ref: d0ab3a0dd8f6355b3603d0fb04043a9ae867639b
dir: /libfreetype/adler32.c/
/* adler32.c -- compute the Adler-32 checksum of a data stream * Copyright (C) 1995-2002 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h */ /* @(#) $Id: adler32.c,v 1.2 2002/11/06 22:32:54 davidT Exp $ */ #include "zlib.h" #define BASE 65521L /* largest prime smaller than 65536 */ #define NMAX 5552 /* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */ #define DO1(buf,i) {s1 += buf[i]; s2 += s1;} #define DO2(buf,i) DO1(buf,i); DO1(buf,i+1); #define DO4(buf,i) DO2(buf,i); DO2(buf,i+2); #define DO8(buf,i) DO4(buf,i); DO4(buf,i+4); #define DO16(buf) DO8(buf,0); DO8(buf,8); /* ========================================================================= */ ZEXTERNDEF uLong ZEXPORT adler32(adler, buf, len) uLong adler; const Bytef *buf; uInt len; { unsigned long s1 = adler & 0xffff; unsigned long s2 = (adler >> 16) & 0xffff; int k; if (buf == Z_NULL) return 1L; while (len > 0) { k = len < NMAX ? len : NMAX; len -= k; while (k >= 16) { DO16(buf); buf += 16; k -= 16; } if (k != 0) do { s1 += *buf++; s2 += s1; } while (--k); s1 %= BASE; s2 %= BASE; } return (s2 << 16) | s1; }