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

   1 /* -*-c-*-
   2  *
   3  * $Id: mpint.h,v 1.6 2004/04/08 01:36:15 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 #ifndef CATACOMB_MPINT_H
  31 #define CATACOMB_MPINT_H
  32
  33 #ifdef __cplusplus
  34   extern "C" {
  35 #endif
  36
  37 /*----- Header files ------------------------------------------------------*/
  38
  39 #include <limits.h>
  40
  41 #ifndef CATACOMB_MP_H
  42 #  include "mp.h"
  43 #endif
  44
  45 /*----- Generic translation macros ----------------------------------------*/
  46
  47 /* --- @MP_FROMINT@ --- *
  48  *
  49  * Arguments:   @d@ = destination multiprecision integer
  50  *              @type@ = type of integer which @i@ is
  51  *              @i@ = a standard C integer
  52  *
  53  * Use:         Stores the value of @i@ in @d@.  This macro is actually
  54  *              rather subtle in places.  Be careful what you change.
  55  */
  56
  57 #define MP_FROMINT(d, type, i) do {                                     \
  58   type _i = (i);                                                        \
  59   size_t _o = 0;                                                        \
  60   mp *_d = (d);                                                         \
  61   size_t _sz = 4;                                                       \
  62                                                                         \
  63   MP_DEST(_d, _sz, 0);                                                  \
  64   _d->f &= ~(MP_NEG | MP_UNDEF);                                        \
  65                                                                         \
  66   /* --- Set the sign on the MP --- *                                   \
  67    *                                                                    \
  68    * If the input integer is *not* negative, then negate it.  This      \
  69    * fixes a problem with two's complement machines where the most      \
  70    * negative value actually has larger magnitude than the most         \
  71    * positive, and hence -TYPE_MIN == TYPE_MIN but TYPE_MIN != 0.  If   \
  72    * all the work is carried out on negative numbers there isn't a      \
  73    * problem.                                                           \
  74    */                                                                   \
  75                                                                         \
  76   if (_i >= 0)                                                          \
  77     _i = -_i;                                                           \
  78   else                                                                  \
  79     _d->f |= MP_NEG;                                                    \
  80                                                                         \
  81   while (_i) {                                                          \
  82     if (_o == _sz) {                                                    \
  83       _sz <<= 1;                                                        \
  84       MP_ENSURE(_d, _sz);                                               \
  85     }                                                                   \
  86     _d->v[_o++] = MPW(-_i);                                             \
  87                                                                         \
  88     /* --- More subtlety --- *                                          \
  89      *                                                                  \
  90      * Ideally, I'd like to just shift @i@ right by @MPW_BITS@.  But I  \
  91      * can't, because that might be more than I'm allowed.  I can't     \
  92      * divide by @MPW_MAX + 1@ because that might turn out to be zero   \
  93      * in my current type, and besides which it's unsigned which messes \
  94      * up all of my negative arithmetic.  So do an explicit test here.  \
  95      */                                                                 \
  96                                                                         \
  97     if (_i >= -MPW_MAX)                                                 \
  98       break;                                                            \
  99     else                                                                \
 100       _i /= (type)MPW_MAX + 1;                                          \
 101   }                                                                     \
 102   _d->vl = _d->v + _o;                                                  \
 103   (d) = _d;                                                             \
 104 } while (0)
 105
 106 /* --- @MP_TOINT@ --- *
 107  *
 108  * Arguments:   @m@ = a multiprecision integer
 109  *              @type@ = the type of @i@
 110  *              @max@ = the largest value @i@ can represent
 111  *              @i@ = an integer variable
 112  *
 113  * Use:         Stores the value of a multiprecision integer in a standard C
 114  *              integer.  If the value won't fit, the behaviour is determined
 115  *              by the type of @i@: if @i@ is unsigned, the value of the
 116  *              multiprecision integer modulo @max + 1@ is stored; if @i@ is
 117  *              signed, the behaviour is undefined.
 118  *
 119  *              If you don't want to be bitten by these sorts of things, keep
 120  *              copies of @INT_MAX@ or whatever is appropriate in
 121  *              multiprecision form and compare before conversion.
 122  */
 123
 124 #define MP_TOINT(m, type, max, i) do {                                  \
 125   type _i = 0;                                                          \
 126   type _max = (max);                                                    \
 127   unsigned _s = 0;                                                      \
 128   const mp *_m = (m);                                                   \
 129   const mpw *_v = _m->v, *_vl = _m->vl;                                 \
 130                                                                         \
 131   /* --- Do all the arithmetic in negative numbers --- */               \
 132                                                                         \
 133   while (_v < _vl && _max > 0) {                                        \
 134     _i -= *_v << _s;                                                    \
 135     _s += MPW_BITS;                                                     \
 136     _v++;                                                               \
 137     _max /= (mpd)MPW_MAX + 1;                                           \
 138   }                                                                     \
 139   if (!(_m->f & MP_NEG))                                                \
 140     _i = -_i;                                                           \
 141   (i) = _i;                                                             \
 142 } while (0)
 143
 144 /*----- Functions provided ------------------------------------------------*/
 145
 146 /* --- @mp_fromINT@ --- *
 147  *
 148  * Arguments:   @mp *d@ = pointer to destination multiprecision integer
 149  *              @INT i@ = standard C integer to convert
 150  *
 151  * Returns:     The resulting multiprecision integer.
 152  *
 153  * Use:         Converts a standard C integer to a multiprecision integer.
 154  */
 155
 156 #define mp_fromINT(name, type)                                          \
 157   extern mp *mp_from##name(mp */*d*/, type /*i*/)
 158
 159 mp_fromINT(short, short);
 160 mp_fromINT(ushort, unsigned short);
 161 mp_fromINT(int, int);
 162 mp_fromINT(uint, unsigned);
 163 mp_fromINT(uint32, uint32);
 164 mp_fromINT(long, long);
 165 mp_fromINT(ulong, unsigned long);
 166
 167 #undef mp_fromINT
 168
 169 /* --- @mp_toINT@ --- *
 170  *
 171  * Arguments:   @const mp *m@ = pointer to a multiprecision integer
 172  *
 173  * Returns:     The value of the integer @m@ as a C integer.
 174  *
 175  * Use:         Converts a multiprecision integer to a standard C integer.
 176  *              If the value of the multiprecision integer cannot be
 177  *              represented in the return type, and the return type is
 178  *              unsigned, it is reduced modulo @TYPE_MAX + 1@; if the return
 179  *              type is signed, the behaviour is undefined.
 180  */
 181
 182 #define mp_toINT(name, type)                                            \
 183   extern type mp_to##name(const mp */*m*/)
 184
 185 mp_toINT(short, short);
 186 mp_toINT(ushort, unsigned short);
 187 mp_toINT(int, int);
 188 mp_toINT(uint, unsigned);
 189 mp_toINT(uint32, uint32);
 190 mp_toINT(long, long);
 191 mp_toINT(ulong, unsigned long);
 192
 193 #undef mp_toINT
 194
 195 /*----- That's all, folks -------------------------------------------------*/
 196
 197 #ifdef __cplusplus
 198   }
 199 #endif
 200
 201 #endif