ecc.[ch]: add elliptic-curve point_copy_into functions.

This will let my upcoming new test of memory access patterns run a
sequence of tests on different elliptic-curve data which is stored at
the same address each time.

ecc.c

@@ -112,6 +112,14 @@ WeierstrassPoint *ecc_weierstrass_point_new_identity(WeierstrassCurve *wc)
     return wp;
 }
 
+void ecc_weierstrass_point_copy_into(
+    WeierstrassPoint *dest, WeierstrassPoint *src)
+{
+    mp_copy_into(dest->X, src->X);
+    mp_copy_into(dest->Y, src->Y);
+    mp_copy_into(dest->Z, src->Z);
+}
+
 WeierstrassPoint *ecc_weierstrass_point_copy(WeierstrassPoint *orig)
 {
     WeierstrassPoint *wp = ecc_weierstrass_point_new_empty(orig->wc);
@@ -610,6 +618,13 @@ MontgomeryPoint *ecc_montgomery_point_new(MontgomeryCurve *mc, mp_int *x)
     return mp;
 }
 
+void ecc_montgomery_point_copy_into(
+    MontgomeryPoint *dest, MontgomeryPoint *src)
+{
+    mp_copy_into(dest->X, src->X);
+    mp_copy_into(dest->Z, src->Z);
+}
+
 MontgomeryPoint *ecc_montgomery_point_copy(MontgomeryPoint *orig)
 {
     MontgomeryPoint *mp = ecc_montgomery_point_new_empty(orig->mc);
@@ -904,6 +919,14 @@ EdwardsPoint *ecc_edwards_point_new(
         ec, monty_import(ec->mc, x), monty_import(ec->mc, y));
 }
 
+void ecc_edwards_point_copy_into(EdwardsPoint *dest, EdwardsPoint *src)
+{
+    mp_copy_into(dest->X, src->X);
+    mp_copy_into(dest->Y, src->Y);
+    mp_copy_into(dest->Z, src->Z);
+    mp_copy_into(dest->T, src->T);
+}
+
 EdwardsPoint *ecc_edwards_point_copy(EdwardsPoint *orig)
 {
     EdwardsPoint *ep = ecc_edwards_point_new_empty(orig->ec);

ecc.h

@@ -61,6 +61,8 @@ WeierstrassPoint *ecc_weierstrass_point_new_from_x(
     WeierstrassCurve *curve, mp_int *x, unsigned desired_y_parity);
 
 /* Memory management: copy and free points. */
+void ecc_weierstrass_point_copy_into(
+    WeierstrassPoint *dest, WeierstrassPoint *src);
 WeierstrassPoint *ecc_weierstrass_point_copy(WeierstrassPoint *wc);
 void ecc_weierstrass_point_free(WeierstrassPoint *point);
 
@@ -143,6 +145,8 @@ void ecc_montgomery_curve_free(MontgomeryCurve *);
  * explicitly represent the identity for this application.
  */
 MontgomeryPoint *ecc_montgomery_point_new(MontgomeryCurve *mc, mp_int *x);
+void ecc_montgomery_point_copy_into(
+    MontgomeryPoint *dest, MontgomeryPoint *src);
 MontgomeryPoint *ecc_montgomery_point_copy(MontgomeryPoint *orig);
 void ecc_montgomery_point_free(MontgomeryPoint *mp);
 
@@ -213,6 +217,7 @@ EdwardsPoint *ecc_edwards_point_new_from_y(
     EdwardsCurve *curve, mp_int *y, unsigned desired_x_parity);
 
 /* Copy and free points. */
+void ecc_edwards_point_copy_into(EdwardsPoint *dest, EdwardsPoint *src);
 EdwardsPoint *ecc_edwards_point_copy(EdwardsPoint *ec);
 void ecc_edwards_point_free(EdwardsPoint *point);