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/compiler.h>
  14 #include <linux/bitops.h>
  15 #include "ext4.h"
  16
  17 #define DELTA 0x9E3779B9
  18
  19 static 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 /* F, G and H are basic MD4 functions: selection, majority, parity */
  37 #define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
  38 #define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
  39 #define H(x, y, z) ((x) ^ (y) ^ (z))
  40
  41 /*
  42  * The generic round function.  The application is so specific that
  43  * we don't bother protecting all the arguments with parens, as is generally
  44  * good macro practice, in favor of extra legibility.
  45  * Rotation is separate from addition to prevent recomputation
  46  */
  47 #define ROUND(f, a, b, c, d, x, s)      \
  48         (a += f(b, c, d) + x, a = rol32(a, s))
  49 #define K1 0
  50 #define K2 013240474631UL
  51 #define K3 015666365641UL
  52
  53 /*
  54  * Basic cut-down MD4 transform.  Returns only 32 bits of result.
  55  */
  56 static __u32 half_md4_transform(__u32 buf[4], __u32 const in[8])
  57 {
  58         __u32 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
  59
  60         /* Round 1 */
  61         ROUND(F, a, b, c, d, in[0] + K1,  3);
  62         ROUND(F, d, a, b, c, in[1] + K1,  7);
  63         ROUND(F, c, d, a, b, in[2] + K1, 11);
  64         ROUND(F, b, c, d, a, in[3] + K1, 19);
  65         ROUND(F, a, b, c, d, in[4] + K1,  3);
  66         ROUND(F, d, a, b, c, in[5] + K1,  7);
  67         ROUND(F, c, d, a, b, in[6] + K1, 11);
  68         ROUND(F, b, c, d, a, in[7] + K1, 19);
  69
  70         /* Round 2 */
  71         ROUND(G, a, b, c, d, in[1] + K2,  3);
  72         ROUND(G, d, a, b, c, in[3] + K2,  5);
  73         ROUND(G, c, d, a, b, in[5] + K2,  9);
  74         ROUND(G, b, c, d, a, in[7] + K2, 13);
  75         ROUND(G, a, b, c, d, in[0] + K2,  3);
  76         ROUND(G, d, a, b, c, in[2] + K2,  5);
  77         ROUND(G, c, d, a, b, in[4] + K2,  9);
  78         ROUND(G, b, c, d, a, in[6] + K2, 13);
  79
  80         /* Round 3 */
  81         ROUND(H, a, b, c, d, in[3] + K3,  3);
  82         ROUND(H, d, a, b, c, in[7] + K3,  9);
  83         ROUND(H, c, d, a, b, in[2] + K3, 11);
  84         ROUND(H, b, c, d, a, in[6] + K3, 15);
  85         ROUND(H, a, b, c, d, in[1] + K3,  3);
  86         ROUND(H, d, a, b, c, in[5] + K3,  9);
  87         ROUND(H, c, d, a, b, in[0] + K3, 11);
  88         ROUND(H, b, c, d, a, in[4] + K3, 15);
  89
  90         buf[0] += a;
  91         buf[1] += b;
  92         buf[2] += c;
  93         buf[3] += d;
  94
  95         return buf[1]; /* "most hashed" word */
  96 }
  97 #undef ROUND
  98 #undef K1
  99 #undef K2
 100 #undef K3
 101 #undef F
 102 #undef G
 103 #undef H
 104
 105 /* The old legacy hash */
 106 static __u32 dx_hack_hash_unsigned(const char *name, int len)
 107 {
 108         __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
 109         const unsigned char *ucp = (const unsigned char *) name;
 110
 111         while (len--) {
 112                 hash = hash1 + (hash0 ^ (((int) *ucp++) * 7152373));
 113
 114                 if (hash & 0x80000000)
 115                         hash -= 0x7fffffff;
 116                 hash1 = hash0;
 117                 hash0 = hash;
 118         }
 119         return hash0 << 1;
 120 }
 121
 122 static __u32 dx_hack_hash_signed(const char *name, int len)
 123 {
 124         __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
 125         const signed char *scp = (const signed char *) name;
 126
 127         while (len--) {
 128                 hash = hash1 + (hash0 ^ (((int) *scp++) * 7152373));
 129
 130                 if (hash & 0x80000000)
 131                         hash -= 0x7fffffff;
 132                 hash1 = hash0;
 133                 hash0 = hash;
 134         }
 135         return hash0 << 1;
 136 }
 137
 138 static void str2hashbuf_signed(const char *msg, int len, __u32 *buf, int num)
 139 {
 140         __u32   pad, val;
 141         int     i;
 142         const signed char *scp = (const signed char *) msg;
 143
 144         pad = (__u32)len | ((__u32)len << 8);
 145         pad |= pad << 16;
 146
 147         val = pad;
 148         if (len > num*4)
 149                 len = num * 4;
 150         for (i = 0; i < len; i++) {
 151                 val = ((int) scp[i]) + (val << 8);
 152                 if ((i % 4) == 3) {
 153                         *buf++ = val;
 154                         val = pad;
 155                         num--;
 156                 }
 157         }
 158         if (--num >= 0)
 159                 *buf++ = val;
 160         while (--num >= 0)
 161                 *buf++ = pad;
 162 }
 163
 164 static void str2hashbuf_unsigned(const char *msg, int len, __u32 *buf, int num)
 165 {
 166         __u32   pad, val;
 167         int     i;
 168         const unsigned char *ucp = (const unsigned char *) msg;
 169
 170         pad = (__u32)len | ((__u32)len << 8);
 171         pad |= pad << 16;
 172
 173         val = pad;
 174         if (len > num*4)
 175                 len = num * 4;
 176         for (i = 0; i < len; i++) {
 177                 val = ((int) ucp[i]) + (val << 8);
 178                 if ((i % 4) == 3) {
 179                         *buf++ = val;
 180                         val = pad;
 181                         num--;
 182                 }
 183         }
 184         if (--num >= 0)
 185                 *buf++ = val;
 186         while (--num >= 0)
 187                 *buf++ = pad;
 188 }
 189
 190 /*
 191  * Returns the hash of a filename.  If len is 0 and name is NULL, then
 192  * this function can be used to test whether or not a hash version is
 193  * supported.
 194  *
 195  * The seed is an 4 longword (32 bits) "secret" which can be used to
 196  * uniquify a hash.  If the seed is all zero's, then some default seed
 197  * may be used.
 198  *
 199  * A particular hash version specifies whether or not the seed is
 200  * represented, and whether or not the returned hash is 32 bits or 64
 201  * bits.  32 bit hashes will return 0 for the minor hash.
 202  */
 203 int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
 204 {
 205         __u32   hash;
 206         __u32   minor_hash = 0;
 207         const char      *p;
 208         int             i;
 209         __u32           in[8], buf[4];
 210         void            (*str2hashbuf)(const char *, int, __u32 *, int) =
 211                                 str2hashbuf_signed;
 212
 213         /* Initialize the default seed for the hash checksum functions */
 214         buf[0] = 0x67452301;
 215         buf[1] = 0xefcdab89;
 216         buf[2] = 0x98badcfe;
 217         buf[3] = 0x10325476;
 218
 219         /* Check to see if the seed is all zero's */
 220         if (hinfo->seed) {
 221                 for (i = 0; i < 4; i++) {
 222                         if (hinfo->seed[i]) {
 223                                 memcpy(buf, hinfo->seed, sizeof(buf));
 224                                 break;
 225                         }
 226                 }
 227         }
 228
 229         switch (hinfo->hash_version) {
 230         case DX_HASH_LEGACY_UNSIGNED:
 231                 hash = dx_hack_hash_unsigned(name, len);
 232                 break;
 233         case DX_HASH_LEGACY:
 234                 hash = dx_hack_hash_signed(name, len);
 235                 break;
 236         case DX_HASH_HALF_MD4_UNSIGNED:
 237                 str2hashbuf = str2hashbuf_unsigned;
 238         case DX_HASH_HALF_MD4:
 239                 p = name;
 240                 while (len > 0) {
 241                         (*str2hashbuf)(p, len, in, 8);
 242                         half_md4_transform(buf, in);
 243                         len -= 32;
 244                         p += 32;
 245                 }
 246                 minor_hash = buf[2];
 247                 hash = buf[1];
 248                 break;
 249         case DX_HASH_TEA_UNSIGNED:
 250                 str2hashbuf = str2hashbuf_unsigned;
 251         case DX_HASH_TEA:
 252                 p = name;
 253                 while (len > 0) {
 254                         (*str2hashbuf)(p, len, in, 4);
 255                         TEA_transform(buf, in);
 256                         len -= 16;
 257                         p += 16;
 258                 }
 259                 hash = buf[0];
 260                 minor_hash = buf[1];
 261                 break;
 262         default:
 263                 hinfo->hash = 0;
 264                 return -1;
 265         }
 266         hash = hash & ~1;
 267         if (hash == (EXT4_HTREE_EOF_32BIT << 1))
 268                 hash = (EXT4_HTREE_EOF_32BIT - 1) << 1;
 269         hinfo->hash = hash;
 270         hinfo->minor_hash = minor_hash;
 271         return 0;
 272 }