adler32.c File Reference

Compute the Adler-32 checksum of a data stream. More...

#include "zutil.h"

Macros
#define	BASE   65521U /* largest prime smaller than 65536 */
#define	NMAX   5552
#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);
#define	MOD(a)   a %= BASE
#define	MOD28(a)   a %= BASE
#define	MOD63(a)   a %= BASE

Functions
uLong ZEXPORT	adler32_z (uLong adler, const Bytef *buf, z_size_t len)
	Same as adler32(), but with a size_t length.
uLong ZEXPORT	adler32 (uLong adler, const Bytef *buf, uInt len)
	Update a running Adler-32 checksum with the bytes buf[0..len-1] and return the updated checksum.
local uLong	adler32_combine_ (uLong adler1, uLong adler2, z_off64_t len2)
	Combine two Adler-32 checksums into one.
uLong ZEXPORT	adler32_combine (uLong adler1, uLong adler2, z_off_t len2)
uLong ZEXPORT	adler32_combine64 (uLong adler1, uLong adler2, z_off64_t len2)

Detailed Description

Compute the Adler-32 checksum of a data stream.

Copyright (C) 1995-2011, 2016 Mark Adler For conditions of distribution and use, see copyright notice in zlib.h

Function Documentation

adler32()

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

Update a running Adler-32 checksum with the bytes buf[0..len-1] and return the updated checksum.

An Adler-32 value is in the range of a 32-bit unsigned integer. If buf is Z_NULL, this function returns the required initial value for the checksum.

An Adler-32 checksum is almost as reliable as a CRC-32 but can be computed much faster.

Usage example:

uLong adler = adler32(0L, Z_NULL, 0);
 
while (read_buffer(buffer, length) != EOF) {
  adler = adler32(adler, buffer, length);
}
if (adler != original_adler) error();

adler32_combine_()

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

Combine two Adler-32 checksums into one.

For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, Adler-32 checksums were calculated for each, adler1 and adler2. adler32_combine() returns the Adler-32 checksum of seq1 and seq2 concatenated, requiring only adler1, adler2, and len2.

Note that the z_off_t type (like off_t) is a signed integer. If len2 is negative, the result has no meaning or utility.