1 /* $NetBSD: adler32.c,v 1.1.1.1 2006/01/14 20:10:24 christos Exp $ */ 2 3 /* adler32.c -- compute the Adler-32 checksum of a data stream 4 * Copyright (C) 1995-2004 Mark Adler 5 * For conditions of distribution and use, see copyright notice in zlib.h 6 */ 7 8 /* @(#) Id */ 9 10 #define ZLIB_INTERNAL 11 #include "zlib.h" 12 13 #define BASE 65521UL /* largest prime smaller than 65536 */ 14 #define NMAX 5552 15 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 16 17 #define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 18 #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 19 #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 20 #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 21 #define DO16(buf) DO8(buf,0); DO8(buf,8); 22 23 /* use NO_DIVIDE if your processor does not do division in hardware */ 24 #ifdef NO_DIVIDE 25 # define MOD(a) \ 26 do { \ 27 if (a >= (BASE << 16)) a -= (BASE << 16); \ 28 if (a >= (BASE << 15)) a -= (BASE << 15); \ 29 if (a >= (BASE << 14)) a -= (BASE << 14); \ 30 if (a >= (BASE << 13)) a -= (BASE << 13); \ 31 if (a >= (BASE << 12)) a -= (BASE << 12); \ 32 if (a >= (BASE << 11)) a -= (BASE << 11); \ 33 if (a >= (BASE << 10)) a -= (BASE << 10); \ 34 if (a >= (BASE << 9)) a -= (BASE << 9); \ 35 if (a >= (BASE << 8)) a -= (BASE << 8); \ 36 if (a >= (BASE << 7)) a -= (BASE << 7); \ 37 if (a >= (BASE << 6)) a -= (BASE << 6); \ 38 if (a >= (BASE << 5)) a -= (BASE << 5); \ 39 if (a >= (BASE << 4)) a -= (BASE << 4); \ 40 if (a >= (BASE << 3)) a -= (BASE << 3); \ 41 if (a >= (BASE << 2)) a -= (BASE << 2); \ 42 if (a >= (BASE << 1)) a -= (BASE << 1); \ 43 if (a >= BASE) a -= BASE; \ 44 } while (0) 45 # define MOD4(a) \ 46 do { \ 47 if (a >= (BASE << 4)) a -= (BASE << 4); \ 48 if (a >= (BASE << 3)) a -= (BASE << 3); \ 49 if (a >= (BASE << 2)) a -= (BASE << 2); \ 50 if (a >= (BASE << 1)) a -= (BASE << 1); \ 51 if (a >= BASE) a -= BASE; \ 52 } while (0) 53 #else 54 # define MOD(a) a %= BASE 55 # define MOD4(a) a %= BASE 56 #endif 57 58 /* ========================================================================= */ 59 uLong ZEXPORT adler32(adler, buf, len) 60 uLong adler; 61 const Bytef *buf; 62 uInt len; 63 { 64 unsigned long sum2; 65 unsigned n; 66 67 /* split Adler-32 into component sums */ 68 sum2 = (adler >> 16) & 0xffff; 69 adler &= 0xffff; 70 71 /* in case user likes doing a byte at a time, keep it fast */ 72 if (len == 1) { 73 adler += buf[0]; 74 if (adler >= BASE) 75 adler -= BASE; 76 sum2 += adler; 77 if (sum2 >= BASE) 78 sum2 -= BASE; 79 return adler | (sum2 << 16); 80 } 81 82 /* initial Adler-32 value (deferred check for len == 1 speed) */ 83 if (buf == Z_NULL) 84 return 1L; 85 86 /* in case short lengths are provided, keep it somewhat fast */ 87 if (len < 16) { 88 while (len--) { 89 adler += *buf++; 90 sum2 += adler; 91 } 92 if (adler >= BASE) 93 adler -= BASE; 94 MOD4(sum2); /* only added so many BASE's */ 95 return adler | (sum2 << 16); 96 } 97 98 /* do length NMAX blocks -- requires just one modulo operation */ 99 while (len >= NMAX) { 100 len -= NMAX; 101 n = NMAX / 16; /* NMAX is divisible by 16 */ 102 do { 103 DO16(buf); /* 16 sums unrolled */ 104 buf += 16; 105 } while (--n); 106 MOD(adler); 107 MOD(sum2); 108 } 109 110 /* do remaining bytes (less than NMAX, still just one modulo) */ 111 if (len) { /* avoid modulos if none remaining */ 112 while (len >= 16) { 113 len -= 16; 114 DO16(buf); 115 buf += 16; 116 } 117 while (len--) { 118 adler += *buf++; 119 sum2 += adler; 120 } 121 MOD(adler); 122 MOD(sum2); 123 } 124 125 /* return recombined sums */ 126 return adler | (sum2 << 16); 127 } 128 129 /* ========================================================================= */ 130 uLong ZEXPORT adler32_combine(adler1, adler2, len2) 131 uLong adler1; 132 uLong adler2; 133 z_off_t len2; 134 { 135 unsigned long sum1; 136 unsigned long sum2; 137 unsigned rem; 138 139 /* the derivation of this formula is left as an exercise for the reader */ 140 rem = (unsigned)(len2 % BASE); 141 sum1 = adler1 & 0xffff; 142 sum2 = rem * sum1; 143 MOD(sum2); 144 sum1 += (adler2 & 0xffff) + BASE - 1; 145 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 146 if (sum1 > BASE) sum1 -= BASE; 147 if (sum1 > BASE) sum1 -= BASE; 148 if (sum2 > (BASE << 1)) sum2 -= (BASE << 1); 149 if (sum2 > BASE) sum2 -= BASE; 150 return sum1 | (sum2 << 16); 151 } 152