merge in notes on elligator; move some point ops to ec_point

src/ec_point.c

@@ -827,6 +827,18 @@ elligator_2s_inject (
     IF32( field_weak_reduce(   &L7 ) );
     field_mulw_scc (   &L6, &a->y, -2-2*EDWARDS_D );
     field_mul  (   &L5,   &L7,   &L6 );
+        /* FIXME Stability problem (API stability, not crash) / possible bug.
+         * change to: p448_mul  (   &L5,   &L7,   &L4 ); ?
+         * This isn't a deep change: it's for sign adjustment.
+         * Need to check which one leads to the correct sign, probably by writig
+         * the invert routine.
+         *
+         * Also, the tool doesn't produce the optimal route to this.
+         * Let incoming L6 = a, L7 = e, L4 = b.
+         *
+         * Could compute be, (be)^2, (be)^3, a b^3 e^3, a b^3 e^4. = 4M+S
+         * instead of 6M.
+         */
     field_mul  (   &L8,   &L5,   &L4 );
     field_mul  (   &L4,   &L5,   &L6 );
     field_mul  (   &L5,   &L7,   &L8 );

src/include/ec_point.h

@@ -481,6 +481,30 @@ validate_extensible (
     const struct extensible_t* ext
 );
 
+/**
+ * If doNegate, then negate a twisted niels point.
+ */
+static __inline__ void
+__attribute__((unused))
+cond_negate_tw_niels (
+    struct tw_niels_t *n,
+    mask_t doNegate
+) {
+    field_cond_swap(&n->a, &n->b, doNegate);
+    field_cond_neg(&n->c, doNegate);
+}
+
+/**
+ * If doNegate, then negate a twisted projective niels point.
+ */
+static __inline__ void
+__attribute__((unused))
+cond_negate_tw_pniels (
+    struct tw_pniels_t *n,
+    mask_t doNegate
+) {
+    cond_negate_tw_niels(&n->n, doNegate);
+}
 
 void
 copy_affine (

src/scalarmul.c

@@ -47,23 +47,6 @@ montgomery_ladder (
     return serialize_montgomery(out, &mont, in);
 }
 
-static __inline__ void
-cond_negate_tw_niels (
-    struct tw_niels_t *n,
-    mask_t doNegate
-) {
-    field_cond_swap(&n->a, &n->b, doNegate);
-    field_cond_neg(&n->c, doNegate);
-}
-
-static __inline__ void
-cond_negate_tw_pniels (
-    struct tw_pniels_t *n,
-    mask_t doNegate
-) {
-    cond_negate_tw_niels(&n->n, doNegate);
-}
-
 static __inline__ void
 constant_time_lookup_tw_pniels (
     struct tw_pniels_t *out,