adler32.c (4964B)
1 /* adler32.c -- compute the Adler-32 checksum of a data stream 2 * Copyright (C) 1995-2011, 2016 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 BASE 65521U /* 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 try it both ways to see which is faster */ 22 #ifdef NO_DIVIDE 23 /* note that this assumes BASE is 65521, where 65536 % 65521 == 15 24 (thank you to John Reiser for pointing this out) */ 25 # define CHOP(a) \ 26 do { \ 27 unsigned long tmp = a >> 16; \ 28 a &= 0xffffUL; \ 29 a += (tmp << 4) - tmp; \ 30 } while (0) 31 # define MOD28(a) \ 32 do { \ 33 CHOP(a); \ 34 if (a >= BASE) a -= BASE; \ 35 } while (0) 36 # define MOD(a) \ 37 do { \ 38 CHOP(a); \ 39 MOD28(a); \ 40 } while (0) 41 # define MOD63(a) \ 42 do { /* this assumes a is not negative */ \ 43 z_off64_t tmp = a >> 32; \ 44 a &= 0xffffffffL; \ 45 a += (tmp << 8) - (tmp << 5) + tmp; \ 46 tmp = a >> 16; \ 47 a &= 0xffffL; \ 48 a += (tmp << 4) - tmp; \ 49 tmp = a >> 16; \ 50 a &= 0xffffL; \ 51 a += (tmp << 4) - tmp; \ 52 if (a >= BASE) a -= BASE; \ 53 } while (0) 54 #else 55 # define MOD(a) a %= BASE 56 # define MOD28(a) a %= BASE 57 # define MOD63(a) a %= BASE 58 #endif 59 60 /* ========================================================================= */ 61 uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len) { 62 unsigned long sum2; 63 unsigned n; 64 65 /* split Adler-32 into component sums */ 66 sum2 = (adler >> 16) & 0xffff; 67 adler &= 0xffff; 68 69 /* in case user likes doing a byte at a time, keep it fast */ 70 if (len == 1) { 71 adler += buf[0]; 72 if (adler >= BASE) 73 adler -= BASE; 74 sum2 += adler; 75 if (sum2 >= BASE) 76 sum2 -= BASE; 77 return adler | (sum2 << 16); 78 } 79 80 /* initial Adler-32 value (deferred check for len == 1 speed) */ 81 if (buf == Z_NULL) 82 return 1L; 83 84 /* in case short lengths are provided, keep it somewhat fast */ 85 if (len < 16) { 86 while (len--) { 87 adler += *buf++; 88 sum2 += adler; 89 } 90 if (adler >= BASE) 91 adler -= BASE; 92 MOD28(sum2); /* only added so many BASE's */ 93 return adler | (sum2 << 16); 94 } 95 96 /* do length NMAX blocks -- requires just one modulo operation */ 97 while (len >= NMAX) { 98 len -= NMAX; 99 n = NMAX / 16; /* NMAX is divisible by 16 */ 100 do { 101 DO16(buf); /* 16 sums unrolled */ 102 buf += 16; 103 } while (--n); 104 MOD(adler); 105 MOD(sum2); 106 } 107 108 /* do remaining bytes (less than NMAX, still just one modulo) */ 109 if (len) { /* avoid modulos if none remaining */ 110 while (len >= 16) { 111 len -= 16; 112 DO16(buf); 113 buf += 16; 114 } 115 while (len--) { 116 adler += *buf++; 117 sum2 += adler; 118 } 119 MOD(adler); 120 MOD(sum2); 121 } 122 123 /* return recombined sums */ 124 return adler | (sum2 << 16); 125 } 126 127 /* ========================================================================= */ 128 uLong ZEXPORT adler32(uLong adler, const Bytef *buf, uInt len) { 129 return adler32_z(adler, buf, len); 130 } 131 132 /* ========================================================================= */ 133 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2) { 134 unsigned long sum1; 135 unsigned long sum2; 136 unsigned rem; 137 138 /* for negative len, return invalid adler32 as a clue for debugging */ 139 if (len2 < 0) 140 return 0xffffffffUL; 141 142 /* the derivation of this formula is left as an exercise for the reader */ 143 MOD63(len2); /* assumes len2 >= 0 */ 144 rem = (unsigned)len2; 145 sum1 = adler1 & 0xffff; 146 sum2 = rem * sum1; 147 MOD(sum2); 148 sum1 += (adler2 & 0xffff) + BASE - 1; 149 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 150 if (sum1 >= BASE) sum1 -= BASE; 151 if (sum1 >= BASE) sum1 -= BASE; 152 if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); 153 if (sum2 >= BASE) sum2 -= BASE; 154 return sum1 | (sum2 << 16); 155 } 156 157 /* ========================================================================= */ 158 uLong ZEXPORT adler32_combine(uLong adler1, uLong adler2, z_off_t len2) { 159 return adler32_combine_(adler1, adler2, len2); 160 } 161 162 uLong ZEXPORT adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) { 163 return adler32_combine_(adler1, adler2, len2); 164 }