Projective coordinates for prime curves

[u/mdw/catacomb] / f-prime.c

diff --git a/f-prime.c b/f-prime.c
index 0d76da0..7c1dae5 100644 (file)
--- a/f-prime.c
+++ b/f-prime.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: f-prime.c,v 1.3.4.1 2003/06/10 13:43:53 mdw Exp $
+ * $Id: f-prime.c,v 1.3.4.2 2004/03/20 00:13:31 mdw Exp $
  *
  * Prime fields with Montgomery arithmetic
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: f-prime.c,v $
+ * 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.
  *
@@ -82,6 +85,11 @@ static mp *fout(field *ff, mp *d, mp *x)
   return (mpmont_reduce(&f->mm, d, x));
 }
 
+static int fzerop(field *ff, mp *x)
+{
+  return (!MP_LEN(x));
+}
+
 static mp *fneg(field *ff, mp *d, mp *x)
 {
   fctx *f = (fctx *)ff;
@@ -157,11 +165,37 @@ static mp *ftpl(field *ff, mp *d, mp *x)
   return (d);
 }
 
+static mp *fqdl(field *ff, mp *d, mp *x)
+{
+  fctx *f = (fctx *)ff;
+  d = mp_lsl(d, x, 2);
+  while (MP_CMP(d, >, f->mm.m))
+    d = mp_sub(d, d, f->mm.m);
+  return (d);
+}
+
+static mp *fhlv(field *ff, mp *d, mp *x)
+{
+  fctx *f = (fctx *)ff;
+  if (!MP_LEN(x)) {
+    MP_COPY(x);
+    MP_DROP(d);
+    return (x);
+  }
+  if (x->v[0] & 1) {
+    d = mp_add(d, x, f->mm.m);
+    x = d;
+  }
+  return (mp_lsr(d, x, 1));
+}
+
 static mp *fsqrt(field *ff, mp *d, mp *x)
 {
   fctx *f = (fctx *)ff;
   d = mpmont_reduce(&f->mm, d, x);
   d = mp_modsqrt(d, d, f->mm.m);
+  if (!d)
+    return (d);
   return (mpmont_mul(&f->mm, d, d, f->mm.r2));
 }
 
@@ -170,8 +204,8 @@ static mp *fsqrt(field *ff, mp *d, mp *x)
 static field_ops fops = {
   fdestroy,
   fin, fout,
-  fneg, fadd, fsub, fmul, fsqr, finv, freduce,
-  fdbl, ftpl, fsqrt
+  fzerop, fneg, fadd, fsub, fmul, fsqr, finv, freduce,
+  fdbl, ftpl, fqdl, fhlv, fsqrt
 };
 
 /* --- @field_prime@ --- *