src/zlib/adler32.c

/* adler32.c -- compute the Adler-32 checksum of a data stream
 * Copyright (C) 1995-2003 Mark Adler
 * For conditions of distribution and use, see copyright notice in zlib.h
 */

/* @(#) $Id$ */

#define ZLIB_INTERNAL
#include "zlib.h"

#define BASE 65521UL    /* 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);

#ifdef NO_DIVIDE
#  define MOD(a) \
    do { \
        if (a >= (BASE << 16)) a -= (BASE << 16); \
        if (a >= (BASE << 15)) a -= (BASE << 15); \
        if (a >= (BASE << 14)) a -= (BASE << 14); \
        if (a >= (BASE << 13)) a -= (BASE << 13); \
        if (a >= (BASE << 12)) a -= (BASE << 12); \
        if (a >= (BASE << 11)) a -= (BASE << 11); \
        if (a >= (BASE << 10)) a -= (BASE << 10); \
        if (a >= (BASE << 9)) a -= (BASE << 9); \
        if (a >= (BASE << 8)) a -= (BASE << 8); \
        if (a >= (BASE << 7)) a -= (BASE << 7); \
        if (a >= (BASE << 6)) a -= (BASE << 6); \
        if (a >= (BASE << 5)) a -= (BASE << 5); \
        if (a >= (BASE << 4)) a -= (BASE << 4); \
        if (a >= (BASE << 3)) a -= (BASE << 3); \
        if (a >= (BASE << 2)) a -= (BASE << 2); \
        if (a >= (BASE << 1)) a -= (BASE << 1); \
        if (a >= BASE) a -= BASE; \
    } while (0)
#else
#  define MOD(a) a %= BASE
#endif

/* ========================================================================= */
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 ? (int)len : NMAX;
        len -= k;
        while (k >= 16) {
            DO16(buf);
            buf += 16;
            k -= 16;
        }
        if (k != 0) do {
            s1 += *buf++;
            s2 += s1;
        } while (--k);
        MOD(s1);
        MOD(s2);
    }
    return (s2 << 16) | s1;
}
Commit	Line	Data
	1	/* adler32.c -- compute the Adler-32 checksum of a data stream
	2	* Copyright (C) 1995-2003 Mark Adler
	3	* For conditions of distribution and use, see copyright notice in zlib.h
	4	*/
	5
	6	/* @(#) $Id$ */
	7
	8	#define ZLIB_INTERNAL
	9	#include "zlib.h"
	10
	11	#define BASE 65521UL /* largest prime smaller than 65536 */
	12	#define NMAX 5552
	13	/* NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1 */
	14
	15	#define DO1(buf,i) {s1 += buf[i]; s2 += s1;}
	16	#define DO2(buf,i) DO1(buf,i); DO1(buf,i+1);
	17	#define DO4(buf,i) DO2(buf,i); DO2(buf,i+2);
	18	#define DO8(buf,i) DO4(buf,i); DO4(buf,i+4);
	19	#define DO16(buf) DO8(buf,0); DO8(buf,8);
	20
	21	#ifdef NO_DIVIDE
	22	# define MOD(a) \
	23	do { \
	24	if (a >= (BASE << 16)) a -= (BASE << 16); \
	25	if (a >= (BASE << 15)) a -= (BASE << 15); \
	26	if (a >= (BASE << 14)) a -= (BASE << 14); \
	27	if (a >= (BASE << 13)) a -= (BASE << 13); \
	28	if (a >= (BASE << 12)) a -= (BASE << 12); \
	29	if (a >= (BASE << 11)) a -= (BASE << 11); \
	30	if (a >= (BASE << 10)) a -= (BASE << 10); \
	31	if (a >= (BASE << 9)) a -= (BASE << 9); \
	32	if (a >= (BASE << 8)) a -= (BASE << 8); \
	33	if (a >= (BASE << 7)) a -= (BASE << 7); \
	34	if (a >= (BASE << 6)) a -= (BASE << 6); \
	35	if (a >= (BASE << 5)) a -= (BASE << 5); \
	36	if (a >= (BASE << 4)) a -= (BASE << 4); \
	37	if (a >= (BASE << 3)) a -= (BASE << 3); \
	38	if (a >= (BASE << 2)) a -= (BASE << 2); \
	39	if (a >= (BASE << 1)) a -= (BASE << 1); \
	40	if (a >= BASE) a -= BASE; \
	41	} while (0)
	42	#else
	43	# define MOD(a) a %= BASE
	44	#endif
	45
	46	/* ========================================================================= */
	47	uLong ZEXPORT adler32(adler, buf, len)
	48	uLong adler;
	49	const Bytef *buf;
	50	uInt len;
	51	{
	52	unsigned long s1 = adler & 0xffff;
	53	unsigned long s2 = (adler >> 16) & 0xffff;
	54	int k;
	55
	56	if (buf == Z_NULL) return 1L;
	57
	58	while (len > 0) {
	59	k = len < NMAX ? (int)len : NMAX;
	60	len -= k;
	61	while (k >= 16) {
	62	DO16(buf);
	63	buf += 16;
	64	k -= 16;
	65	}
	66	if (k != 0) do {
	67	s1 += *buf++;
	68	s2 += s1;
	69	} while (--k);
	70	MOD(s1);
	71	MOD(s2);
	72	}
	73	return (s2 << 16) \| s1;
	74	}