117651Speter/* adler32.c -- compute the Adler-32 checksum of a data stream 2237410Sdelphij * Copyright (C) 1995-2011 Mark Adler 3131380Stjr * For conditions of distribution and use, see copyright notice in zlib.h 417651Speter */ 517651Speter 6146081Skientzle/* @(#) $Id$ */ 717651Speter 8205471Sdelphij#include "zutil.h" 917651Speter 10205471Sdelphij#define local static 11205471Sdelphij 12237410Sdelphijlocal uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 13205471Sdelphij 14237410Sdelphij#define BASE 65521 /* largest prime smaller than 65536 */ 1517651Speter#define NMAX 5552 1617651Speter/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 1717651Speter 18157046Sdes#define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 1917651Speter#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 2017651Speter#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 2117651Speter#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 2217651Speter#define DO16(buf) DO8(buf,0); DO8(buf,8); 2317651Speter 24237410Sdelphij/* use NO_DIVIDE if your processor does not do division in hardware -- 25237410Sdelphij try it both ways to see which is faster */ 26131380Stjr#ifdef NO_DIVIDE 27237410Sdelphij/* note that this assumes BASE is 65521, where 65536 % 65521 == 15 28237410Sdelphij (thank you to John Reiser for pointing this out) */ 29237410Sdelphij# define CHOP(a) \ 30131380Stjr do { \ 31237410Sdelphij unsigned long tmp = a >> 16; \ 32237410Sdelphij a &= 0xffffUL; \ 33237410Sdelphij a += (tmp << 4) - tmp; \ 34237410Sdelphij } while (0) 35237410Sdelphij# define MOD28(a) \ 36237410Sdelphij do { \ 37237410Sdelphij CHOP(a); \ 38131380Stjr if (a >= BASE) a -= BASE; \ 39131380Stjr } while (0) 40237410Sdelphij# define MOD(a) \ 41157046Sdes do { \ 42237410Sdelphij CHOP(a); \ 43237410Sdelphij MOD28(a); \ 44237410Sdelphij } while (0) 45237410Sdelphij# define MOD63(a) \ 46237410Sdelphij do { /* this assumes a is not negative */ \ 47237410Sdelphij z_off64_t tmp = a >> 32; \ 48237410Sdelphij a &= 0xffffffffL; \ 49237410Sdelphij a += (tmp << 8) - (tmp << 5) + tmp; \ 50237410Sdelphij tmp = a >> 16; \ 51237410Sdelphij a &= 0xffffL; \ 52237410Sdelphij a += (tmp << 4) - tmp; \ 53237410Sdelphij tmp = a >> 16; \ 54237410Sdelphij a &= 0xffffL; \ 55237410Sdelphij a += (tmp << 4) - tmp; \ 56157046Sdes if (a >= BASE) a -= BASE; \ 57157046Sdes } while (0) 58131380Stjr#else 59131380Stjr# define MOD(a) a %= BASE 60237410Sdelphij# define MOD28(a) a %= BASE 61237410Sdelphij# define MOD63(a) a %= BASE 62131380Stjr#endif 63131380Stjr 6417651Speter/* ========================================================================= */ 6533908SsteveuLong ZEXPORT adler32(adler, buf, len) 6617651Speter uLong adler; 6717651Speter const Bytef *buf; 6817651Speter uInt len; 6917651Speter{ 70157046Sdes unsigned long sum2; 71157046Sdes unsigned n; 7217651Speter 73157046Sdes /* split Adler-32 into component sums */ 74157046Sdes sum2 = (adler >> 16) & 0xffff; 75157046Sdes adler &= 0xffff; 7617651Speter 77157046Sdes /* in case user likes doing a byte at a time, keep it fast */ 78157046Sdes if (len == 1) { 79157046Sdes adler += buf[0]; 80157046Sdes if (adler >= BASE) 81157046Sdes adler -= BASE; 82157046Sdes sum2 += adler; 83157046Sdes if (sum2 >= BASE) 84157046Sdes sum2 -= BASE; 85157046Sdes return adler | (sum2 << 16); 86157046Sdes } 87157046Sdes 88157046Sdes /* initial Adler-32 value (deferred check for len == 1 speed) */ 89157046Sdes if (buf == Z_NULL) 90157046Sdes return 1L; 91157046Sdes 92157046Sdes /* in case short lengths are provided, keep it somewhat fast */ 93157046Sdes if (len < 16) { 94157046Sdes while (len--) { 95157046Sdes adler += *buf++; 96157046Sdes sum2 += adler; 97157046Sdes } 98157046Sdes if (adler >= BASE) 99157046Sdes adler -= BASE; 100237410Sdelphij MOD28(sum2); /* only added so many BASE's */ 101157046Sdes return adler | (sum2 << 16); 102157046Sdes } 103157046Sdes 104157046Sdes /* do length NMAX blocks -- requires just one modulo operation */ 105157046Sdes while (len >= NMAX) { 106157046Sdes len -= NMAX; 107157046Sdes n = NMAX / 16; /* NMAX is divisible by 16 */ 108157046Sdes do { 109157046Sdes DO16(buf); /* 16 sums unrolled */ 110157046Sdes buf += 16; 111157046Sdes } while (--n); 112157046Sdes MOD(adler); 113157046Sdes MOD(sum2); 114157046Sdes } 115157046Sdes 116157046Sdes /* do remaining bytes (less than NMAX, still just one modulo) */ 117157046Sdes if (len) { /* avoid modulos if none remaining */ 118157046Sdes while (len >= 16) { 119157046Sdes len -= 16; 12017651Speter DO16(buf); 121131380Stjr buf += 16; 12217651Speter } 123157046Sdes while (len--) { 124157046Sdes adler += *buf++; 125157046Sdes sum2 += adler; 126157046Sdes } 127157046Sdes MOD(adler); 128157046Sdes MOD(sum2); 12917651Speter } 130157046Sdes 131157046Sdes /* return recombined sums */ 132157046Sdes return adler | (sum2 << 16); 13317651Speter} 134157046Sdes 135157046Sdes/* ========================================================================= */ 136205471Sdelphijlocal uLong adler32_combine_(adler1, adler2, len2) 137157046Sdes uLong adler1; 138157046Sdes uLong adler2; 139205471Sdelphij z_off64_t len2; 140157046Sdes{ 141157046Sdes unsigned long sum1; 142157046Sdes unsigned long sum2; 143157046Sdes unsigned rem; 144157046Sdes 145237410Sdelphij /* for negative len, return invalid adler32 as a clue for debugging */ 146237410Sdelphij if (len2 < 0) 147237410Sdelphij return 0xffffffffUL; 148237410Sdelphij 149157046Sdes /* the derivation of this formula is left as an exercise for the reader */ 150237410Sdelphij MOD63(len2); /* assumes len2 >= 0 */ 151237410Sdelphij rem = (unsigned)len2; 152157046Sdes sum1 = adler1 & 0xffff; 153157046Sdes sum2 = rem * sum1; 154157046Sdes MOD(sum2); 155157046Sdes sum1 += (adler2 & 0xffff) + BASE - 1; 156157046Sdes sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 157205471Sdelphij if (sum1 >= BASE) sum1 -= BASE; 158205471Sdelphij if (sum1 >= BASE) sum1 -= BASE; 159205471Sdelphij if (sum2 >= (BASE << 1)) sum2 -= (BASE << 1); 160205471Sdelphij if (sum2 >= BASE) sum2 -= BASE; 161157046Sdes return sum1 | (sum2 << 16); 162157046Sdes} 163205471Sdelphij 164205471Sdelphij/* ========================================================================= */ 165205471SdelphijuLong ZEXPORT adler32_combine(adler1, adler2, len2) 166205471Sdelphij uLong adler1; 167205471Sdelphij uLong adler2; 168205471Sdelphij z_off_t len2; 169205471Sdelphij{ 170205471Sdelphij return adler32_combine_(adler1, adler2, len2); 171205471Sdelphij} 172205471Sdelphij 173205471SdelphijuLong ZEXPORT adler32_combine64(adler1, adler2, len2) 174205471Sdelphij uLong adler1; 175205471Sdelphij uLong adler2; 176205471Sdelphij z_off64_t len2; 177205471Sdelphij{ 178205471Sdelphij return adler32_combine_(adler1, adler2, len2); 179205471Sdelphij} 180