/* -*-c-*-
*
- * $Id: f-prime.c,v 1.9 2004/04/01 21:28:41 mdw Exp $
+ * $Id: f-prime.c,v 1.12 2004/04/08 01:36:15 mdw Exp $
*
* Prime fields with Montgomery arithmetic
*
* MA 02111-1307, USA.
*/
-/*----- Revision history --------------------------------------------------*
- *
- * $Log: f-prime.c,v $
- * Revision 1.9 2004/04/01 21:28:41 mdw
- * Normal basis support (translates to poly basis internally). Rewrite
- * EC and prime group table generators in awk, so that they can reuse data
- * for repeated constants.
- *
- * Revision 1.8 2004/04/01 12:50:09 mdw
- * Add cyclic group abstraction, with test code. Separate off exponentation
- * functions for better static linking. Fix a buttload of bugs on the way.
- * Generally ensure that negative exponents do inversion correctly. Add
- * table of standard prime-field subgroups. (Binary field subgroups are
- * currently unimplemented but easy to add if anyone ever finds a good one.)
- *
- * Revision 1.7 2004/03/27 17:54:11 mdw
- * Standard curves and curve checking.
- *
- * Revision 1.6 2004/03/23 15:19:32 mdw
- * Test elliptic curves more thoroughly.
- *
- * Revision 1.5 2004/03/23 12:08:26 mdw
- * Random field-element selection.
- *
- * Revision 1.4 2004/03/21 22:52:06 mdw
- * Merge and close elliptic curve branch.
- *
- * Revision 1.3.4.3 2004/03/21 22:39:46 mdw
- * Elliptic curves on binary fields work.
- *
- * Revision 1.3.4.2 2004/03/20 00:13:31 mdw
- * Projective coordinates for prime curves
- *
- * Revision 1.3.4.1 2003/06/10 13:43:53 mdw
- * Simple (non-projective) curves over prime fields now seem to work.
- *
- * Revision 1.3 2003/05/15 23:25:59 mdw
- * Make elliptic curve stuff build.
- *
- * Revision 1.2 2002/01/13 13:48:44 mdw
- * Further progress.
- *
- * Revision 1.1 2001/04/29 18:12:33 mdw
- * Prototype version.
- *
- */
-
/*----- Header files ------------------------------------------------------*/
#include <mLib/sub.h>
static mp *finv(field *ff, mp *d, mp *x) {
fctx *f = (fctx *)ff; d = mpmont_reduce(&f->mm, d, x);
- mp_gcd(0, 0, &d, f->mm.m, d); return (mpmont_mul(&f->mm, d, d, f->mm.r2));
+ d = mp_modinv(d, d, f->mm.m); return (mpmont_mul(&f->mm, d, d, f->mm.r2));
}
static mp *freduce(field *ff, mp *d, mp *x)
/* --- Field operations table --- */
-static field_ops fops = {
+static const field_ops fops = {
FTY_PRIME, "prime",
fdestroy, frand, field_stdsamep,
fin, fout,
*
* Arguments: @mp *p@ = the characteristic of the field
*
- * Returns: A pointer to the field.
+ * Returns: A pointer to the field or null.
*
* Use: Creates a field structure for a prime field of size %$p$%,
* using Montgomery reduction for arithmetic.
field *field_prime(mp *p)
{
- fctx *f = CREATE(fctx);
+ fctx *f;
+
+ if (!MP_ISPOS(p) || !MP_ISODD(p))
+ return (0);
+ f = CREATE(fctx);
f->f.ops = &fops;
mpmont_create(&f->mm, p);
f->f.zero = MP_ZERO;