Andrew's git - gitweb.git/blob

   1/*
   2 *
   3 * Copyright (C) 1999 David Mazieres (dm@uun.org)
   4 *
   5 * This program is free software; you can redistribute it and/or
   6 * modify it under the terms of the GNU General Public License as
   7 * published by the Free Software Foundation; either version 2, or (at
   8 * your option) any later version.
   9 *
  10 * This program is distributed in the hope that it will be useful, but
  11 * WITHOUT ANY WARRANTY; without even the implied warranty of
  12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 * General Public License for more details.
  14 *
  15 * You should have received a copy of the GNU General Public License
  16 * along with this program; if not, write to the Free Software
  17 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
  18 * USA
  19 *
  20 */
  21
  22  /* Faster generic_fls */
  23  /* (c) 2002, D.Phillips and Sistina Software */
  24
  25#include "rabinpoly.h"
  26#define MSB64 0x8000000000000000ULL
  27
  28static inline unsigned fls8(unsigned n)
  29{
  30       return n & 0xf0?
  31           n & 0xc0? (n >> 7) + 7: (n >> 5) + 5:
  32           n & 0x0c? (n >> 3) + 3: n - ((n + 1) >> 2);
  33}
  34
  35static inline unsigned fls16(unsigned n)
  36{
  37       return n & 0xff00? fls8(n >> 8) + 8: fls8(n);
  38}
  39
  40static inline unsigned fls32(unsigned n)
  41{
  42       return n & 0xffff0000? fls16(n >> 16) + 16: fls16(n);
  43}
  44
  45static inline unsigned fls64(unsigned long long n) /* should be u64 */
  46{
  47       return n & 0xffffffff00000000ULL? fls32(n >> 32) + 32: fls32(n);
  48}
  49
  50
  51static u_int64_t polymod (u_int64_t nh, u_int64_t nl, u_int64_t d);
  52static void      polymult (u_int64_t *php, u_int64_t *plp,
  53                           u_int64_t x, u_int64_t y);
  54static u_int64_t polymmult (u_int64_t x, u_int64_t y, u_int64_t d);
  55
  56static u_int64_t poly = 0xb15e234bd3792f63ull;  // Actual polynomial
  57static u_int64_t T[256];                        // Lookup table for mod
  58static int shift;
  59
  60u_int64_t append8 (u_int64_t p, u_char m)
  61{ return ((p << 8) | m) ^ T[p >> shift];
  62}
  63
  64static u_int64_t
  65polymod (u_int64_t nh, u_int64_t nl, u_int64_t d)
  66{ int i, k;
  67  assert (d);
  68  k = fls64 (d) - 1;
  69  d <<= 63 - k;
  70
  71  if (nh) {
  72    if (nh & MSB64)
  73      nh ^= d;
  74    for (i = 62; i >= 0; i--)
  75      if (nh & 1ULL << i) {
  76        nh ^= d >> (63 - i);
  77        nl ^= d << (i + 1);
  78      }
  79  }
  80  for (i = 63; i >= k; i--)
  81    if (nl & 1ULL << i)
  82      nl ^= d >> (63 - i);
  83  return nl;
  84}
  85
  86static void
  87polymult (u_int64_t *php, u_int64_t *plp, u_int64_t x, u_int64_t y)
  88{ int i;
  89  u_int64_t ph = 0, pl = 0;
  90  if (x & 1)
  91    pl = y;
  92  for (i = 1; i < 64; i++)
  93    if (x & (1ULL << i)) {
  94      ph ^= y >> (64 - i);
  95      pl ^= y << i;
  96    }
  97  if (php)
  98    *php = ph;
  99  if (plp)
 100    *plp = pl;
 101}
 102
 103static u_int64_t
 104polymmult (u_int64_t x, u_int64_t y, u_int64_t d)
 105{
 106  u_int64_t h, l;
 107  polymult (&h, &l, x, y);
 108  return polymod (h, l, d);
 109}
 110
 111static int size = RABIN_WINDOW_SIZE;
 112static u_int64_t fingerprint = 0;
 113static int bufpos = -1;
 114static u_int64_t U[256];
 115static u_char buf[RABIN_WINDOW_SIZE];
 116
 117void rabin_init ()
 118{ u_int64_t sizeshift = 1;
 119 u_int64_t T1;
 120  int xshift;
 121  int i, j;
 122  assert (poly >= 0x100);
 123  xshift = fls64 (poly) - 1;
 124  shift = xshift - 8;
 125  T1 = polymod (0, 1ULL << xshift, poly);
 126  for (j = 0; j < 256; j++)
 127    T[j] = polymmult (j, T1, poly) | ((u_int64_t) j << xshift);
 128
 129  for (i = 1; i < size; i++)
 130    sizeshift = append8 (sizeshift, 0);
 131  for (i = 0; i < 256; i++)
 132    U[i] = polymmult (i, sizeshift, poly);
 133  bzero (buf, sizeof (buf));
 134}
 135
 136void
 137rabin_reset ()
 138{ rabin_init();
 139  fingerprint = 0;
 140  bzero (buf, sizeof (buf));
 141}
 142
 143u_int64_t
 144rabin_slide8 (u_char m)
 145{ u_char om;
 146  if (++bufpos >= size) bufpos = 0;
 147
 148  om = buf[bufpos];
 149  buf[bufpos] = m;
 150  fingerprint = append8 (fingerprint ^ U[om], m);
 151
 152  return fingerprint;
 153}
 154