hash.c revision 1.2 
1/*	$Id: hash.c,v 1.2 2019/02/10 23:24:14 benno Exp $ */
2/*
3 * Copyright (c) 2019 Kristaps Dzonsons <kristaps@bsd.lv>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17#include <sys/types.h>
18
19#include <assert.h>
20#include <endian.h>
21#include <stdint.h>
22#include <stdlib.h>
23
24#include "extern.h"
25#include "md4.h"
26
27/*
28 * A fast 32-bit hash.
29 * Described in Tridgell's "Efficient Algorithms for Sorting and
30 * Synchronization" thesis and the "Rolling checksum" document.
31 */
32uint32_t
33hash_fast(const void *buf, size_t len)
34{
35	size_t			 i = 0;
36	uint32_t		 a = 0, /* part of a(k, l) */
37				 b = 0; /* b(k, l) */
38	const signed char	*dat = buf;
39
40	if (len > 4)
41		for ( ; i < len - 4; i += 4) {
42			b += 4 * (a + dat[i]) +
43			    3 * dat[i + 1] +
44			    2 * dat[i + 2] +
45			    dat[i + 3];
46			a += dat[i + 0] +
47			    dat[i + 1] +
48			    dat[i + 2] +
49			    dat[i + 3];
50		}
51
52	for ( ; i < len; i++) {
53		a += dat[i];
54		b += a;
55	}
56
57	/* s(k, l) = (eps % M) + 2^16 b(k, l) % M */
58
59	return (a & 0xffff) + (b << 16);
60}
61
62/*
63 * Slow MD4-based hash with trailing seed.
64 */
65void
66hash_slow(const void *buf, size_t len,
67	unsigned char *md, const struct sess *sess)
68{
69	MD4_CTX		 ctx;
70	int32_t		 seed = htole32(sess->seed);
71
72	MD4_Init(&ctx);
73	MD4_Update(&ctx, buf, len);
74	MD4_Update(&ctx, (unsigned char *)&seed, sizeof(int32_t));
75	MD4_Final(md, &ctx);
76}
77
78/*
79 * Hash an entire file.
80 * This is similar to hash_slow() except the seed is hashed at the end
81 * of the sequence, not the beginning.
82 */
83void
84hash_file(const void *buf, size_t len,
85	unsigned char *md, const struct sess *sess)
86{
87	MD4_CTX		 ctx;
88	int32_t		 seed = htole32(sess->seed);
89
90	MD4_Init(&ctx);
91	MD4_Update(&ctx, (unsigned char *)&seed, sizeof(int32_t));
92	MD4_Update(&ctx, buf, len);
93	MD4_Final(md, &ctx);
94}
95