chiark - git - mdw - catacomb/blob - mpint.h

   1 /* -*-c-*-
   2  *
   3  * $Id: mpint.h,v 1.1 1999/11/25 11:38:31 mdw Exp $
   4  *
   5  * Conversion between MPs and standard C integers
   6  *
   7  * (c) 1999 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: mpint.h,v $
  33  * Revision 1.1  1999/11/25 11:38:31  mdw
  34  * Support for conversions between MPs and C integers.
  35  *
  36  */
  37
  38 #ifndef MPINT_H
  39 #define MPINT_H
  40
  41 #ifdef __cplusplus
  42   extern "C" {
  43 #endif
  44
  45 /*----- Header files ------------------------------------------------------*/
  46
  47 #include <limits.h>
  48
  49 #ifndef MP_H
  50 #  include "mp.h"
  51 #endif
  52
  53 /*----- Generic translation macros ----------------------------------------*/
  54
  55 /* --- @MP_FROMINT@ --- *
  56  *
  57  * Arguments:   @d@ = destination multiprecision integer
  58  *              @type@ = type of integer which @i@ is
  59  *              @i@ = a standard C integer
  60  *
  61  * Use:         Stores the value of @i@ in @d@.  This macro is actually
  62  *              rather subtle in places.  Be careful what you change.
  63  */
  64
  65 #define MP_FROMINT(d, type, i) do {                                     \
  66   type _i = (i);                                                        \
  67   size_t _o = 0;                                                        \
  68   mp *_d = (d);                                                         \
  69   size_t _sz = 4;                                                       \
  70                                                                         \
  71   MP_MODIFY(_d, _sz);                                                   \
  72   _d->f &= ~(MP_NEG | MP_UNDEF);                                        \
  73                                                                         \
  74   /* --- Set the sign on the MP --- *                                   \
  75    *                                                                    \
  76    * If the input integer is *not* negative, then negate it.  This      \
  77    * fixes a problem with two's complement machines where the most      \
  78    * negative value actually has larger magnitude than the most         \
  79    * positive, and hence -TYPE_MIN == TYPE_MIN but TYPE_MIN != 0.  If   \
  80    * all the work is carried out on negative numbers there isn't a      \
  81    * problem.                                                           \
  82    */                                                                   \
  83                                                                         \
  84   if (_i >= 0)                                                          \
  85     _i = -_i;                                                           \
  86   else                                                                  \
  87     _d->f |= MP_NEG;                                                    \
  88                                                                         \
  89   while (_i) {                                                          \
  90     if (_o == _sz) {                                                    \
  91       _sz <<= 1;                                                        \
  92       MP_ENSURE(_d, _sz);                                               \
  93     }                                                                   \
  94     _d->v[_o++] = MPW(-_i);                                             \
  95                                                                         \
  96     /* --- More subtlety --- *                                          \
  97      *                                                                  \
  98      * Ideally, I'd like to just shift @i@ right by @MPW_BITS@.  But I  \
  99      * can't, because that might be more than I'm allowed.  I can't     \
 100      * divide by @MPW_MAX + 1@ because that might turn out to be zero   \
 101      * in my current type, and besides which it's unsigned which messes \
 102      * up all of my negative arithmetic.  So do an explicit test here.  \
 103      */                                                                 \
 104                                                                         \
 105     if (_i > -MPW_MAX)                                                  \
 106       break;                                                            \
 107     else                                                                \
 108       _i /= (type)MPW_MAX + 1;                                          \
 109   }                                                                     \
 110   _d->vl = _d->v + _o;                                                  \
 111   (d) = _d;                                                             \
 112 } while (0)
 113
 114 /* --- @MP_TOINT@ --- *
 115  *
 116  * Arguments:   @m@ = a multiprecision integer
 117  *              @type@ = the type of @i@
 118  *              @max@ = the largest value @i@ can represent
 119  *              @i@ = an integer variable
 120  *
 121  * Use:         Stores the value of a multiprecision integer in a standard C
 122  *              integer.  If the value won't fit, the behaviour is determined
 123  *              by the type of @i@: if @i@ is unsigned, the value of the
 124  *              multiprecision integer modulo @max + 1@ is stored; if @i@ is
 125  *              signed, the behaviour is undefined.
 126  *
 127  *              If you don't want to be bitten by these sorts of things, keep
 128  *              copies of @INT_MAX@ or whatever is appropriate in
 129  *              multiprecision form and compare before conversion.
 130  */
 131
 132 #define MP_TOINT(m, type, max, i) do {                                  \
 133   type _i = 0;                                                          \
 134   type _max = (max);                                                    \
 135   unsigned _s = 0;                                                      \
 136   const mp *_m = (m);                                                   \
 137   const mpw *_v = _m->v, *_vl = _m->vl;                                 \
 138                                                                         \
 139   /* --- Do all the arithmetic in negative numbers --- */               \
 140                                                                         \
 141   while (_v < _vl && _max > 0) {                                        \
 142     _i -= *_v << _s;                                                    \
 143     _s += MPW_BITS;                                                     \
 144     _v++;                                                               \
 145     _max /= (mpd)MPW_MAX + 1;                                           \
 146   }                                                                     \
 147   if (!(_m->f & MP_NEG))                                                \
 148     _i = -_i;                                                           \
 149   (i) = _i;                                                             \
 150 } while (0)
 151
 152 /*----- Functions provided ------------------------------------------------*/
 153
 154 /* --- @mp_fromINT@ --- *
 155  *
 156  * Arguments:   @mp *d@ = pointer to destination multiprecision integer
 157  *              @INT i@ = standard C integer to convert
 158  *
 159  * Returns:     The resulting multiprecision integer.
 160  *
 161  * Use:         Converts a standard C integer to a multiprecision integer.
 162  */
 163
 164 #define mp_fromINT(name, type)                                          \
 165   extern mp *mp_from##name(mp */*d*/, type /*i*/)
 166
 167 mp_fromINT(short, short);
 168 mp_fromINT(ushort, unsigned short);
 169 mp_fromINT(int, int);
 170 mp_fromINT(uint, unsigned);
 171 mp_fromINT(long, long);
 172 mp_fromINT(ulong, unsigned long);
 173
 174 #undef mp_fromINT
 175
 176 /* --- @mp_toINT@ --- *
 177  *
 178  * Arguments:   @const mp *m@ = pointer to a multiprecision integer
 179  *
 180  * Returns:     The value of the integer @m@ as a C integer.
 181  *
 182  * Use:         Converts a multiprecision integer to a standard C integer.
 183  *              If the value of the multiprecision integer cannot be
 184  *              represented in the return type, and the return type is
 185  *              unsigned, it is reduced modulo @TYPE_MAX + 1@; if the return
 186  *              type is signed, the behaviour is undefined.
 187  */
 188
 189 #define mp_toINT(name, type)                                            \
 190   extern type mp_to##name(const mp */*m*/);
 191
 192 mp_toINT(short, short);
 193 mp_toINT(ushort, unsigned short);
 194 mp_toINT(int, int);
 195 mp_toINT(uint, unsigned);
 196 mp_toINT(long, long);
 197 mp_toINT(ulong, unsigned long);
 198
 199 #undef mp_toINT
 200
 201 /*----- That's all, folks -------------------------------------------------*/
 202
 203 #ifdef __cplusplus
 204   }
 205 #endif
 206
 207 #endif