hashes.c

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/*
 * 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 <[email protected]> 1998
 *
 * Jeremy has agreed to the contents of reiserfs/README. -Hans
 * Yura's function is added (04/07/2000)
 */

//
// keyed_hash
// yura_hash
// r5_hash
//

#include <linux/kernel.h>
#include "reiserfs.h"
#include <asm/types.h>

#define DELTA 0x9E3779B9
#define FULLROUNDS 10       /* 32 is overkill, 16 is strong crypto */
#define PARTROUNDS 6        /* 6 gets complete mixing */

/* a, b, c, d - data; h0, h1 - accumulated hash */
#define TEACORE(rounds)                         \
    do {                                \
        u32 sum = 0;                        \
        int n = rounds;                     \
        u32 b0, b1;                     \
                                    \
        b0 = h0;                        \
        b1 = h1;                        \
                                    \
        do                          \
        {                           \
            sum += DELTA;                   \
            b0 += ((b1 << 4)+a) ^ (b1+sum) ^ ((b1 >> 5)+b); \
            b1 += ((b0 << 4)+c) ^ (b0+sum) ^ ((b0 >> 5)+d); \
        } while(--n);                       \
                                    \
        h0 += b0;                       \
        h1 += b1;                       \
    } while(0)

u32 keyed_hash(const signed char *msg, int len)
{
    u32 k[] = { 0x9464a485, 0x542e1a94, 0x3e846bff, 0xb75bcfc3 };

    u32 h0 = k[0], h1 = k[1];
    u32 a, b, c, d;
    u32 pad;
    int i;

    //      assert(len >= 0 && len < 256);

    pad = (u32) len | ((u32) len << 8);
    pad |= pad << 16;

    while (len >= 16) {
        a = (u32) msg[0] |
            (u32) msg[1] << 8 | (u32) msg[2] << 16 | (u32) msg[3] << 24;
        b = (u32) msg[4] |
            (u32) msg[5] << 8 | (u32) msg[6] << 16 | (u32) msg[7] << 24;
        c = (u32) msg[8] |
            (u32) msg[9] << 8 |
            (u32) msg[10] << 16 | (u32) msg[11] << 24;
        d = (u32) msg[12] |
            (u32) msg[13] << 8 |
            (u32) msg[14] << 16 | (u32) msg[15] << 24;

        TEACORE(PARTROUNDS);

        len -= 16;
        msg += 16;
    }

    if (len >= 12) {
        a = (u32) msg[0] |
            (u32) msg[1] << 8 | (u32) msg[2] << 16 | (u32) msg[3] << 24;
        b = (u32) msg[4] |
            (u32) msg[5] << 8 | (u32) msg[6] << 16 | (u32) msg[7] << 24;
        c = (u32) msg[8] |
            (u32) msg[9] << 8 |
            (u32) msg[10] << 16 | (u32) msg[11] << 24;

        d = pad;
        for (i = 12; i < len; i++) {
            d <<= 8;
            d |= msg[i];
        }
    } else if (len >= 8) {
        a = (u32) msg[0] |
            (u32) msg[1] << 8 | (u32) msg[2] << 16 | (u32) msg[3] << 24;
        b = (u32) msg[4] |
            (u32) msg[5] << 8 | (u32) msg[6] << 16 | (u32) msg[7] << 24;

        c = d = pad;
        for (i = 8; i < len; i++) {
            c <<= 8;
            c |= msg[i];
        }
    } else if (len >= 4) {
        a = (u32) msg[0] |
            (u32) msg[1] << 8 | (u32) msg[2] << 16 | (u32) msg[3] << 24;

        b = c = d = pad;
        for (i = 4; i < len; i++) {
            b <<= 8;
            b |= msg[i];
        }
    } else {
        a = b = c = d = pad;
        for (i = 0; i < len; i++) {
            a <<= 8;
            a |= msg[i];
        }
    }

    TEACORE(FULLROUNDS);

/*  return 0;*/
    return h0 ^ h1;
}

/* What follows in this file is copyright 2000 by Hans Reiser, and the
 * licensing of what follows is governed by reiserfs/README */

u32 yura_hash(const signed char *msg, int len)
{
    int j, pow;
    u32 a, c;
    int i;

    for (pow = 1, i = 1; i < len; i++)
        pow = pow * 10;

    if (len == 1)
        a = msg[0] - 48;
    else
        a = (msg[0] - 48) * pow;

    for (i = 1; i < len; i++) {
        c = msg[i] - 48;
        for (pow = 1, j = i; j < len - 1; j++)
            pow = pow * 10;
        a = a + c * pow;
    }

    for (; i < 40; i++) {
        c = '0' - 48;
        for (pow = 1, j = i; j < len - 1; j++)
            pow = pow * 10;
        a = a + c * pow;
    }

    for (; i < 256; i++) {
        c = i;
        for (pow = 1, j = i; j < len - 1; j++)
            pow = pow * 10;
        a = a + c * pow;
    }

    a = a << 7;
    return a;
}

u32 r5_hash(const signed char *msg, int len)
{
    u32 a = 0;
    while (*msg) {
        a += *msg << 4;
        a += *msg >> 4;
        a *= 11;
        msg++;
    }
    return a;
}