src/zlib/adler32.c

/* adler32.c -- compute the Adler-32 checksum of a data stream
 * Copyright (C) 1995-2004 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)  {adler += (buf)[i]; sum2 += adler;}
#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);

/* use NO_DIVIDE if your processor does not do division in hardware */
#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)
#  define MOD4(a) \
    do { \
        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
#  define MOD4(a) a %= BASE
#endif

/* ========================================================================= */
uLong ZEXPORT adler32(adler, buf, len)
    uLong adler;
    const Bytef *buf;
    uInt len;
{
    unsigned long sum2;
    unsigned n;

    /* split Adler-32 into component sums */
    sum2 = (adler >> 16) & 0xffff;
    adler &= 0xffff;

    /* in case user likes doing a byte at a time, keep it fast */
    if (len == 1) {
        adler += buf[0];
        if (adler >= BASE)
            adler -= BASE;
        sum2 += adler;
        if (sum2 >= BASE)
            sum2 -= BASE;
        return adler | (sum2 << 16);
    }

    /* initial Adler-32 value (deferred check for len == 1 speed) */
    if (buf == Z_NULL)
        return 1L;

    /* in case short lengths are provided, keep it somewhat fast */
    if (len < 16) {
        while (len--) {
            adler += *buf++;
            sum2 += adler;
        }
        if (adler >= BASE)
            adler -= BASE;
        MOD4(sum2);             /* only added so many BASE's */
        return adler | (sum2 << 16);
    }

    /* do length NMAX blocks -- requires just one modulo operation */
    while (len >= NMAX) {
        len -= NMAX;
        n = NMAX / 16;          /* NMAX is divisible by 16 */
        do {
            DO16(buf);          /* 16 sums unrolled */
            buf += 16;
        } while (--n);
        MOD(adler);
        MOD(sum2);
    }

    /* do remaining bytes (less than NMAX, still just one modulo) */
    if (len) {                  /* avoid modulos if none remaining */
        while (len >= 16) {
            len -= 16;
            DO16(buf);
            buf += 16;
        }
        while (len--) {
            adler += *buf++;
            sum2 += adler;
        }
        MOD(adler);
        MOD(sum2);
    }

    /* return recombined sums */
    return adler | (sum2 << 16);
}

/* ========================================================================= */
uLong ZEXPORT adler32_combine(adler1, adler2, len2)
    uLong adler1;
    uLong adler2;
    z_off_t len2;
{
    unsigned long sum1;
    unsigned long sum2;
    unsigned rem;

    /* the derivation of this formula is left as an exercise for the reader */
    rem = (unsigned)(len2 % BASE);
    sum1 = adler1 & 0xffff;
    sum2 = rem * sum1;
    MOD(sum2);
    sum1 += (adler2 & 0xffff) + BASE - 1;
    sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
    if (sum1 > BASE) sum1 -= BASE;
    if (sum1 > BASE) sum1 -= BASE;
    if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
    if (sum2 > BASE) sum2 -= BASE;
    return sum1 | (sum2 << 16);
}
Commit	Line	Data
	1	/* adler32.c -- compute the Adler-32 checksum of a data stream
	2	* Copyright (C) 1995-2004 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) {adler += (buf)[i]; sum2 += adler;}
	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	/* use NO_DIVIDE if your processor does not do division in hardware */
	22	#ifdef NO_DIVIDE
	23	# define MOD(a) \
	24	do { \
	25	if (a >= (BASE << 16)) a -= (BASE << 16); \
	26	if (a >= (BASE << 15)) a -= (BASE << 15); \
	27	if (a >= (BASE << 14)) a -= (BASE << 14); \
	28	if (a >= (BASE << 13)) a -= (BASE << 13); \
	29	if (a >= (BASE << 12)) a -= (BASE << 12); \
	30	if (a >= (BASE << 11)) a -= (BASE << 11); \
	31	if (a >= (BASE << 10)) a -= (BASE << 10); \
	32	if (a >= (BASE << 9)) a -= (BASE << 9); \
	33	if (a >= (BASE << 8)) a -= (BASE << 8); \
	34	if (a >= (BASE << 7)) a -= (BASE << 7); \
	35	if (a >= (BASE << 6)) a -= (BASE << 6); \
	36	if (a >= (BASE << 5)) a -= (BASE << 5); \
	37	if (a >= (BASE << 4)) a -= (BASE << 4); \
	38	if (a >= (BASE << 3)) a -= (BASE << 3); \
	39	if (a >= (BASE << 2)) a -= (BASE << 2); \
	40	if (a >= (BASE << 1)) a -= (BASE << 1); \
	41	if (a >= BASE) a -= BASE; \
	42	} while (0)
	43	# define MOD4(a) \
	44	do { \
	45	if (a >= (BASE << 4)) a -= (BASE << 4); \
	46	if (a >= (BASE << 3)) a -= (BASE << 3); \
	47	if (a >= (BASE << 2)) a -= (BASE << 2); \
	48	if (a >= (BASE << 1)) a -= (BASE << 1); \
	49	if (a >= BASE) a -= BASE; \
	50	} while (0)
	51	#else
	52	# define MOD(a) a %= BASE
	53	# define MOD4(a) a %= BASE
	54	#endif
	55
	56	/* ========================================================================= */
	57	uLong ZEXPORT adler32(adler, buf, len)
	58	uLong adler;
	59	const Bytef *buf;
	60	uInt len;
	61	{
	62	unsigned long sum2;
	63	unsigned n;
	64
	65	/* split Adler-32 into component sums */
	66	sum2 = (adler >> 16) & 0xffff;
	67	adler &= 0xffff;
	68
	69	/* in case user likes doing a byte at a time, keep it fast */
	70	if (len == 1) {
	71	adler += buf[0];
	72	if (adler >= BASE)
	73	adler -= BASE;
	74	sum2 += adler;
	75	if (sum2 >= BASE)
	76	sum2 -= BASE;
	77	return adler \| (sum2 << 16);
	78	}
	79
	80	/* initial Adler-32 value (deferred check for len == 1 speed) */
	81	if (buf == Z_NULL)
	82	return 1L;
	83
	84	/* in case short lengths are provided, keep it somewhat fast */
	85	if (len < 16) {
	86	while (len--) {
	87	adler += *buf++;
	88	sum2 += adler;
	89	}
	90	if (adler >= BASE)
	91	adler -= BASE;
	92	MOD4(sum2); /* only added so many BASE's */
	93	return adler \| (sum2 << 16);
	94	}
	95
	96	/* do length NMAX blocks -- requires just one modulo operation */
	97	while (len >= NMAX) {
	98	len -= NMAX;
	99	n = NMAX / 16; /* NMAX is divisible by 16 */
	100	do {
	101	DO16(buf); /* 16 sums unrolled */
	102	buf += 16;
	103	} while (--n);
	104	MOD(adler);
	105	MOD(sum2);
	106	}
	107
	108	/* do remaining bytes (less than NMAX, still just one modulo) */
	109	if (len) { /* avoid modulos if none remaining */
	110	while (len >= 16) {
	111	len -= 16;
	112	DO16(buf);
	113	buf += 16;
	114	}
	115	while (len--) {
	116	adler += *buf++;
	117	sum2 += adler;
	118	}
	119	MOD(adler);
	120	MOD(sum2);
	121	}
	122
	123	/* return recombined sums */
	124	return adler \| (sum2 << 16);
	125	}
	126
	127	/* ========================================================================= */
	128	uLong ZEXPORT adler32_combine(adler1, adler2, len2)
	129	uLong adler1;
	130	uLong adler2;
	131	z_off_t len2;
	132	{
	133	unsigned long sum1;
	134	unsigned long sum2;
	135	unsigned rem;
	136
	137	/* the derivation of this formula is left as an exercise for the reader */
	138	rem = (unsigned)(len2 % BASE);
	139	sum1 = adler1 & 0xffff;
	140	sum2 = rem * sum1;
	141	MOD(sum2);
	142	sum1 += (adler2 & 0xffff) + BASE - 1;
	143	sum2 += ((adler1 >> 16) & 0xffff) + ((adler2 >> 16) & 0xffff) + BASE - rem;
	144	if (sum1 > BASE) sum1 -= BASE;
	145	if (sum1 > BASE) sum1 -= BASE;
	146	if (sum2 > (BASE << 1)) sum2 -= (BASE << 1);
	147	if (sum2 > BASE) sum2 -= BASE;
	148	return sum1 \| (sum2 << 16);
	149	}