Root/fs/ext4/hash.c

1/*
2 * linux/fs/ext4/hash.c
3 *
4 * Copyright (C) 2002 by Theodore Ts'o
5 *
6 * This file is released under the GPL v2.
7 *
8 * This file may be redistributed under the terms of the GNU Public
9 * License.
10 */
11
12#include <linux/fs.h>
13#include <linux/jbd2.h>
14#include <linux/cryptohash.h>
15#include "ext4.h"
16
17#define DELTA 0x9E3779B9
18
19static void TEA_transform(__u32 buf[4], __u32 const in[])
20{
21    __u32 sum = 0;
22    __u32 b0 = buf[0], b1 = buf[1];
23    __u32 a = in[0], b = in[1], c = in[2], d = in[3];
24    int n = 16;
25
26    do {
27        sum += DELTA;
28        b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b);
29        b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d);
30    } while (--n);
31
32    buf[0] += b0;
33    buf[1] += b1;
34}
35
36
37/* The old legacy hash */
38static __u32 dx_hack_hash_unsigned(const char *name, int len)
39{
40    __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
41    const unsigned char *ucp = (const unsigned char *) name;
42
43    while (len--) {
44        hash = hash1 + (hash0 ^ (((int) *ucp++) * 7152373));
45
46        if (hash & 0x80000000)
47            hash -= 0x7fffffff;
48        hash1 = hash0;
49        hash0 = hash;
50    }
51    return hash0 << 1;
52}
53
54static __u32 dx_hack_hash_signed(const char *name, int len)
55{
56    __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
57    const signed char *scp = (const signed char *) name;
58
59    while (len--) {
60        hash = hash1 + (hash0 ^ (((int) *scp++) * 7152373));
61
62        if (hash & 0x80000000)
63            hash -= 0x7fffffff;
64        hash1 = hash0;
65        hash0 = hash;
66    }
67    return hash0 << 1;
68}
69
70static void str2hashbuf_signed(const char *msg, int len, __u32 *buf, int num)
71{
72    __u32 pad, val;
73    int i;
74    const signed char *scp = (const signed char *) msg;
75
76    pad = (__u32)len | ((__u32)len << 8);
77    pad |= pad << 16;
78
79    val = pad;
80    if (len > num*4)
81        len = num * 4;
82    for (i = 0; i < len; i++) {
83        if ((i % 4) == 0)
84            val = pad;
85        val = ((int) scp[i]) + (val << 8);
86        if ((i % 4) == 3) {
87            *buf++ = val;
88            val = pad;
89            num--;
90        }
91    }
92    if (--num >= 0)
93        *buf++ = val;
94    while (--num >= 0)
95        *buf++ = pad;
96}
97
98static void str2hashbuf_unsigned(const char *msg, int len, __u32 *buf, int num)
99{
100    __u32 pad, val;
101    int i;
102    const unsigned char *ucp = (const unsigned char *) msg;
103
104    pad = (__u32)len | ((__u32)len << 8);
105    pad |= pad << 16;
106
107    val = pad;
108    if (len > num*4)
109        len = num * 4;
110    for (i = 0; i < len; i++) {
111        if ((i % 4) == 0)
112            val = pad;
113        val = ((int) ucp[i]) + (val << 8);
114        if ((i % 4) == 3) {
115            *buf++ = val;
116            val = pad;
117            num--;
118        }
119    }
120    if (--num >= 0)
121        *buf++ = val;
122    while (--num >= 0)
123        *buf++ = pad;
124}
125
126/*
127 * Returns the hash of a filename. If len is 0 and name is NULL, then
128 * this function can be used to test whether or not a hash version is
129 * supported.
130 *
131 * The seed is an 4 longword (32 bits) "secret" which can be used to
132 * uniquify a hash. If the seed is all zero's, then some default seed
133 * may be used.
134 *
135 * A particular hash version specifies whether or not the seed is
136 * represented, and whether or not the returned hash is 32 bits or 64
137 * bits. 32 bit hashes will return 0 for the minor hash.
138 */
139int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
140{
141    __u32 hash;
142    __u32 minor_hash = 0;
143    const char *p;
144    int i;
145    __u32 in[8], buf[4];
146    void (*str2hashbuf)(const char *, int, __u32 *, int) =
147                str2hashbuf_signed;
148
149    /* Initialize the default seed for the hash checksum functions */
150    buf[0] = 0x67452301;
151    buf[1] = 0xefcdab89;
152    buf[2] = 0x98badcfe;
153    buf[3] = 0x10325476;
154
155    /* Check to see if the seed is all zero's */
156    if (hinfo->seed) {
157        for (i = 0; i < 4; i++) {
158            if (hinfo->seed[i])
159                break;
160        }
161        if (i < 4)
162            memcpy(buf, hinfo->seed, sizeof(buf));
163    }
164
165    switch (hinfo->hash_version) {
166    case DX_HASH_LEGACY_UNSIGNED:
167        hash = dx_hack_hash_unsigned(name, len);
168        break;
169    case DX_HASH_LEGACY:
170        hash = dx_hack_hash_signed(name, len);
171        break;
172    case DX_HASH_HALF_MD4_UNSIGNED:
173        str2hashbuf = str2hashbuf_unsigned;
174    case DX_HASH_HALF_MD4:
175        p = name;
176        while (len > 0) {
177            (*str2hashbuf)(p, len, in, 8);
178            half_md4_transform(buf, in);
179            len -= 32;
180            p += 32;
181        }
182        minor_hash = buf[2];
183        hash = buf[1];
184        break;
185    case DX_HASH_TEA_UNSIGNED:
186        str2hashbuf = str2hashbuf_unsigned;
187    case DX_HASH_TEA:
188        p = name;
189        while (len > 0) {
190            (*str2hashbuf)(p, len, in, 4);
191            TEA_transform(buf, in);
192            len -= 16;
193            p += 16;
194        }
195        hash = buf[0];
196        minor_hash = buf[1];
197        break;
198    default:
199        hinfo->hash = 0;
200        return -1;
201    }
202    hash = hash & ~1;
203    if (hash == (EXT4_HTREE_EOF << 1))
204        hash = (EXT4_HTREE_EOF-1) << 1;
205    hinfo->hash = hash;
206    hinfo->minor_hash = minor_hash;
207    return 0;
208}
209

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