LXR linux/fs/ext3/hash.c

   1/*
   2 *  linux/fs/ext3/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/jbd.h>
  14#include <linux/ext3_fs.h>
  15#include <linux/cryptohash.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 (const char *name, int len)
  39{
  40        __u32 hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
  41        while (len--) {
  42                __u32 hash = hash1 + (hash0 ^ (*name++ * 7152373));
  43
  44                if (hash & 0x80000000) hash -= 0x7fffffff;
  45                hash1 = hash0;
  46                hash0 = hash;
  47        }
  48        return (hash0 << 1);
  49}
  50
  51static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
  52{
  53        __u32   pad, val;
  54        int     i;
  55
  56        pad = (__u32)len | ((__u32)len << 8);
  57        pad |= pad << 16;
  58
  59        val = pad;
  60        if (len > num*4)
  61                len = num * 4;
  62        for (i=0; i < len; i++) {
  63                if ((i % 4) == 0)
  64                        val = pad;
  65                val = msg[i] + (val << 8);
  66                if ((i % 4) == 3) {
  67                        *buf++ = val;
  68                        val = pad;
  69                        num--;
  70                }
  71        }
  72        if (--num >= 0)
  73                *buf++ = val;
  74        while (--num >= 0)
  75                *buf++ = pad;
  76}
  77
  78/*
  79 * Returns the hash of a filename.  If len is 0 and name is NULL, then
  80 * this function can be used to test whether or not a hash version is
  81 * supported.
  82 *
  83 * The seed is an 4 longword (32 bits) "secret" which can be used to
  84 * uniquify a hash.  If the seed is all zero's, then some default seed
  85 * may be used.
  86 *
  87 * A particular hash version specifies whether or not the seed is
  88 * represented, and whether or not the returned hash is 32 bits or 64
  89 * bits.  32 bit hashes will return 0 for the minor hash.
  90 */
  91int ext3fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
  92{
  93        __u32   hash;
  94        __u32   minor_hash = 0;
  95        const char      *p;
  96        int             i;
  97        __u32           in[8], buf[4];
  98
  99        /* Initialize the default seed for the hash checksum functions */
 100        buf[0] = 0x67452301;
 101        buf[1] = 0xefcdab89;
 102        buf[2] = 0x98badcfe;
 103        buf[3] = 0x10325476;
 104
 105        /* Check to see if the seed is all zero's */
 106        if (hinfo->seed) {
 107                for (i=0; i < 4; i++) {
 108                        if (hinfo->seed[i])
 109                                break;
 110                }
 111                if (i < 4)
 112                        memcpy(buf, hinfo->seed, sizeof(buf));
 113        }
 114
 115        switch (hinfo->hash_version) {
 116        case DX_HASH_LEGACY:
 117                hash = dx_hack_hash(name, len);
 118                break;
 119        case DX_HASH_HALF_MD4:
 120                p = name;
 121                while (len > 0) {
 122                        str2hashbuf(p, len, in, 8);
 123                        half_md4_transform(buf, in);
 124                        len -= 32;
 125                        p += 32;
 126                }
 127                minor_hash = buf[2];
 128                hash = buf[1];
 129                break;
 130        case DX_HASH_TEA:
 131                p = name;
 132                while (len > 0) {
 133                        str2hashbuf(p, len, in, 4);
 134                        TEA_transform(buf, in);
 135                        len -= 16;
 136                        p += 16;
 137                }
 138                hash = buf[0];
 139                minor_hash = buf[1];
 140                break;
 141        default:
 142                hinfo->hash = 0;
 143                return -1;
 144        }
 145        hash = hash & ~1;
 146        if (hash == (EXT3_HTREE_EOF << 1))
 147                hash = (EXT3_HTREE_EOF-1) << 1;
 148        hinfo->hash = hash;
 149        hinfo->minor_hash = minor_hash;
 150        return 0;
 151}
 152