[netwatch.git] / lib / crc32.c

#include <stdint.h>

/* code from http://www.faqs.org/faqs/compression-faq/part1/section-26.html,
 * presumed public domain */

uint32_t crc32_table[256];

uint32_t crc32(uint8_t *buf, int len)
{
	uint8_t *p;
	uint32_t crc;

	crc = 0xffffffff;       /* preload shift register, per CRC-32 spec */
	for (p = buf; len > 0; ++p, --len)
		crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
	return ~crc;	    /* transmit complement, per CRC-32 spec */
}

/*
 * Build auxiliary table for parallel byte-at-a-time CRC-32.
 */
#define CRC32_POLY 0x04c11db7     /* AUTODIN II, Ethernet, & FDDI */

void crc32_init()
{
	int i, j;
	uint32_t c;

	for (i = 0; i < 256; ++i) {
		for (c = i << 24, j = 8; j > 0; --j)
			c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1);
		crc32_table[i] = c;
	}
}
Commit	Line	Data
74032dae JW	1	#include <stdint.h>
	2
	3	/* code from http://www.faqs.org/faqs/compression-faq/part1/section-26.html,
	4	* presumed public domain */
	5
	6	uint32_t crc32_table[256];
	7
	8	uint32_t crc32(uint8_t *buf, int len)
	9	{
	10	uint8_t *p;
	11	uint32_t crc;
	12
	13	crc = 0xffffffff; /* preload shift register, per CRC-32 spec */
	14	for (p = buf; len > 0; ++p, --len)
	15	crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
	16	return ~crc; /* transmit complement, per CRC-32 spec */
	17	}
	18
	19	/*
	20	* Build auxiliary table for parallel byte-at-a-time CRC-32.
	21	*/
	22	#define CRC32_POLY 0x04c11db7 /* AUTODIN II, Ethernet, & FDDI */
	23
	24	void crc32_init()
	25	{
	26	int i, j;
	27	uint32_t c;
	28
	29	for (i = 0; i < 256; ++i) {
	30	for (c = i << 24, j = 8; j > 0; --j)
	31	c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1);
	32	crc32_table[i] = c;
	33	}
	34	}