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 "hammer2_zlib_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 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 local uLong adler32_combine_(uLong adler1, uLong adler2, z_off64_t len2); 65 uLong adler32_combine(uLong adler1, uLong adler2, z_off_t len2); 66 67 /* ========================================================================= */ 68 uLong 69 adler32(uLong adler, const Bytef *buf, uInt len) 70 { 71 unsigned long sum2; 72 unsigned n; 73 74 /* split Adler-32 into component sums */ 75 sum2 = (adler >> 16) & 0xffff; 76 adler &= 0xffff; 77 78 /* in case user likes doing a byte at a time, keep it fast */ 79 if (len == 1) { 80 adler += buf[0]; 81 if (adler >= BASE) 82 adler -= BASE; 83 sum2 += adler; 84 if (sum2 >= BASE) 85 sum2 -= BASE; 86 return adler | (sum2 << 16); 87 } 88 89 /* initial Adler-32 value (deferred check for len == 1 speed) */ 90 if (buf == Z_NULL) 91 return 1L; 92 93 /* in case short lengths are provided, keep it somewhat fast */ 94 if (len < 16) { 95 while (len--) { 96 adler += *buf++; 97 sum2 += adler; 98 } 99 if (adler >= BASE) 100 adler -= BASE; 101 MOD28(sum2); /* only added so many BASE's */ 102 return adler | (sum2 << 16); 103 } 104 105 /* do length NMAX blocks -- requires just one modulo operation */ 106 while (len >= NMAX) { 107 len -= NMAX; 108 n = NMAX / 16; /* NMAX is divisible by 16 */ 109 do { 110 DO16(buf); /* 16 sums unrolled */ 111 buf += 16; 112 } while (--n); 113 MOD(adler); 114 MOD(sum2); 115 } 116 117 /* do remaining bytes (less than NMAX, still just one modulo) */ 118 if (len) { /* avoid modulos if none remaining */ 119 while (len >= 16) { 120 len -= 16; 121 DO16(buf); 122 buf += 16; 123 } 124 while (len--) { 125 adler += *buf++; 126 sum2 += adler; 127 } 128 MOD(adler); 129 MOD(sum2); 130 } 131 132 /* return recombined sums */ 133 return adler | (sum2 << 16); 134 } 135 136 /* ========================================================================= */ 137 local 138 uLong 139 adler32_combine_(uLong adler1, uLong adler2, 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 166 adler32_combine(uLong adler1, uLong adler2, z_off_t len2) 167 { 168 return adler32_combine_(adler1, adler2, len2); 169 } 170 171 uLong 172 adler32_combine64(uLong adler1, uLong adler2, z_off64_t len2) 173 { 174 return adler32_combine_(adler1, adler2, len2); 175 } 176