117651Speter/* adler32.c -- compute the Adler-32 checksum of a data stream 2313796Sdelphij * Copyright (C) 1995-2011, 2016 Mark Adler 3131377Stjr * For conditions of distribution and use, see copyright notice in zlib.h 417651Speter */ 517651Speter 633904Ssteve/* @(#) $Id$ */ 717651Speter 8205194Sdelphij#include "zutil.h" 917651Speter 10230837Sdelphijlocal uLong adler32_combine_ OF((uLong adler1, uLong adler2, z_off64_t len2)); 11205194Sdelphij 12313796Sdelphij#define BASE 65521U /* largest prime smaller than 65536 */ 1317651Speter#define NMAX 5552 1417651Speter/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ 1517651Speter 16157043Sdes#define DO1(buf,i) {adler += (buf)[i]; sum2 += adler;} 1717651Speter#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); 1817651Speter#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); 1917651Speter#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); 2017651Speter#define DO16(buf) DO8(buf,0); DO8(buf,8); 2117651Speter 22230837Sdelphij/* use NO_DIVIDE if your processor does not do division in hardware -- 23230837Sdelphij try it both ways to see which is faster */ 24131377Stjr#ifdef NO_DIVIDE 25230837Sdelphij/* note that this assumes BASE is 65521, where 65536 % 65521 == 15 26230837Sdelphij (thank you to John Reiser for pointing this out) */ 27230837Sdelphij# define CHOP(a) \ 28131377Stjr do { \ 29230837Sdelphij unsigned long tmp = a >> 16; \ 30230837Sdelphij a &= 0xffffUL; \ 31230837Sdelphij a += (tmp << 4) - tmp; \ 32230837Sdelphij } while (0) 33230837Sdelphij# define MOD28(a) \ 34230837Sdelphij do { \ 35230837Sdelphij CHOP(a); \ 36131377Stjr if (a >= BASE) a -= BASE; \ 37131377Stjr } while (0) 38230837Sdelphij# define MOD(a) \ 39157043Sdes do { \ 40230837Sdelphij CHOP(a); \ 41230837Sdelphij MOD28(a); \ 42230837Sdelphij } while (0) 43230837Sdelphij# define MOD63(a) \ 44230837Sdelphij do { /* this assumes a is not negative */ \ 45230837Sdelphij z_off64_t tmp = a >> 32; \ 46230837Sdelphij a &= 0xffffffffL; \ 47230837Sdelphij a += (tmp << 8) - (tmp << 5) + tmp; \ 48230837Sdelphij tmp = a >> 16; \ 49230837Sdelphij a &= 0xffffL; \ 50230837Sdelphij a += (tmp << 4) - tmp; \ 51230837Sdelphij tmp = a >> 16; \ 52230837Sdelphij a &= 0xffffL; \ 53230837Sdelphij a += (tmp << 4) - tmp; \ 54157043Sdes if (a >= BASE) a -= BASE; \ 55157043Sdes } while (0) 56131377Stjr#else 57131377Stjr# define MOD(a) a %= BASE 58230837Sdelphij# define MOD28(a) a %= BASE 59230837Sdelphij# define MOD63(a) a %= BASE 60131377Stjr#endif 61131377Stjr 6217651Speter/* ========================================================================= */ 63313796SdelphijuLong ZEXPORT adler32_z(adler, buf, len) 6417651Speter uLong adler; 6517651Speter const Bytef *buf; 66313796Sdelphij z_size_t len; 6717651Speter{ 68157043Sdes unsigned long sum2; 69157043Sdes unsigned n; 7017651Speter 71157043Sdes /* split Adler-32 into component sums */ 72157043Sdes sum2 = (adler >> 16) & 0xffff; 73157043Sdes adler &= 0xffff; 7417651Speter 75157043Sdes /* in case user likes doing a byte at a time, keep it fast */ 76157043Sdes if (len == 1) { 77157043Sdes adler += buf[0]; 78157043Sdes if (adler >= BASE) 79157043Sdes adler -= BASE; 80157043Sdes sum2 += adler; 81157043Sdes if (sum2 >= BASE) 82157043Sdes sum2 -= BASE; 83157043Sdes return adler | (sum2 << 16); 84157043Sdes } 85157043Sdes 86157043Sdes /* initial Adler-32 value (deferred check for len == 1 speed) */ 87157043Sdes if (buf == Z_NULL) 88157043Sdes return 1L; 89157043Sdes 90157043Sdes /* in case short lengths are provided, keep it somewhat fast */ 91157043Sdes if (len < 16) { 92157043Sdes while (len--) { 93157043Sdes adler += *buf++; 94157043Sdes sum2 += adler; 95157043Sdes } 96157043Sdes if (adler >= BASE) 97157043Sdes adler -= BASE; 98230837Sdelphij MOD28(sum2); /* only added so many BASE's */ 99157043Sdes return adler | (sum2 << 16); 100157043Sdes } 101157043Sdes 102157043Sdes /* do length NMAX blocks -- requires just one modulo operation */ 103157043Sdes while (len >= NMAX) { 104157043Sdes len -= NMAX; 105157043Sdes n = NMAX / 16; /* NMAX is divisible by 16 */ 106157043Sdes do { 107157043Sdes DO16(buf); /* 16 sums unrolled */ 108157043Sdes buf += 16; 109157043Sdes } while (--n); 110157043Sdes MOD(adler); 111157043Sdes MOD(sum2); 112157043Sdes } 113157043Sdes 114157043Sdes /* do remaining bytes (less than NMAX, still just one modulo) */ 115157043Sdes if (len) { /* avoid modulos if none remaining */ 116157043Sdes while (len >= 16) { 117157043Sdes len -= 16; 11817651Speter DO16(buf); 119131377Stjr buf += 16; 12017651Speter } 121157043Sdes while (len--) { 122157043Sdes adler += *buf++; 123157043Sdes sum2 += adler; 124157043Sdes } 125157043Sdes MOD(adler); 126157043Sdes MOD(sum2); 12717651Speter } 128157043Sdes 129157043Sdes /* return recombined sums */ 130157043Sdes return adler | (sum2 << 16); 13117651Speter} 132157043Sdes 133157043Sdes/* ========================================================================= */ 134313796SdelphijuLong ZEXPORT adler32(adler, buf, len) 135313796Sdelphij uLong adler; 136313796Sdelphij const Bytef *buf; 137313796Sdelphij uInt len; 138313796Sdelphij{ 139313796Sdelphij return adler32_z(adler, buf, len); 140313796Sdelphij} 141313796Sdelphij 142313796Sdelphij/* ========================================================================= */ 143205194Sdelphijlocal uLong adler32_combine_(adler1, adler2, len2) 144157043Sdes uLong adler1; 145157043Sdes uLong adler2; 146205194Sdelphij z_off64_t len2; 147157043Sdes{ 148157043Sdes unsigned long sum1; 149157043Sdes unsigned long sum2; 150157043Sdes unsigned rem; 151157043Sdes 152230837Sdelphij /* for negative len, return invalid adler32 as a clue for debugging */ 153230837Sdelphij if (len2 < 0) 154230837Sdelphij return 0xffffffffUL; 155230837Sdelphij 156157043Sdes /* the derivation of this formula is left as an exercise for the reader */ 157230837Sdelphij MOD63(len2); /* assumes len2 >= 0 */ 158230837Sdelphij rem = (unsigned)len2; 159157043Sdes sum1 = adler1 & 0xffff; 160157043Sdes sum2 = rem * sum1; 161157043Sdes MOD(sum2); 162157043Sdes sum1 += (adler2 & 0xffff) + BASE - 1; 163157043Sdes sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem; 164205194Sdelphij if (sum1 >= BASE) sum1 -= BASE; 165205194Sdelphij if (sum1 >= BASE) sum1 -= BASE; 166313796Sdelphij if (sum2 >= ((unsigned long)BASE << 1)) sum2 -= ((unsigned long)BASE << 1); 167205194Sdelphij if (sum2 >= BASE) sum2 -= BASE; 168157043Sdes return sum1 | (sum2 << 16); 169157043Sdes} 170205194Sdelphij 171205194Sdelphij/* ========================================================================= */ 172205194SdelphijuLong ZEXPORT adler32_combine(adler1, adler2, len2) 173205194Sdelphij uLong adler1; 174205194Sdelphij uLong adler2; 175205194Sdelphij z_off_t len2; 176205194Sdelphij{ 177205194Sdelphij return adler32_combine_(adler1, adler2, len2); 178205194Sdelphij} 179205194Sdelphij 180205194SdelphijuLong ZEXPORT adler32_combine64(adler1, adler2, len2) 181205194Sdelphij uLong adler1; 182205194Sdelphij uLong adler2; 183205194Sdelphij z_off64_t len2; 184205194Sdelphij{ 185205194Sdelphij return adler32_combine_(adler1, adler2, len2); 186205194Sdelphij} 187