Infrastructure: Strip away crufty CVS $Id$ tags.

[mLib] / unihash.c

/* -*-c-*-
 *
 * Simple and efficient universal hashing for hashtables
 *
 * (c) 2003 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * mLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with mLib; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Header files ------------------------------------------------------*/

#include <assert.h>
#include <stdlib.h>

#include "unihash.h"

/*----- Main code ---------------------------------------------------------*/

/* --- @unihash_setkey@ --- *
 *
 * Arguments:   @unihash_info *i@ = where to store the precomputed tables
 *              @uint32 k@ = the key to set, randomly chosen
 *
 * Returns:     ---
 *
 * Use:         Calculates the tables required for efficient hashing.
 */

static uint32 mul(uint32 x, uint32 y)
{
  uint32 z = 0;
  while (y) {
    if (y & 1) z ^= x;
    if (x & (1 << 31))
      x = U32(x << 1) ^ UNIHASH_POLY;
    else
      x = U32(x << 1);
    y = U32(y >> 1);
  }
  return (z);
}

void unihash_setkey(unihash_info *i, uint32 k)
{
  size_t a;
  size_t b;
  uint32 x = 1;

  for (a = 0; a < UNIHASH_NBATCH; a++) {
    x = mul(x, k);
    for (b = 0; b < 256; b++) {
      i->s[a][0][b] = mul(x, b <<  0);
      i->s[a][1][b] = mul(x, b <<  8);
      i->s[a][2][b] = mul(x, b << 16);
      i->s[a][3][b] = mul(x, b << 24);
    }
  }
}

/* --- @unihash_hash@ --- *
 *
 * Arguments:   @const unihash_info *i@ = pointer to precomputed table
 *              @uint32 a@ = @i->[0][0][1]@ or value from previous call
 *              @const void *p@ = pointer to data to hash
 *              @size_t sz@ = size of the data
 *
 * Returns:     Hash of data so far.
 *
 * Use:         Hashes data.  Call this as many times as needed.
 */

uint32 unihash_hash(const unihash_info *i, uint32 a,
                    const void *p, size_t sz)
{
  const octet *pp = p;

  assert(UNIHASH_NBATCH == 4);

#define FULLMULT(u, x)                                                  \
  (i->s[u][0][U8((x) >>  0)] ^ i->s[u][1][U8((x) >>  8)] ^              \
   i->s[u][2][U8((x) >> 16)] ^ i->s[u][3][U8((x) >> 24)]);

#define BYTEMULT(u, x) i->s[u][0][x]

  /* --- Do the main bulk in batches of %$n$% bytes --- *
   *
   * We have %$a$% and %$m_{n-1}, \ldots, m_1, m_0$%; we want
   *
   * %$a' = (a + m_{n-1}) k^n + m_{n-2} k^{n-1} + \cdots + m_1 k^2 + m_0 k$%
   */

  while (sz >= UNIHASH_NBATCH) {
    a ^= *pp++;
    a = FULLMULT(3, a);
    a ^= BYTEMULT(2, *pp++);
    a ^= BYTEMULT(1, *pp++);
    a ^= BYTEMULT(0, *pp++);
    sz -= UNIHASH_NBATCH;
  }

  /* --- The tail end is a smaller batch --- */

  switch (sz) {
    case  3: a ^= *pp++; a = FULLMULT(2, a); goto batch_2;
    case  2: a ^= *pp++; a = FULLMULT(1, a); goto batch_1;
    case  1: a ^= *pp++; a = FULLMULT(0, a); goto batch_0;
    batch_2: a ^= BYTEMULT(1, *pp++);
    batch_1: a ^= BYTEMULT(0, *pp++);
    batch_0: break;
  }

  return (a);
}

/* --- @unihash@ --- *
 *
 * Arguments:   @const unihash_info *i@ = precomputed tables
 *              @const void *p@ = pointer to data to hash
 *              @size_t sz@ = size of the data
 *
 * Returns:     The hash value computed.
 *
 * Use:         All-in-one hashing function.  No faster than using the
 *              separate calls, but more convenient.
 */

uint32 unihash(const unihash_info *i, const void *p, size_t sz)
{
  return (UNIHASH(i, p, sz));
}

/*----- Test rig ----------------------------------------------------------*/

#ifdef TEST_RIG

#include "testrig.h"

static int verify(dstr *v)
{
  unihash_info ui;
  uint32 k;
  uint32 h, hh;
  size_t n;
  int i, c;
  const char *p;
  int ok = 1;

  static const int step[] = { 0, 1, 5, 6, 7, 8, 23, -1 };

  /* --- Set up for using this key --- */

  k = *(uint32 *)v[0].buf;
  h = *(uint32 *)v[2].buf;
  unihash_setkey(&ui, k);

  /* --- Hash the data a lot --- */

  for (i = 0; step[i] >= 0; i++) {
    c = step[i];
    if (!c)
      hh = unihash(&ui, v[1].buf, v[1].len);
    else {
      hh = UNIHASH_INIT(&ui);
      p = v[1].buf;
      n = v[1].len;
      while (n) {
        if (c > n) c = n;
        hh = unihash_hash(&ui, hh, p, c);
        p += c;
        n -= c;
      }
    }
    if (h != hh) {
      ok = 0;
      fprintf(stderr, "\nunihash failed\n");
      fprintf(stderr, "  key = %08lx\n", (unsigned long)k);
      fprintf(stderr, "  data = %s\n", v[1].buf);
      fprintf(stderr, "  step = %d\n", step[i]);
      fprintf(stderr, "  expected = %08lx\n", (unsigned long)h);
      fprintf(stderr, "  computed = %08lx\n", (unsigned long)hh);
    }
  }
  return (ok);
}

static const test_chunk tests[] = {
  { "hash", verify, { &type_uint32, &type_string, &type_uint32 } },
  { 0, 0, { 0 } }
};

int main(int argc, char *argv[])
{
  test_run(argc, argv, tests, "unihash.in");
  return (0);
}

#endif

/*----- That's all, folks -------------------------------------------------*/