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

   1 /* -*-c-*-
   2  *
   3  * $Id: f-prime.c,v 1.2 2002/01/13 13:48:44 mdw Exp $
   4  *
   5  * Prime fields with Montgomery arithmetic
   6  *
   7  * (c) 2001 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: f-prime.c,v $
  33  * Revision 1.2  2002/01/13 13:48:44  mdw
  34  * Further progress.
  35  *
  36  * Revision 1.1  2001/04/29 18:12:33  mdw
  37  * Prototype version.
  38  *
  39  */
  40
  41 /*----- Header files ------------------------------------------------------*/
  42
  43 #include <mLib/sub.h>
  44
  45 #include "field.h"
  46 #include "mpmont.h"
  47
  48 /*----- Data structures ---------------------------------------------------*/
  49
  50 typedef struct fctx {
  51   field f;
  52   mpmont mm;
  53 } fctx;
  54
  55 /*----- Main code ---------------------------------------------------------*/
  56
  57 /* --- Field operations --- */
  58
  59 static void fdestroy(field *ff)
  60 {
  61   fctx *f = (fctx *)ff;
  62   mpmont_destroy(&f->mm);
  63   DESTROY(f);
  64 }
  65
  66 static mp *fin(field *ff, mp *d, mp *x)
  67 {
  68   fctx *f = (fctx *)ff;
  69   return (mpmont_mul(&f->mm, d, x, f->mm.r2));
  70 }
  71
  72 static mp *fout(field *ff, mp *d, mp *x)
  73 {
  74   fctx *f = (fctx *)ff;
  75   return (mpmont_reduce(&f->mm, d, x));
  76 }
  77
  78 static mp *fneg(field *ff, mp *d, mp *x)
  79 {
  80   fctx *f = (fctx *)ff;
  81   return (mp_sub(d, f->mm.m, x));
  82 }
  83
  84 static mp *fadd(field *ff, mp *d, mp *x, mp *y)
  85 {
  86   return (mp_add(d, x, y));
  87 }
  88
  89 static mp *fsub(field *ff, mp *d, mp *x, mp *y)
  90 {
  91   return (mp_sub(d, x, y));
  92 }
  93
  94 static mp *fmul(field *ff, mp *d, mp *x, mp *y)
  95 {
  96   fctx *f = (fctx *)ff;
  97   return (mpmont_mul(&f->mm, d, x, y));
  98 }
  99
 100 static mp *fsqr(field *ff, mp *d, mp *x)
 101 {
 102   fctx *f = (fctx *)ff;
 103   d = mp_sqr(d, x);
 104   return (mpmont_reduce(&f->mm, d, d));
 105 }
 106
 107 static mp *finv(field *ff, mp *d, mp *x)
 108 {
 109   fctx *f = (fctx *)ff;
 110   d = mpmont_reduce(&f->mm, x);
 111   mp_gcd(0, 0, &d, f->mm.m, d);
 112   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 113 }
 114
 115 static mp *freduce(field *ff, mp *d, mp *x)
 116 {
 117   fctx *f = (fctx *)ff;
 118   mp_div(0, &d, x, f->mm.m);
 119   return (d);
 120 }
 121
 122 static mp *fdbl(field *ff, mp *d, mp *x)
 123 {
 124   fctx *f = (fctx *)ff;
 125   return (mp_lsl(d, x, 1));
 126 }
 127
 128 static mp *ftpl(field *ff, mp *d, mp *x)
 129 {
 130   fctx *f = (fctx *)ff;
 131   MP_DEST(d, MP_LEN(x) + 1, x->f);
 132   MPX_UMULN(d->v, d->vl, x->v, x->vl, 3);
 133   return (d);
 134 }
 135
 136 static mp *fsqrt(field *ff, mp *d, mp *x)
 137 {
 138   fctx *f = (fctx *)ff;
 139   d = mpmont_reduce(&f->mm, x);
 140   d = mp_modsqrt(d, d, f->mm.m);
 141   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 142 }
 143
 144 /* --- Field operations table --- */
 145
 146 static field_ops fops = {
 147   fdestroy,
 148   fin, fout,
 149   fneg, fadd, fsub, fmul, fsqr, finv, freduce,
 150   fdbl, ftpl, fsqrt
 151 };
 152
 153 /* --- @field_prime@ --- *
 154  *
 155  * Arguments:   @mp *p@ = the characteristic of the field
 156  *
 157  * Returns:     A pointer to the field.
 158  *
 159  * Use:         Creates a field structure for a prime field of size %$p$%,
 160  *              using Montgomery reduction for arithmetic.
 161  */
 162
 163 field *field_prime(mp *p)
 164 {
 165   ftcx *f = CREATE(fctx);
 166   f->f.ops = &fops;
 167   mpmont_create(&f->mm, p);
 168   f->zero = MP_ZERO;
 169   f->one = &f->mm.r;
 170   return (&f->f);
 171 }
 172
 173 /*----- That's all, folks -------------------------------------------------*/