linux/fs/ext4/hash.c
<<
>>
Prefs
   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_32BIT << 1))
 204                hash = (EXT4_HTREE_EOF_32BIT - 1) << 1;
 205        hinfo->hash = hash;
 206        hinfo->minor_hash = minor_hash;
 207        return 0;
 208}
 209
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.