Make the curve B constant a secp256k1_fe

Author: sipa

src/group_impl.h

@@ -14,7 +14,7 @@
 /* These points can be generated in sage as follows:
  *
  * 0. Setup a worksheet with the following parameters.
- *   b = 4  # whatever CURVE_B will be set to
+ *   b = 4  # whatever secp256k1_fe_const_b will be set to
  *   F = FiniteField (0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F)
  *   C = EllipticCurve ([F (0), F (b)])
  *
@@ -45,15 +45,18 @@ static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_GE_CONST(
     0x48DF246C, 0x808DAE72, 0xCFE52572, 0x7F0501ED
 );
 
-static const int CURVE_B = 4;
+static const secp256k1_fe secp256k1_fe_const_b = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 4);
+
 #  elif EXHAUSTIVE_TEST_ORDER == 13
 static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_GE_CONST(
     0xedc60018, 0xa51a786b, 0x2ea91f4d, 0x4c9416c0,
     0x9de54c3b, 0xa1316554, 0x6cf4345c, 0x7277ef15,
     0x54cb1b6b, 0xdc8c1273, 0x087844ea, 0x43f4603e,
     0x0eaf9a43, 0xf6effe55, 0x939f806d, 0x37adf8ac
 );
-static const int CURVE_B = 2;
+
+static const secp256k1_fe secp256k1_fe_const_b = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 2);
+
 #  else
 #    error No known generator for the specified exhaustive test group order.
 #  endif
@@ -68,7 +71,7 @@ static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_GE_CONST(
     0xFD17B448UL, 0xA6855419UL, 0x9C47D08FUL, 0xFB10D4B8UL
 );
 
-static const int CURVE_B = 7;
+static const secp256k1_fe secp256k1_fe_const_b = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 7);
 #endif
 
 static void secp256k1_ge_set_gej_zinv(secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_fe *zi) {
@@ -219,14 +222,13 @@ static void secp256k1_ge_clear(secp256k1_ge *r) {
 }
 
 static int secp256k1_ge_set_xquad(secp256k1_ge *r, const secp256k1_fe *x) {
-    secp256k1_fe x2, x3, c;
+    secp256k1_fe x2, x3;
     r->x = *x;
     secp256k1_fe_sqr(&x2, x);
     secp256k1_fe_mul(&x3, x, &x2);
     r->infinity = 0;
-    secp256k1_fe_set_int(&c, CURVE_B);
-    secp256k1_fe_add(&c, &x3);
-    return secp256k1_fe_sqrt(&r->y, &c);
+    secp256k1_fe_add(&x3, &secp256k1_fe_const_b);
+    return secp256k1_fe_sqrt(&r->y, &x3);
 }
 
 static int secp256k1_ge_set_xo_var(secp256k1_ge *r, const secp256k1_fe *x, int odd) {
@@ -270,15 +272,14 @@ static int secp256k1_gej_is_infinity(const secp256k1_gej *a) {
 }
 
 static int secp256k1_ge_is_valid_var(const secp256k1_ge *a) {
-    secp256k1_fe y2, x3, c;
+    secp256k1_fe y2, x3;
     if (a->infinity) {
         return 0;
     }
     /* y^2 = x^3 + 7 */
     secp256k1_fe_sqr(&y2, &a->y);
     secp256k1_fe_sqr(&x3, &a->x); secp256k1_fe_mul(&x3, &x3, &a->x);
-    secp256k1_fe_set_int(&c, CURVE_B);
-    secp256k1_fe_add(&x3, &c);
+    secp256k1_fe_add(&x3, &secp256k1_fe_const_b);
     secp256k1_fe_normalize_weak(&x3);
     return secp256k1_fe_equal_var(&y2, &x3);
 }