source: MondoRescue/branches/stable/mindi-busybox/e2fsprogs/ext2fs/dirhash.c@ 821

/*
 * dirhash.c -- Calculate the hash of a directory entry
 *
 * Copyright (c) 2001  Daniel Phillips
 *
 * Copyright (c) 2002 Theodore Ts'o.
 *
 * %Begin-Header%
 * This file may be redistributed under the terms of the GNU Public
 * License.
 * %End-Header%
 */

#include <stdio.h>
#include <string.h>

#include "ext2_fs.h"
#include "ext2fs.h"

/*
 * Keyed 32-bit hash function using TEA in a Davis-Meyer function
 *   H0 = Key
 *   Hi = E Mi(Hi-1) + Hi-1
 *
 * (see Applied Cryptography, 2nd edition, p448).
 *
 * Jeremy Fitzhardinge <jeremy@zip.com.au> 1998
 *
 * This code is made available under the terms of the GPL
 */
#define DELTA 0x9E3779B9

static void TEA_transform(__u32 buf[4], __u32 const in[])
{
    __u32   sum = 0;
    __u32   b0 = buf[0], b1 = buf[1];
    __u32   a = in[0], b = in[1], c = in[2], d = in[3];
    int n = 16;

    do {
        sum += DELTA;
        b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b);
        b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d);
    } while(--n);

    buf[0] += b0;
    buf[1] += b1;
}

/* F, G and H are basic MD4 functions: selection, majority, parity */
#define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))
#define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))

/*
 * The generic round function.  The application is so specific that
 * we don't bother protecting all the arguments with parens, as is generally
 * good macro practice, in favor of extra legibility.
 * Rotation is separate from addition to prevent recomputation
 */
#define ROUND(f, a, b, c, d, x, s)  \
    (a += f(b, c, d) + x, a = (a << s) | (a >> (32-s)))
#define K1 0
#define K2 013240474631UL
#define K3 015666365641UL

/*
 * Basic cut-down MD4 transform.  Returns only 32 bits of result.
 */
static void halfMD4Transform (__u32 buf[4], __u32 const in[])
{
    __u32   a = buf[0], b = buf[1], c = buf[2], d = buf[3];

    /* Round 1 */
    ROUND(F, a, b, c, d, in[0] + K1,  3);
    ROUND(F, d, a, b, c, in[1] + K1,  7);
    ROUND(F, c, d, a, b, in[2] + K1, 11);
    ROUND(F, b, c, d, a, in[3] + K1, 19);
    ROUND(F, a, b, c, d, in[4] + K1,  3);
    ROUND(F, d, a, b, c, in[5] + K1,  7);
    ROUND(F, c, d, a, b, in[6] + K1, 11);
    ROUND(F, b, c, d, a, in[7] + K1, 19);

    /* Round 2 */
    ROUND(G, a, b, c, d, in[1] + K2,  3);
    ROUND(G, d, a, b, c, in[3] + K2,  5);
    ROUND(G, c, d, a, b, in[5] + K2,  9);
    ROUND(G, b, c, d, a, in[7] + K2, 13);
    ROUND(G, a, b, c, d, in[0] + K2,  3);
    ROUND(G, d, a, b, c, in[2] + K2,  5);
    ROUND(G, c, d, a, b, in[4] + K2,  9);
    ROUND(G, b, c, d, a, in[6] + K2, 13);

    /* Round 3 */
    ROUND(H, a, b, c, d, in[3] + K3,  3);
    ROUND(H, d, a, b, c, in[7] + K3,  9);
    ROUND(H, c, d, a, b, in[2] + K3, 11);
    ROUND(H, b, c, d, a, in[6] + K3, 15);
    ROUND(H, a, b, c, d, in[1] + K3,  3);
    ROUND(H, d, a, b, c, in[5] + K3,  9);
    ROUND(H, c, d, a, b, in[0] + K3, 11);
    ROUND(H, b, c, d, a, in[4] + K3, 15);

    buf[0] += a;
    buf[1] += b;
    buf[2] += c;
    buf[3] += d;
}

#undef ROUND
#undef F
#undef G
#undef H
#undef K1
#undef K2
#undef K3

/* The old legacy hash */
static ext2_dirhash_t dx_hack_hash (const char *name, int len)
{
    __u32 hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
    while (len--) {
        __u32 hash = hash1 + (hash0 ^ (*name++ * 7152373));

        if (hash & 0x80000000) hash -= 0x7fffffff;
        hash1 = hash0;
        hash0 = hash;
    }
    return (hash0 << 1);
}

static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
{
    __u32   pad, val;
    int i;

    pad = (__u32)len | ((__u32)len << 8);
    pad |= pad << 16;

    val = pad;
    if (len > num*4)
        len = num * 4;
    for (i=0; i < len; i++) {
        if ((i % 4) == 0)
            val = pad;
        val = msg[i] + (val << 8);
        if ((i % 4) == 3) {
            *buf++ = val;
            val = pad;
            num--;
        }
    }
    if (--num >= 0)
        *buf++ = val;
    while (--num >= 0)
        *buf++ = pad;
}

/*
 * Returns the hash of a filename.  If len is 0 and name is NULL, then
 * this function can be used to test whether or not a hash version is
 * supported.
 *
 * The seed is an 4 longword (32 bits) "secret" which can be used to
 * uniquify a hash.  If the seed is all zero's, then some default seed
 * may be used.
 *
 * A particular hash version specifies whether or not the seed is
 * represented, and whether or not the returned hash is 32 bits or 64
 * bits.  32 bit hashes will return 0 for the minor hash.
 */
errcode_t ext2fs_dirhash(int version, const char *name, int len,
             const __u32 *seed,
             ext2_dirhash_t *ret_hash,
             ext2_dirhash_t *ret_minor_hash)
{
    __u32   hash;
    __u32   minor_hash = 0;
    const char  *p;
    int     i;
    __u32       in[8], buf[4];

    /* Initialize the default seed for the hash checksum functions */
    buf[0] = 0x67452301;
    buf[1] = 0xefcdab89;
    buf[2] = 0x98badcfe;
    buf[3] = 0x10325476;

    /* Check to see if the seed is all zero's */
    if (seed) {
        for (i=0; i < 4; i++) {
            if (seed[i])
                break;
        }
        if (i < 4)
            memcpy(buf, seed, sizeof(buf));
    }

    switch (version) {
    case EXT2_HASH_LEGACY:
        hash = dx_hack_hash(name, len);
        break;
    case EXT2_HASH_HALF_MD4:
        p = name;
        while (len > 0) {
            str2hashbuf(p, len, in, 8);
            halfMD4Transform(buf, in);
            len -= 32;
            p += 32;
        }
        minor_hash = buf[2];
        hash = buf[1];
        break;
    case EXT2_HASH_TEA:
        p = name;
        while (len > 0) {
            str2hashbuf(p, len, in, 4);
            TEA_transform(buf, in);
            len -= 16;
            p += 16;
        }
        hash = buf[0];
        minor_hash = buf[1];
        break;
    default:
        *ret_hash = 0;
        return EXT2_ET_DIRHASH_UNSUPP;
    }
    *ret_hash = hash & ~1;
    if (ret_minor_hash)
        *ret_minor_hash = minor_hash;
    return 0;
}