| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: mpmul.c,v 1.1 2000/07/01 11:21:39 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 1.1 2000/07/01 11:21:39 mdw |
| 34 | * New interface for computing products of many (small) integers. |
| 35 | * |
| 36 | */ |
| 37 | |
| 38 | /*----- Header files ------------------------------------------------------*/ |
| 39 | |
| 40 | #include "mp.h" |
| 41 | #include "mpint.h" |
| 42 | #include "mpmul.h" |
| 43 | |
| 44 | /*----- Main code ---------------------------------------------------------*/ |
| 45 | |
| 46 | /* --- @mpmul_init@ --- * |
| 47 | * |
| 48 | * Arguments: @mpmul *b@ = pointer to multiplier context to initialize |
| 49 | * |
| 50 | * Returns: --- |
| 51 | * |
| 52 | * Use: Initializes a big multiplier context for use. |
| 53 | */ |
| 54 | |
| 55 | void mpmul_init(mpmul *b) |
| 56 | { |
| 57 | b->i = 0; |
| 58 | } |
| 59 | |
| 60 | /* --- @mpmul_add@ --- * |
| 61 | * |
| 62 | * Arguments: @mpmul *b@ = pointer to multiplier context |
| 63 | * @mp *x@ = the next factor to multiply in |
| 64 | * |
| 65 | * Returns: --- |
| 66 | * |
| 67 | * Use: Contributes another factor to the mix. It's important that |
| 68 | * the integer lasts at least as long as the multiplication |
| 69 | * context; this sort of rules out @mp_build@ integers. |
| 70 | */ |
| 71 | |
| 72 | void mpmul_add(mpmul *b, mp *x) |
| 73 | { |
| 74 | size_t i = b->i; |
| 75 | |
| 76 | /* --- Now do the reduction step --- */ |
| 77 | |
| 78 | x = MP_COPY(x); |
| 79 | |
| 80 | while (i > 0) { |
| 81 | if (MP_LEN(b->v[i - 1]) > MP_LEN(x)) |
| 82 | break; |
| 83 | i--; |
| 84 | x = mp_mul(x, x, b->v[i]); |
| 85 | MP_DROP(b->v[i]); |
| 86 | } |
| 87 | |
| 88 | if (i > HWM) { |
| 89 | while (i > LWM) { |
| 90 | i--; |
| 91 | x = mp_mul(x, x, b->v[i]); |
| 92 | MP_DROP(b->v[i]); |
| 93 | } |
| 94 | } |
| 95 | |
| 96 | b->v[i] = x; |
| 97 | b->i = i; |
| 98 | } |
| 99 | |
| 100 | /* --- @mpmul_done@ --- * |
| 101 | * |
| 102 | * Arguments: @mpmul *b@ = pointer to big multiplication context |
| 103 | * |
| 104 | * Returns: The product of all the numbers contributed. |
| 105 | * |
| 106 | * Use: Returns a (large) product of numbers. The context is |
| 107 | * deallocated. |
| 108 | */ |
| 109 | |
| 110 | mp *mpmul_done(mpmul *b) |
| 111 | { |
| 112 | size_t i = b->i; |
| 113 | mp *x; |
| 114 | |
| 115 | if (!i) |
| 116 | return (MP_ONE); |
| 117 | i--; |
| 118 | x = b->v[i]; |
| 119 | while (i > 0) { |
| 120 | i--; |
| 121 | x = mp_mul(x, x, b->v[i]); |
| 122 | MP_DROP(b->v[i]); |
| 123 | } |
| 124 | return (x); |
| 125 | } |
| 126 | |
| 127 | /* --- @mp_factorial@ --- * |
| 128 | * |
| 129 | * Arguments: @unsigned long i@ = number whose factorial should be |
| 130 | * computed. |
| 131 | * |
| 132 | * Returns: The requested factorial. |
| 133 | */ |
| 134 | |
| 135 | mp *mp_factorial(unsigned long i) |
| 136 | { |
| 137 | unsigned long j; |
| 138 | mp *x = MP_NEW; |
| 139 | mpmul b = MPMUL_INIT; |
| 140 | |
| 141 | for (j = 1; j <= i; j++) { |
| 142 | x = mp_fromulong(x, j); |
| 143 | mpmul_add(&b, x); |
| 144 | } |
| 145 | mp_drop(x); |
| 146 | return (mpmul_done(&b)); |
| 147 | } |
| 148 | |
| 149 | /*----- That's all, folks -------------------------------------------------*/ |