Abstract out verify logic for fe_from_storage

Author: sipa

src/field.h

@@ -97,6 +97,7 @@ static void secp256k1_fe_verify(const secp256k1_fe *a);
 #  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
+#  define secp256k1_fe_from_storage secp256k1_fe_impl_from_storage
 #endif /* defined(VERIFY) */
 
 /** Normalize a field element.
@@ -271,7 +272,12 @@ static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a);
  */
 static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, const secp256k1_fe *a);
 
-/** Convert a field element back from the storage type. */
+/** Convert a field element back from secp256k1_fe_storage.
+ *
+ * On input, r need not be initialized.
+ * Performs {r = a}.
+ * On output, r will be normalized and will have magnitude 1.
+ */
 static void secp256k1_fe_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a);
 
 /** If flag is true, set *r equal to *a; otherwise leave it. Constant-time.  Both *r and *a must be initialized.*/

src/field_10x26_impl.h

@@ -1140,7 +1140,7 @@ static void secp256k1_fe_impl_to_storage(secp256k1_fe_storage *r, const secp256k
     r->n[7] = a->n[8] >> 16 | a->n[9] << 10;
 }
 
-static SECP256K1_INLINE void secp256k1_fe_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a) {
+static SECP256K1_INLINE void secp256k1_fe_impl_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a) {
     r->n[0] = a->n[0] & 0x3FFFFFFUL;
     r->n[1] = a->n[0] >> 26 | ((a->n[1] << 6) & 0x3FFFFFFUL);
     r->n[2] = a->n[1] >> 20 | ((a->n[2] << 12) & 0x3FFFFFFUL);
@@ -1151,11 +1151,6 @@ static SECP256K1_INLINE void secp256k1_fe_from_storage(secp256k1_fe *r, const se
     r->n[7] = a->n[5] >> 22 | ((a->n[6] << 10) & 0x3FFFFFFUL);
     r->n[8] = a->n[6] >> 16 | ((a->n[7] << 16) & 0x3FFFFFFUL);
     r->n[9] = a->n[7] >> 10;
-#ifdef VERIFY
-    r->magnitude = 1;
-    r->normalized = 1;
-    secp256k1_fe_verify(r);
-#endif
 }
 
 static void secp256k1_fe_from_signed30(secp256k1_fe *r, const secp256k1_modinv32_signed30 *a) {

src/field_5x52_impl.h

@@ -454,17 +454,12 @@ static void secp256k1_fe_impl_to_storage(secp256k1_fe_storage *r, const secp256k
     r->n[3] = a->n[3] >> 36 | a->n[4] << 16;
 }
 
-static SECP256K1_INLINE void secp256k1_fe_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a) {
+static SECP256K1_INLINE void secp256k1_fe_impl_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a) {
     r->n[0] = a->n[0] & 0xFFFFFFFFFFFFFULL;
     r->n[1] = a->n[0] >> 52 | ((a->n[1] << 12) & 0xFFFFFFFFFFFFFULL);
     r->n[2] = a->n[1] >> 40 | ((a->n[2] << 24) & 0xFFFFFFFFFFFFFULL);
     r->n[3] = a->n[2] >> 28 | ((a->n[3] << 36) & 0xFFFFFFFFFFFFFULL);
     r->n[4] = a->n[3] >> 16;
-#ifdef VERIFY
-    r->magnitude = 1;
-    r->normalized = 1;
-    secp256k1_fe_verify(r);
-#endif
 }
 
 static void secp256k1_fe_from_signed62(secp256k1_fe *r, const secp256k1_modinv64_signed62 *a) {

src/field_impl.h

@@ -335,6 +335,14 @@ SECP256K1_INLINE static void secp256k1_fe_to_storage(secp256k1_fe_storage *r, co
     VERIFY_CHECK(a->normalized);
     secp256k1_fe_impl_to_storage(r, a);
 }
+
+static void secp256k1_fe_impl_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a);
+SECP256K1_INLINE static void secp256k1_fe_from_storage(secp256k1_fe *r, const secp256k1_fe_storage *a) {
+    secp256k1_fe_impl_from_storage(r, a);
+    r->magnitude = 1;
+    r->normalized = 1;
+    secp256k1_fe_verify(r);
+}
 #endif /* defined(VERIFY) */
 
 #endif /* SECP256K1_FIELD_IMPL_H */