/* -*-c-*-
*
- * $Id: ec-prime.c,v 1.4 2004/03/21 22:52:06 mdw Exp $
+ * $Id: ec-prime.c,v 1.5 2004/03/22 02:19:10 mdw Exp $
*
* Elliptic curves over prime fields
*
/*----- Revision history --------------------------------------------------*
*
* $Log: ec-prime.c,v $
+ * Revision 1.5 2004/03/22 02:19:10 mdw
+ * Rationalise the sliding-window threshold. Drop guarantee that right
+ * arguments to EC @add@ are canonical, and fix up projective implementations
+ * to cope.
+ *
* Revision 1.4 2004/03/21 22:52:06 mdw
* Merge and close elliptic curve branch.
*
EC_COPY(d, a);
else {
field *f = c->f;
- mp *p, *q, *r, *w, *u, *s, *dx, *dy, *dz;
+ mp *p, *q, *r, *w, *u, *uu, *s, *ss, *dx, *dy, *dz;
q = F_SQR(f, MP_NEW, a->z); /* %$z_0^2$% */
u = F_MUL(f, MP_NEW, q, b->x); /* %$u = x_1 z_0^2$% */
p = F_MUL(f, MP_NEW, q, b->y); /* %$y_1 z_0^2$% */
s = F_MUL(f, q, p, a->z); /* %$s = y_1 z_0^3$% */
- w = F_SUB(f, p, a->x, u); /* %$w = x_0 - u$% */
- r = F_SUB(f, MP_NEW, a->y, s); /* %$r = y_0 - s$% */
+ q = F_SQR(f, MP_NEW, b->z); /* %$z_1^2$% */
+ uu = F_MUL(f, MP_NEW, q, a->x); /* %$uu = x_0 z_1^2$%*/
+ p = F_MUL(f, p, q, a->y); /* %$y_0 z_1^2$% */
+ ss = F_MUL(f, q, p, b->z); /* %$ss = y_0 z_1^3$% */
+
+ w = F_SUB(f, p, uu, u); /* %$w = uu - u$% */
+ r = F_SUB(f, MP_NEW, ss, s); /* %$r = ss - s$% */
if (F_ZEROP(f, w)) {
MP_DROP(w);
MP_DROP(u);
MP_DROP(s);
+ MP_DROP(uu);
+ MP_DROP(ss);
if (F_ZEROP(f, r)) {
MP_DROP(r);
return (c->ops->dbl(c, d, a));
return (d);
}
}
- u = F_ADD(f, u, u, a->x); /* %$t = x_0 + u$% */
- s = F_ADD(f, s, s, a->y); /* %$m = y_0 + r$% */
+ u = F_ADD(f, u, u, uu); /* %$t = uu + u$% */
+ s = F_ADD(f, s, s, ss); /* %$m = ss + r$% */
- dz = F_MUL(f, MP_NEW, a->z, w); /* %$z' = z_0 w$% */
+ uu = F_MUL(f, uu, a->z, w); /* %$z_0 w$% */
+ dz = F_MUL(f, ss, uu, b->z); /* %$z' = z_0 z_1 w$% */
- p = F_SQR(f, MP_NEW, w); /* %$w^2$% */
+ p = F_SQR(f, uu, w); /* %$w^2$% */
q = F_MUL(f, MP_NEW, p, u); /* %$t w^2$% */
u = F_MUL(f, u, p, w); /* %$w^3$% */
p = F_MUL(f, p, u, s); /* %$m w^3$% */