crc32.c File Reference

Compute the CRC-32 of a data stream. More...

#include "zutil.h"
#include "crc32.h"

Macros
#define	N   5
#define	W   4
#define	POLY   0xedb88320 /* p(x) reflected, with x^32 implied */

Functions
local z_crc_t	multmodp (z_crc_t a, z_crc_t b)
local z_crc_t	x2nmodp (z_off64_t n, unsigned k)
const z_crc_t FAR *ZEXPORT	get_crc_table (void)
unsigned long ZEXPORT	crc32_z (unsigned long crc, const unsigned char FAR *buf, z_size_t len)
	Same as crc32(), but with a size_t length.
unsigned long ZEXPORT	crc32 (unsigned long crc, const unsigned char FAR *buf, uInt len)
	Update a running CRC-32 with the bytes buf[0..len-1] and return the updated CRC-32.
uLong ZEXPORT	crc32_combine64 (uLong crc1, uLong crc2, z_off64_t len2)
uLong ZEXPORT	crc32_combine (uLong crc1, uLong crc2, z_off_t len2)
	Combine two CRC-32 check values into one.
uLong ZEXPORT	crc32_combine_gen64 (z_off64_t len2)
uLong ZEXPORT	crc32_combine_gen (z_off_t len2)
uLong ZEXPORT	crc32_combine_op (uLong crc1, uLong crc2, uLong op)
	Give the same result as crc32_combine(), using op in place of len2.

Detailed Description

Compute the CRC-32 of a data stream.

Copyright (C) 1995-2022 Mark Adler For conditions of distribution and use, see copyright notice in zlib.h

This interleaved implementation of a CRC makes use of pipelined multiple arithmetic-logic units, commonly found in modern CPU cores. It is due to Kadatch and Jenkins (2010). See doc/crc-doc.1.0.pdf in this distribution.

Function Documentation

crc32()

unsigned long ZEXPORT crc32	(	unsigned long	crc,
		const unsigned char FAR *	buf,
		uInt	len
	)

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

A CRC-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 crc. Pre- and post-conditioning (one's complement) is performed within this function so it shouldn't be done by the application.

Usage example:

uLong crc = crc32(0L, Z_NULL, 0);
 
while (read_buffer(buffer, length) != EOF) {
  crc = crc32(crc, buffer, length);
}
if (crc != original_crc) error();

crc32_combine()

uLong ZEXPORT crc32_combine	(	uLong	crc1,
		uLong	crc2,
		z_off_t	len2
	)

Combine two CRC-32 check values into one.

For two sequences of bytes, seq1 and seq2 with lengths len1 and len2, CRC-32 check values were calculated for each, crc1 and crc2. crc32_combine() returns the CRC-32 check value of seq1 and seq2 concatenated, requiring only crc1, crc2, and len2.

crc32_combine_op()

uLong ZEXPORT crc32_combine_op	(	uLong	crc1,
		uLong	crc2,
		uLong	op
	)

Give the same result as crc32_combine(), using op in place of len2.

op is is generated from len2 by crc32_combine_gen(). This will be faster than crc32_combine() if the generated op is used more than once.