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#include <lib/cksum.h> 11 12#define BASE 65521 /* largest prime smaller than 65536 */ 13#define NMAX 5552 14/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 15 16#define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 17#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 18#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 19#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 20#define DO16(buf) DO8(buf,0); DO8(buf,8); 21 22/* use NO_DIVIDE if your processor does not do division in hardware -- 23 try it both ways to see which is faster */ 24#ifdef NO_DIVIDE 25/* note that this assumes BASE is 65521, where 65536 % 65521 == 15 26 (thank you to John Reiser for pointing this out) */ 27# define CHOP(a) \ 28 do { \ 29 uint32_t tmp = a >> 16; \ 30 a &= 0xffffUL; \ 31 a += (tmp << 4) - tmp; \ 32 } while (0) 33# define MOD28(a) \ 34 do { \ 35 CHOP(a); \ 36 if (a >= BASE) a -= BASE; \ 37 } while (0) 38# define MOD(a) \ 39 do { \ 40 CHOP(a); \ 41 MOD28(a); \ 42 } while (0) 43# define MOD63(a) \ 44 do { /* this assumes a is not negative */ \ 45 z_off64_t tmp = a >> 32; \ 46 a &= 0xffffffffL; \ 47 a += (tmp << 8) - (tmp << 5) + tmp; \ 48 tmp = a >> 16; \ 49 a &= 0xffffL; \ 50 a += (tmp << 4) - tmp; \ 51 tmp = a >> 16; \ 52 a &= 0xffffL; \ 53 a += (tmp << 4) - tmp; \ 54 if (a >= BASE) a -= BASE; \ 55 } while (0) 56#else 57# define MOD(a) a %= BASE 58# define MOD28(a) a %= BASE 59# define MOD63(a) a %= BASE 60#endif 61 62/* ========================================================================= */ 63uint32_t ZEXPORT adler32(uint32_t adler, const uint8_t* buf, size_t len) 64{ 65 uint32_t sum2; 66 uint32_t 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 MOD28(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/* ========================================================================= */ 131uint32_t ZEXPORT adler32_combine(uint32_t adler1, uint32_t adler2, size_t len2) 132{ 133 uint32_t sum1; 134 uint32_t sum2; 135 uint32_t rem; 136 137 /* the derivation of this formula is left as an exercise for the reader */ 138 MOD63(len2); /* assumes len2 >= 0 */ 139 rem = (uint32_t)len2; 140 sum1 = adler1 & 0xffff; 141 sum2 = rem * sum1; 142 MOD(sum2); 143 sum1 += (adler2 & 0xffff) + BASE - 1; 144 sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 145 if (sum1 >= BASE) sum1 -= BASE; 146 if (sum1 >= BASE) sum1 -= BASE; 147 if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1); 148 if (sum2 >= BASE) sum2 -= BASE; 149 return sum1 | (sum2 << 16); 150} 151