Abstract out verify logic for fe_normalizes_to_zero{,_var}

Author: sipa

src/field.h

@@ -78,6 +78,8 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
 #  define secp256k1_fe_normalize secp256k1_fe_impl_normalize
 #  define secp256k1_fe_normalize_weak secp256k1_fe_impl_normalize_weak
 #  define secp256k1_fe_normalize_var secp256k1_fe_impl_normalize_var
+#  define secp256k1_fe_normalizes_to_zero secp256k1_fe_impl_normalizes_to_zero
+#  define secp256k1_fe_normalizes_to_zero_var secp256k1_fe_impl_normalizes_to_zero_var
 #endif /* !defined(VERIFY) */
 
 /** Normalize a field element.
@@ -100,11 +102,17 @@ static void secp256k1_fe_normalize_weak(secp256k1_fe *r);
  */
 static void secp256k1_fe_normalize_var(secp256k1_fe *r);
 
-/** Verify whether a field element represents zero i.e. would normalize to a zero value. */
+/** Determine whether r represents field element 0.
+ *
+ * On input, r must be a valid field element.
+ * Returns whether r = 0 (mod p).
+ */
 static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r);
 
-/** Verify whether a field element represents zero i.e. would normalize to a zero value,
- *  without constant-time guarantee. */
+/** Determine whether r represents field element 0, without constant-time guarantee.
+ *
+ * Identical in behavior to secp256k1_normalizes_to_zero, but not constant time in r.
+ */
 static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r);
 
 /** Set a field element equal to a small (not greater than 0x7FFF), non-negative integer.

src/field_10x26_impl.h

@@ -183,7 +183,7 @@ static void secp256k1_fe_impl_normalize_var(secp256k1_fe *r) {
     r->n[5] = t5; r->n[6] = t6; r->n[7] = t7; r->n[8] = t8; r->n[9] = t9;
 }
 
-static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {
+static int secp256k1_fe_impl_normalizes_to_zero(const secp256k1_fe *r) {
     uint32_t t0 = r->n[0], t1 = r->n[1], t2 = r->n[2], t3 = r->n[3], t4 = r->n[4],
              t5 = r->n[5], t6 = r->n[6], t7 = r->n[7], t8 = r->n[8], t9 = r->n[9];
 
@@ -212,7 +212,7 @@ static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {
     return (z0 == 0) | (z1 == 0x3FFFFFFUL);
 }
 
-static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
+static int secp256k1_fe_impl_normalizes_to_zero_var(const secp256k1_fe *r) {
     uint32_t t0, t1, t2, t3, t4, t5, t6, t7, t8, t9;
     uint32_t z0, z1;
     uint32_t x;

src/field_5x52_impl.h

@@ -146,7 +146,7 @@ static void secp256k1_fe_impl_normalize_var(secp256k1_fe *r) {
     r->n[0] = t0; r->n[1] = t1; r->n[2] = t2; r->n[3] = t3; r->n[4] = t4;
 }
 
-static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {
+static int secp256k1_fe_impl_normalizes_to_zero(const secp256k1_fe *r) {
     uint64_t t0 = r->n[0], t1 = r->n[1], t2 = r->n[2], t3 = r->n[3], t4 = r->n[4];
 
     /* z0 tracks a possible raw value of 0, z1 tracks a possible raw value of P */
@@ -169,7 +169,7 @@ static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {
     return (z0 == 0) | (z1 == 0xFFFFFFFFFFFFFULL);
 }
 
-static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
+static int secp256k1_fe_impl_normalizes_to_zero_var(const secp256k1_fe *r) {
     uint64_t t0, t1, t2, t3, t4;
     uint64_t z0, z1;
     uint64_t x;

src/field_impl.h

@@ -173,6 +173,18 @@ SECP256K1_INLINE static void secp256k1_fe_normalize_var(secp256k1_fe *r) {
     r->normalized = 1;
     secp256k1_fe_verify(r);
 }
+
+static int secp256k1_fe_impl_normalizes_to_zero(const secp256k1_fe *r);
+SECP256K1_INLINE static int secp256k1_fe_normalizes_to_zero(const secp256k1_fe *r) {
+    secp256k1_fe_verify(r);
+    return secp256k1_fe_impl_normalizes_to_zero(r);
+}
+
+static int secp256k1_fe_impl_normalizes_to_zero_var(const secp256k1_fe *r);
+SECP256K1_INLINE static int secp256k1_fe_normalizes_to_zero_var(const secp256k1_fe *r) {
+    secp256k1_fe_verify(r);
+    return secp256k1_fe_impl_normalizes_to_zero_var(r);
+}
 #endif /* defined(VERIFY) */
 
 #endif /* SECP256K1_FIELD_IMPL_H */