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
