Abstract out verify logic for fe_to_storage

Author: sipa

src/field.h

@@ -93,6 +93,7 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
 #  define secp256k1_fe_mul secp256k1_fe_impl_mul
 #  define secp256k1_fe_sqr secp256k1_fe_impl_sqr
 #  define secp256k1_fe_cmov secp256k1_fe_impl_cmov
+#  define secp256k1_fe_to_storage secp256k1_fe_impl_to_storage
 #endif /* !defined(VERIFY) */
 
 /** Normalize a field element.
@@ -263,7 +264,11 @@ static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a);
 /** Potentially faster version of secp256k1_fe_inv, without constant-time guarantee. */
 static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a);
 
-/** Convert a field element to the storage type. */
+/** Convert a field element to secp256k1_fe_storage.
+ *
+ * On input, a must be a valid normalized field element.
+ * Performs {r = a}.
+ */
 static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a);
 
 /** Convert a field element back from the storage type. */

src/field_10x26_impl.h

@@ -1145,10 +1145,7 @@ static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r,
     r->n[7] = (r->n[7] & mask0) | (a->n[7] & mask1);
 }
 
-static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->normalized);
-#endif
+static void secp256k1_fe_impl_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
     r->n[0] = a->n[0] | a->n[1] << 26;
     r->n[1] = a->n[1] >> 6 | a->n[2] << 20;
     r->n[2] = a->n[2] >> 12 | a->n[3] << 14;

src/field_5x52_impl.h

@@ -459,10 +459,7 @@ static SECP256K1_INLINE void secp256k1_fe_storage_cmov(secp256k1_fe_storage *r,
     r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
 }
 
-static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->normalized);
-#endif
+static void secp256k1_fe_impl_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
     r->n[0] = a->n[0] | a->n[1] << 52;
     r->n[1] = a->n[1] >> 12 | a->n[2] << 40;
     r->n[2] = a->n[2] >> 24 | a->n[3] << 28;

src/field_impl.h

@@ -336,6 +336,13 @@ SECP256K1_INLINE static void secp256k1_fe_cmov(secp256k1_fe *r, const secp256k1_
     }
     secp256k1_fe_verify(r);
 }
+
+static void secp256k1_fe_impl_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a);
+SECP256K1_INLINE static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a) {
+    secp256k1_fe_verify(a);
+    VERIFY_CHECK(a->normalized);
+    secp256k1_fe_impl_to_storage(r, a);
+}
 #endif /* defined(VERIFY) */
 
 #endif /* SECP256K1_FIELD_IMPL_H */