; 87 sum2 += adler; 88 } 89 if (adler >= BASE) 90 adler -= BASE; 91 MOD4(sum2); /* only added so many BASE's */ 92 return adler | (sum2 << 16); 93 } 94 95 /* do length NMAX blocks -- requires just one modulo operation */ 96 while (len >= NMAX) { 97 len -= NMAX; 98 n = NMAX / 16; /* NMAX is divisible by 16 */ 99 do { 100 DO16(buf); /* 16 sums unrolled */ 101 buf += 16; 102 } while (--n); 103 MOD(adler); 104 MOD(sum2); 105 } 106 107 /* do remaining bytes (less than NMAX, still just one modulo) */ 108 if (len) { /* avoid modulos if none remaining */ 109 while (len >= 16) { 110 len -= 16; 111 DO16(buf); 112 buf += 16; 113 } 114 while (len--) { 115 adler += *buf++; 116 sum2 += adler; 117 } 118 MOD(adler); 119 MOD(sum2); 120 } 121 122 /* return recombined sums */ 123 return adler | (sum2 << 16); 124} 125 126/* ========================================================================= */ 127uLong ZEXPORT adler32_combine(adler1, adler2, len2) 128 uLong adler1; 129 uLong adler2; 130 z_off_t len2; 131{ 132 unsigned long sum1; 133 unsigned long sum2; 134 unsigned rem; 135 136 /* the derivation of this formula is left as an exercise for the reader */ 137 rem = (unsigned)(len2 % BASE); 138 sum1 = adler1 & 0xffff; 139 sum2 = rem * sum1; 140 MOD(sum2); 141 sum1 += (adler2 & 0xffff) + BASE - 1; 142 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 143 if (sum1 > BASE) sum1 -= BASE; 144 if (sum1 > BASE) sum1 -= BASE; 145 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1); 146 if (sum2 > BASE) sum2 -= BASE; 147 return sum1 | (sum2 << 16); 148} 149