1 /* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2011 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_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 13 14 #define BASE 65521 /* 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 try it both ways to see which is faster */ 26 #ifdef NO_DIVIDE 27 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 28 (thank you to John Reiser for pointing this out) */ 29 # define CHOP(a) \ 30 do { \ 31 unsigned long tmp = a >> 16; \ 32 a &= 0xffffUL; \ 33 a += (tmp << 4) - tmp; \ 34 } while (0) 35 # define MOD28(a) \ 36 do { \ 37 CHOP(a); \ 38 if (a >= BASE) a -= BASE; \ 39 } while (0) 40 # define MOD(a) \ 41 do { \ 42 CHOP(a); \ 43 MOD28(a); \ 44 } while (0) 45 # define MOD63(a) \ 46 do { /* this assumes a is not negative */ \ 47 z_off64_t tmp = a >> 32; \ 48 a &= 0xffffffffL; \ 49 a += (tmp << 8) - (tmp << 5) + tmp; \ 50 tmp = a >> 16; \ 51 a &= 0xffffL; \ 52 a += (tmp << 4) - tmp; \ 53 tmp = a >> 16; \ 54 a &= 0xffffL; \ 55 a += (tmp << 4) - tmp; \ 56 if (a >= BASE) a -= BASE; \ 57 } while (0) 58 #else 59 # define MOD(a) a %= BASE 60 # define MOD28(a) a %= BASE 61 # define MOD63(a) a %= BASE 62 #endif 63 64 /* ========================================================================= */ 65 uLong ZEXPORT adler32(adler, buf, len) 66 uLong adler; 67 const Bytef *buf; 68 uInt len; 69 { 70 unsigned long sum2; 71 unsigned n; 72 73 /* split Adler-32 into component sums */ 74 sum2 = (adler >> 16) & 0xffff; 75 adler &= 0xffff; 76 77 /* in case user likes doing a byte at a time, keep it fast */ 78 if (len == 1) { 79 adler += buf[0]; 80 if (adler >= BASE) 81 adler -= BASE; 82 sum2 += adler; 83 if (sum2 >= BASE) 84 sum2 -= BASE; 85 return adler | (sum2 << 16); 86 } 87 88 /* initial Adler-32 value (deferred check for len == 1 speed) */ 89 if (buf == Z_NULL) 90 return 1L; 91 92 /* in case short lengths are provided, keep it somewhat fast */ 93 if (len < 16) { 94 while (len--) { 95 adler += *buf++; 96 sum2 += adler; 97 } 98 if (adler >= BASE) 99 adler -= BASE; 100 MOD28(sum2); /* only added so many BASE's */ 101 return adler | (sum2 << 16); 102 } 103 104 /* do length NMAX blocks -- requires just one modulo operation */ 105 while (len >= NMAX) { 106 len -= NMAX; 107 n = NMAX / 16; /* NMAX is divisible by 16 */ 108 do { 109 DO16(buf); /* 16 sums unrolled */ 110 buf += 16; 111 } while (--n); 112 MOD(adler); 113 MOD(sum2); 114 } 115 116 /* do remaining bytes (less than NMAX, still just one modulo) */ 117 if (len) { /* avoid modulos if none remaining */ 118 while (len >= 16) { 119 len -= 16; 120 DO16(buf); 121 buf += 16; 122 } 123 while (len--) { 124 adler += *buf++; 125 sum2 += adler; 126 } 127 MOD(adler); 128 MOD(sum2); 129 } 130 131 /* return recombined sums */ 132 return adler | (sum2 << 16); 133 } 134 135 /* ========================================================================= */ 136 local uLong adler32_combine_(adler1, adler2, len2) 137 uLong adler1; 138 uLong adler2; 139 z_off64_t len2; 140 { 141 unsigned long sum1; 142 unsigned long sum2; 143 unsigned rem; 144 145 /* for negative len, return invalid adler32 as a clue for debugging */ 146 if (len2 < 0) 147 return 0xffffffffUL; 148 149 /* the derivation of this formula is left as an exercise for the reader */ 150 MOD63(len2); /* assumes len2 >= 0 */ 151 rem = (unsigned)len2; 152 sum1 = adler1 & 0xffff; 153 sum2 = rem * sum1; 154 MOD(sum2); 155 sum1 += (adler2 & 0xffff) + BASE - 1; 156 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 157 if (sum1 >= BASE) sum1 -= BASE; 158 if (sum1 >= BASE) sum1 -= BASE; 159 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1); 160 if (sum2 >= BASE) sum2 -= BASE; 161 return sum1 | (sum2 << 16); 162 } 163 164 /* ========================================================================= */ 165 uLong ZEXPORT adler32_combine(adler1, adler2, len2) 166 uLong adler1; 167 uLong adler2; 168 z_off_t len2; 169 { 170 return adler32_combine_(adler1, adler2, len2); 171 } 172 173 uLong ZEXPORT adler32_combine64(adler1, adler2, len2) 174 uLong adler1; 175 uLong adler2; 176 z_off64_t len2; 177 { 178 return adler32_combine_(adler1, adler2, len2); 179 } 180
