hash.c

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/*
 *  linux/fs/ext4/hash.c
 *
 * Copyright (C) 2002 by Theodore Ts'o
 *
 * This file is released under the GPL v2.
 *
 * This file may be redistributed under the terms of the GNU Public
 * License.
 */

#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/cryptohash.h>
#include "ext4.h"

#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;
}


/* The old legacy hash */
static __u32 dx_hack_hash_unsigned(const char *name, int len)
{
    __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
    const unsigned char *ucp = (const unsigned char *) name;

    while (len--) {
        hash = hash1 + (hash0 ^ (((int) *ucp++) * 7152373));

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

static __u32 dx_hack_hash_signed(const char *name, int len)
{
    __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
    const signed char *scp = (const signed char *) name;

    while (len--) {
        hash = hash1 + (hash0 ^ (((int) *scp++) * 7152373));

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

static void str2hashbuf_signed(const char *msg, int len, __u32 *buf, int num)
{
    __u32   pad, val;
    int i;
    const signed char *scp = (const signed char *) msg;

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

static void str2hashbuf_unsigned(const char *msg, int len, __u32 *buf, int num)
{
    __u32   pad, val;
    int i;
    const unsigned char *ucp = (const unsigned char *) msg;

    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 = ((int) ucp[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.
 */
int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
{
    __u32   hash;
    __u32   minor_hash = 0;
    const char  *p;
    int     i;
    __u32       in[8], buf[4];
    void        (*str2hashbuf)(const char *, int, __u32 *, int) =
                str2hashbuf_signed;

    /* 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 (hinfo->seed) {
        for (i = 0; i < 4; i++) {
            if (hinfo->seed[i])
                break;
        }
        if (i < 4)
            memcpy(buf, hinfo->seed, sizeof(buf));
    }

    switch (hinfo->hash_version) {
    case DX_HASH_LEGACY_UNSIGNED:
        hash = dx_hack_hash_unsigned(name, len);
        break;
    case DX_HASH_LEGACY:
        hash = dx_hack_hash_signed(name, len);
        break;
    case DX_HASH_HALF_MD4_UNSIGNED:
        str2hashbuf = str2hashbuf_unsigned;
    case DX_HASH_HALF_MD4:
        p = name;
        while (len > 0) {
            (*str2hashbuf)(p, len, in, 8);
            half_md4_transform(buf, in);
            len -= 32;
            p += 32;
        }
        minor_hash = buf[2];
        hash = buf[1];
        break;
    case DX_HASH_TEA_UNSIGNED:
        str2hashbuf = str2hashbuf_unsigned;
    case DX_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:
        hinfo->hash = 0;
        return -1;
    }
    hash = hash & ~1;
    if (hash == (EXT4_HTREE_EOF_32BIT << 1))
        hash = (EXT4_HTREE_EOF_32BIT - 1) << 1;
    hinfo->hash = hash;
    hinfo->minor_hash = minor_hash;
    return 0;
}