crypto: ge_cached_to_p2 implemented

src/crypto/crypto-ops.c

@@ -325,7 +325,7 @@ return 0 if f is in {0,2,4,...,q-1}
    |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
 */
 
-static int fe_isnegative(const fe f) {
+int fe_isnegative(const fe f) {
   unsigned char s[32];
   fe_tobytes(s, f);
   return s[0] & 1;
@@ -342,16 +342,6 @@ int fe_isnonzero(const fe f) {
     s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1;
 }
 
-int fe_cmp(const fe a, const fe b)
-{
-  for (size_t i = 9; i != SIZE_MAX; --i)
-  {
-    if ((const uint32_t)a[i] < (const uint32_t)b[i]) return -1;
-    if ((const uint32_t)a[i] > (const uint32_t)b[i]) return 1;
-  }
-  return 0;
-}
-
 /* From fe_mul.c */
 
 /*
@@ -970,7 +960,7 @@ Can overlap h with f or g.
    |h| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
 */
 
-static void fe_sub(fe h, const fe f, const fe g) {
+void fe_sub(fe h, const fe f, const fe g) {
   int32_t f0 = f[0];
   int32_t f1 = f[1];
   int32_t f2 = f[2];
@@ -4310,3 +4300,17 @@ void ge_scalarmult_vartime_p3_v2(ge_p3 *r, const unsigned char *a, const ge_p3 *
       ge_p1p1_to_p3(r, &t);
   }
 }
+
+
+void ge_cached_to_p2(ge_p2 *r, const ge_cached *c)
+{
+  static const fe inv2 = { 10, 0, 0, 0, 0, 0, 0, 0, 0, -16777216 };
+
+  fe_sub(r->X, c->YplusX, c->YminusX);
+  fe_mul(r->X, r->X, inv2);
+
+  fe_add(r->Y, c->YplusX, c->YminusX);
+  fe_mul(r->Y, r->Y, inv2);
+
+  fe_copy(r->Z, c->Z);
+}

src/crypto/crypto-ops.h

@@ -111,6 +111,7 @@ void ge_fromfe_frombytes_vartime(ge_p2 *, const unsigned char *);
 void ge_p2_to_p3(ge_p3 *r, const ge_p2 *t);
 void ge_bytes_hash_to_ec(ge_p3 *, const void *, size_t);
 void ge_bytes_hash_to_ec_32(ge_p3 *, const unsigned char *);
+void ge_cached_to_p2(ge_p2 *r, const ge_cached *c);
 
 void ge_p3_0(ge_p3 *h);
 void ge_sub(ge_p1p1 *, const ge_p3 *, const ge_cached *);
@@ -138,8 +139,9 @@ void sc_invert(unsigned char*, const unsigned char*);
 
 void fe_sq(fe h, const fe f);
 int fe_isnonzero(const fe f);
-int fe_cmp(const fe a, const fe b);
+void fe_sub(fe h, const fe f, const fe g);
 void fe_mul(fe, const fe, const fe);
 void fe_frombytes(fe h, const unsigned char *s);
 void fe_invert(fe out, const fe z);
 void fe_tobytes(unsigned char *s, const fe h);
+int fe_isnegative(const fe f);