hash.c

模仿cisco路由器

/*
	Copyright (C) 2002, 2003 Slava Astashonok <[e-mail]>

	This program is free software; you can redistribute it and/or
	modify it under the terms of the GNU General Public License.

	$Id: hash.c,v 1.3.2.1 2003/03/28 22:57:51 sla Exp $
*/

#include <common.h>

#include <hash.h>

#ifdef HASH_TYPE_CRC
static uint16_t crc16_table[256];

uint16_t crc16(uint16_t crc, uint8_t val)
{
	int i;

	crc ^= val << 8;
	for (i = 8; i--; )
		crc = crc & 0x8000 ? (crc << 1) ^ CRC16_POLY : crc << 1;
	return crc;
}
#endif

hash_t hash(void *p, int size)
{
	/*
	?FIXME?
	Check for valid size (> 0)
	*/

	hash_t hash = 0;

#if defined HASH_TYPE_XOR && HASH_BITS == 16
	size--;
#endif

	for (;size--;) {
#ifdef HASH_TYPE_XOR
		hash ^= *((hash_t *)p++);
#endif
#ifdef HASH_TYPE_CRC
		hash = crc16_table[*((uint8_t *)p++) ^ (hash >> 8)] ^ (hash << 8);
#endif
	}
	return hash;
}

void hash_init()
{
#ifdef HASH_TYPE_CRC
	int i;
	for (i = 0; i < 256 ; i++) crc16_table[i] = crc16(0, i);
#endif
}