X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/4edc47b89bc56cd4041fdb0f4e8e892acd589ed8..02d7884df1f33c9c7dc3a14c4b1a5f520ebe090a:/f-prime.c

diff --git a/f-prime.c b/f-prime.c
index 088032b..43d6da3 100644
--- a/f-prime.c
+++ b/f-prime.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: f-prime.c,v 1.9 2004/04/01 21:28:41 mdw Exp $
+ * $Id: f-prime.c,v 1.11 2004/04/03 03:32:05 mdw Exp $
  *
  * Prime fields with Montgomery arithmetic
  *
@@ -30,6 +30,12 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: f-prime.c,v $
+ * Revision 1.11  2004/04/03 03:32:05  mdw
+ * General robustification.
+ *
+ * Revision 1.10  2004/04/02 01:03:49  mdw
+ * Miscellaneous constification.
+ *
  * 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
@@ -175,7 +181,7 @@ static mp *fhlv(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,
@@ -188,7 +194,7 @@ static field_ops fops = {
  *
  * 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.
@@ -196,7 +202,11 @@ static field_ops fops = {
 
 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;