git.distorted.org.uk Git - u/mdw/catacomb/blob - mpmul.c

   1 /* -*-c-*-
   2  *
   3  * $Id: mpmul.c,v 1.4 2001/02/03 12:00:29 mdw Exp $
   4  *
   5  * Multiply many small numbers together
   6  *
   7  * (c) 2000 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: mpmul.c,v $
  33  * Revision 1.4  2001/02/03 12:00:29  mdw
  34  * Now @mp_drop@ checks its argument is non-NULL before attempting to free
  35  * it.  Note that the macro version @MP_DROP@ doesn't do this.
  36  *
  37  * Revision 1.3  2000/10/08 12:11:22  mdw
  38  * Use @MP_EQ@ instead of @MP_CMP@.
  39  *
  40  * Revision 1.2  2000/07/09 21:31:10  mdw
  41  * Fix bug, and add a test rig.
  42  *
  43  * Revision 1.1  2000/07/01 11:21:39  mdw
  44  * New interface for computing products of many (small) integers.
  45  *
  46  */
  47
  48 /*----- Header files ------------------------------------------------------*/
  49
  50 #include "mp.h"
  51 #include "mpint.h"
  52 #include "mpmul.h"
  53
  54 /*----- Main code ---------------------------------------------------------*/
  55
  56 /* --- @mpmul_init@ --- *
  57  *
  58  * Arguments:   @mpmul *b@ = pointer to multiplier context to initialize
  59  *
  60  * Returns:     ---
  61  *
  62  * Use:         Initializes a big multiplier context for use.
  63  */
  64
  65 void mpmul_init(mpmul *b)
  66 {
  67   b->i = 0;
  68 }
  69
  70 /* --- @mpmul_add@ --- *
  71  *
  72  * Arguments:   @mpmul *b@ = pointer to multiplier context
  73  *              @mp *x@ = the next factor to multiply in
  74  *
  75  * Returns:     ---
  76  *
  77  * Use:         Contributes another factor to the mix.  It's important that
  78  *              the integer lasts at least as long as the multiplication
  79  *              context; this sort of rules out @mp_build@ integers.
  80  */
  81
  82 void mpmul_add(mpmul *b, mp *x)
  83 {
  84   size_t i = b->i;
  85
  86   /* --- Now do the reduction step --- */
  87
  88   x = MP_COPY(x);
  89
  90   while (i > 0) {
  91     if (MP_LEN(b->v[i - 1]) > MP_LEN(x))
  92       break;
  93     i--;
  94     x = mp_mul(x, x, b->v[i]);
  95     MP_DROP(b->v[i]);
  96   }
  97
  98   if (i > HWM) {
  99     while (i > LWM || (i > 0 && MP_LEN(b->v[i - 1]) <= MP_LEN(x))) {
 100       i--;
 101       x = mp_mul(x, x, b->v[i]);
 102       MP_DROP(b->v[i]);
 103     }
 104   }
 105
 106   b->v[i++] = x;
 107   b->i = i;
 108 }
 109
 110 /* --- @mpmul_done@ --- *
 111  *
 112  * Arguments:   @mpmul *b@ = pointer to big multiplication context
 113  *
 114  * Returns:     The product of all the numbers contributed.
 115  *
 116  * Use:         Returns a (large) product of numbers.  The context is
 117  *              deallocated.
 118  */
 119
 120 mp *mpmul_done(mpmul *b)
 121 {
 122   size_t i = b->i;
 123   mp *x;
 124
 125   if (!i)
 126     return (MP_ONE);
 127   i--;
 128   x = b->v[i];
 129   while (i > 0) {
 130     i--;
 131     x = mp_mul(x, x, b->v[i]);
 132     MP_DROP(b->v[i]);
 133   }
 134   return (x);
 135 }
 136
 137 /* --- @mp_factorial@ --- *
 138  *
 139  * Arguments:   @unsigned long i@ = number whose factorial should be
 140  *                      computed.
 141  *
 142  * Returns:     The requested factorial.
 143  */
 144
 145 mp *mp_factorial(unsigned long i)
 146 {
 147   unsigned long j;
 148   mp *x = MP_NEW;
 149   mpmul b = MPMUL_INIT;
 150
 151   for (j = 1; j <= i; j++) {
 152     x = mp_fromulong(x, j);
 153     mpmul_add(&b, x);
 154   }
 155   mp_drop(x);
 156   return (mpmul_done(&b));
 157 }
 158
 159 /*----- Test rig ----------------------------------------------------------*/
 160
 161 #ifdef TEST_RIG
 162
 163 #include <mLib/testrig.h>
 164
 165 static int vfact(dstr *v)
 166 {
 167   unsigned long x = *(unsigned long *)v[0].buf;
 168   mp *fx = *(mp **)v[1].buf;
 169   mp *y = mp_factorial(x);
 170   int ok = 1;
 171   if (!MP_EQ(fx, y)) {
 172     fprintf(stderr, "factorial failed\n");
 173     MP_FPRINTF(stderr, (stderr, "%lu! = ", x), fx);
 174     MP_EPRINT("result", y);
 175     ok = 0;
 176   }
 177   mp_drop(fx);
 178   mp_drop(y);
 179   assert(mparena_count(MPARENA_GLOBAL) == 0);
 180   return (ok);
 181 }
 182
 183 static test_chunk tests[] = {
 184   { "factorial", vfact, { &type_ulong, &type_mp, 0 } },
 185   { 0, 0, { 0 } }
 186 };
 187
 188 int main(int argc, char *argv[])
 189 {
 190   test_run(argc, argv, tests, SRCDIR "/tests/mp");
 191   return (0);
 192 }
 193
 194 #endif
 195
 196 /*----- That's all, folks -------------------------------------------------*/