adler32.c File Reference

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "misc/util/abc_global.h"
#include "zutil.h"

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Macros
#define	local   static
#define	BASE   65521UL /* largest prime smaller than 65536 */
#define	NMAX   5552
#define	DO1(buf, i)
#define	DO2(buf, i)
#define	DO4(buf, i)
#define	DO8(buf, i)
#define	DO16(buf)
#define	MOD(a)
#define	MOD4(a)

Functions
local uLong	adler32_combine_ (uLong adler1, uLong adler2, z_off64_t len2)
uLong ZEXPORT	adler32 (uLong adler, const Bytef *buf, uInt len)
uLong ZEXPORT	adler32_combine (uLong adler1, uLong adler2, z_off_t len2)
uLong ZEXPORT	adler32_combine64 (uLong adler1, uLong adler2, z_off64_t len2)

Macro Definition Documentation

BASE

#define BASE   65521UL /* largest prime smaller than 65536 */

Definition at line 21 of file adler32.c.

DO1

#define DO1	(		buf,
			i )

Value:

{adler += (buf)[i]; sum2 += adler;}

Definition at line 25 of file adler32.c.

DO16

#define DO16

(

buf

)

Value:

DO8(buf,0); DO8(buf,8);

Definition at line 29 of file adler32.c.

DO2

#define DO2	(		buf,
			i )

Value:

DO1(buf,i); DO1(buf,i+1);

Definition at line 26 of file adler32.c.

DO4

#define DO4	(		buf,
			i )

Value:

DO2(buf,i); DO2(buf,i+2);

Definition at line 27 of file adler32.c.

DO8

#define DO8	(		buf,
			i )

Value:

DO4(buf,i); DO4(buf,i+4);

Definition at line 28 of file adler32.c.

local

#define local   static

Definition at line 17 of file adler32.c.

MOD

#define MOD

(

a

)

Value:

a %= BASE

Definition at line 62 of file adler32.c.

MOD4

#define MOD4

(

a

)

Value:

a %= BASE

Definition at line 63 of file adler32.c.

NMAX

#define NMAX   5552

Definition at line 22 of file adler32.c.

Function Documentation

adler32()

uLong ZEXPORT adler32	(	uLong	adler,
		const Bytef *	buf,
		uInt	len )

Definition at line 67 of file adler32.c.

{
    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);
}

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adler32_combine()

uLong ZEXPORT adler32_combine	(	uLong	adler1,
		uLong	adler2,
		z_off_t	len2 )

Definition at line 156 of file adler32.c.

{
    return adler32_combine_(adler1, adler2, len2);
}

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adler32_combine64()

uLong ZEXPORT adler32_combine64	(	uLong	adler1,
		uLong	adler2,
		z_off64_t	len2 )

Definition at line 161 of file adler32.c.

{
    return adler32_combine_(adler1, adler2, len2);
}

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adler32_combine_()

local uLong adler32_combine_	(	uLong	adler1,
		uLong	adler2,
		z_off64_t	len2 )

Definition at line 135 of file adler32.c.

{
    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);
}

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