linux/fs/btrfs/hash.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

/*
 *  Original copy from:
 *  linux/fs/ext3/hash.c
 *
 * Copyright (C) 2002 by Theodore Ts'o
 *
 * This file is released under the GPL v2.
 *
 * This file may be redistributed under the terms of the GNU Public
 * License.
 */

#include <linux/types.h>
#include "hash.h"
#define DELTA 0x9E3779B9

static void TEA_transform(__u32 buf[2], __u32 const in[])
{
	__u32	sum = 0;
	__u32	b0 = buf[0], b1 = buf[1];
	__u32	a = in[0], b = in[1], c = in[2], d = in[3];
	int	n = 16;

	do {
		sum += DELTA;
		b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b);
		b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d);
	} while(--n);

	buf[0] += b0;
	buf[1] += b1;
}

static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
{
	__u32	pad, val;
	int	i;

	pad = (__u32)len | ((__u32)len << 8);
	pad |= pad << 16;

	val = pad;
	if (len > num*4)
		len = num * 4;
	for (i=0; i < len; i++) {
		if ((i % 4) == 0)
			val = pad;
		val = msg[i] + (val << 8);
		if ((i % 4) == 3) {
			*buf++ = val;
			val = pad;
			num--;
		}
	}
	if (--num >= 0)
		*buf++ = val;
	while (--num >= 0)
		*buf++ = pad;
}

u64 btrfs_name_hash(const char *name, int len)
{
	__u32	hash;
	__u32	minor_hash = 0;
	const char	*p;
	__u32		in[8], buf[4];
	u64		hash_result;

	if (len == 1 && *name == '.') {
		return 1;
	} else if (len == 2 && name[0] == '.' && name[1] == '.') {
		return 2;
	}

	/* Initialize the default seed for the hash checksum functions */
	buf[0] = 0x67452301;
	buf[1] = 0xefcdab89;
	buf[2] = 0x98badcfe;
	buf[3] = 0x10325476;

	p = name;
	while (len > 0) {
		str2hashbuf(p, len, in, 4);
		TEA_transform(buf, in);
		len -= 16;
		p += 16;
	}
	hash = buf[0];
	minor_hash = buf[1];
	hash_result = buf[0];
	hash_result <<= 32;
	hash_result |= buf[1];
	return hash_result;
}