add a version of ge_double_scalarmult_precomp_vartime with A precomp

src/crypto/crypto-ops.c

@@ -2000,17 +2000,15 @@ void ge_scalarmult(ge_p2 *r, const unsigned char *a, const ge_p3 *A) {
   }
 }
 
-void ge_double_scalarmult_precomp_vartime(ge_p2 *r, const unsigned char *a, const ge_p3 *A, const unsigned char *b, const ge_dsmp Bi) {
+void ge_double_scalarmult_precomp_vartime2(ge_p2 *r, const unsigned char *a, const ge_dsmp Ai, const unsigned char *b, const ge_dsmp Bi) {
   signed char aslide[256];
   signed char bslide[256];
-  ge_dsmp Ai; /* A, 3A, 5A, 7A, 9A, 11A, 13A, 15A */
   ge_p1p1 t;
   ge_p3 u;
   int i;
 
   slide(aslide, a);
   slide(bslide, b);
-  ge_dsm_precomp(Ai, A);
 
   ge_p2_0(r);
 
@@ -2041,6 +2039,13 @@ void ge_double_scalarmult_precomp_vartime(ge_p2 *r, const unsigned char *a, cons
   }
 }
 
+void ge_double_scalarmult_precomp_vartime(ge_p2 *r, const unsigned char *a, const ge_p3 *A, const unsigned char *b, const ge_dsmp Bi) {
+  ge_dsmp Ai; /* A, 3A, 5A, 7A, 9A, 11A, 13A, 15A */
+
+  ge_dsm_precomp(Ai, A);
+  ge_double_scalarmult_precomp_vartime2(r, a, Ai, b, Bi);
+}
+
 void ge_mul8(ge_p1p1 *r, const ge_p2 *t) {
   ge_p2 u;
   ge_p2_dbl(r, t);

src/crypto/crypto-ops.h

@@ -128,6 +128,7 @@ void sc_reduce(unsigned char *);
 
 void ge_scalarmult(ge_p2 *, const unsigned char *, const ge_p3 *);
 void ge_double_scalarmult_precomp_vartime(ge_p2 *, const unsigned char *, const ge_p3 *, const unsigned char *, const ge_dsmp);
+void ge_double_scalarmult_precomp_vartime2(ge_p2 *, const unsigned char *, const ge_dsmp, const unsigned char *, const ge_dsmp);
 void ge_mul8(ge_p1p1 *, const ge_p2 *);
 extern const fe fe_ma2;
 extern const fe fe_ma;

src/ringct/rctOps.cpp

@@ -262,6 +262,15 @@ namespace rct {
         ge_tobytes(aAbB.bytes, &rv);
     }
 
+    //addKeys3
+    //aAbB = a*A + b*B where a, b are scalars, A, B are curve points
+    //A and B must be input after applying "precomp"
+    void addKeys3(key &aAbB, const key &a, const ge_dsmp A, const key &b, const ge_dsmp B) {
+        ge_p2 rv;
+        ge_double_scalarmult_precomp_vartime2(&rv, a.bytes, A, b.bytes, B);
+        ge_tobytes(aAbB.bytes, &rv);
+    }
+
 
     //subtract Keys (subtracts curve points)
     //AB = A - B where A, B are curve points

src/ringct/rctOps.h

@@ -134,6 +134,7 @@ namespace rct {
     //aAbB = a*A + b*B where a, b are scalars, A, B are curve points
     //B must be input after applying "precomp"
     void addKeys3(key &aAbB, const key &a, const key &A, const key &b, const ge_dsmp B);
+    void addKeys3(key &aAbB, const key &a, const ge_dsmp A, const key &b, const ge_dsmp B);
     //AB = A - B where A, B are curve points
     void subKeys(key &AB, const key &A, const  key &B);
     //checks if A, B are equal as curve points