From 4c25f6efbd5f8b4738c1c16daf73906d45c5f579 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Fri, 28 Jan 2022 18:40:33 -0500
Subject: [PATCH] Abstract out verify logic for fe_mul

---
 src/field.h            | 11 +++++++++--
 src/field_10x26_impl.h | 15 +--------------
 src/field_5x52_impl.h  | 15 +--------------
 src/field_impl.h       | 14 ++++++++++++++
 4 files changed, 25 insertions(+), 30 deletions(-)

diff --git a/src/field.h b/src/field.h
index 988bc6f390..c301841b29 100644
--- a/src/field.h
+++ b/src/field.h
@@ -90,6 +90,7 @@ static const secp256k1_fe secp256k1_const_beta = SECP256K1_FE_CONST(
 #  define secp256k1_fe_negate secp256k1_fe_impl_negate
 #  define secp256k1_fe_mul_int secp256k1_fe_impl_mul_int
 #  define secp256k1_fe_add secp256k1_fe_impl_add
+#  define secp256k1_fe_mul secp256k1_fe_impl_mul
 #endif /* !defined(VERIFY) */
 
 /** Normalize a field element.
@@ -225,8 +226,14 @@ static void secp256k1_fe_mul_int(secp256k1_fe *r, int a);
  */
 static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_fe *a);
 
-/** Sets a field element to be the product of two others. Requires the inputs' magnitudes to be at most 8.
- *  The output magnitude is 1 (but not guaranteed to be normalized). */
+/** Multiply two field elements.
+ *
+ * On input, a and b must be valid field elements; r does not need to be initialized.
+ * r and a may point to the same object, but neither can be equal to b. The magnitudes
+ * of a and b must not exceed 8.
+ * Performs {r = a * b}
+ * On output, r will have magnitude 1, but won't be normalized.
+ */
 static void secp256k1_fe_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b);
 
 /** Sets a field element to be the square of another. Requires the input's magnitude to be at most 8.
diff --git a/src/field_10x26_impl.h b/src/field_10x26_impl.h
index eefd4da697..f2cc4ad1e3 100644
--- a/src/field_10x26_impl.h
+++ b/src/field_10x26_impl.h
@@ -1027,21 +1027,8 @@ SECP256K1_INLINE static void secp256k1_fe_sqr_inner(uint32_t *r, const uint32_t
 }
 #endif
 
-static void secp256k1_fe_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->magnitude <= 8);
-    VERIFY_CHECK(b->magnitude <= 8);
-    secp256k1_fe_verify(a);
-    secp256k1_fe_verify(b);
-    VERIFY_CHECK(r != b);
-    VERIFY_CHECK(a != b);
-#endif
+SECP256K1_INLINE static void secp256k1_fe_impl_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b) {
     secp256k1_fe_mul_inner(r->n, a->n, b->n);
-#ifdef VERIFY
-    r->magnitude = 1;
-    r->normalized = 0;
-    secp256k1_fe_verify(r);
-#endif
 }
 
 static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_fe *a) {
diff --git a/src/field_5x52_impl.h b/src/field_5x52_impl.h
index 8bd084ff27..adfac57778 100644
--- a/src/field_5x52_impl.h
+++ b/src/field_5x52_impl.h
@@ -361,21 +361,8 @@ SECP256K1_INLINE static void secp256k1_fe_impl_add(secp256k1_fe *r, const secp25
     r->n[4] += a->n[4];
 }
 
-static void secp256k1_fe_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b) {
-#ifdef VERIFY
-    VERIFY_CHECK(a->magnitude <= 8);
-    VERIFY_CHECK(b->magnitude <= 8);
-    secp256k1_fe_verify(a);
-    secp256k1_fe_verify(b);
-    VERIFY_CHECK(r != b);
-    VERIFY_CHECK(a != b);
-#endif
+SECP256K1_INLINE static void secp256k1_fe_impl_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b) {
     secp256k1_fe_mul_inner(r->n, a->n, b->n);
-#ifdef VERIFY
-    r->magnitude = 1;
-    r->normalized = 0;
-    secp256k1_fe_verify(r);
-#endif
 }
 
 static void secp256k1_fe_sqr(secp256k1_fe *r, const secp256k1_fe *a) {
diff --git a/src/field_impl.h b/src/field_impl.h
index 172b846d89..0def1e57d5 100644
--- a/src/field_impl.h
+++ b/src/field_impl.h
@@ -286,6 +286,20 @@ SECP256K1_INLINE static void secp256k1_fe_add(secp256k1_fe *r, const secp256k1_f
     r->normalized = 0;
     secp256k1_fe_verify(r);
 }
+
+static void secp256k1_fe_impl_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b);
+SECP256K1_INLINE static void secp256k1_fe_mul(secp256k1_fe *r, const secp256k1_fe *a, const secp256k1_fe * SECP256K1_RESTRICT b) {
+    secp256k1_fe_verify(a);
+    secp256k1_fe_verify(b);
+    VERIFY_CHECK(a->magnitude <= 8);
+    VERIFY_CHECK(b->magnitude <= 8);
+    VERIFY_CHECK(r != b);
+    VERIFY_CHECK(a != b);
+    secp256k1_fe_impl_mul(r, a, b);
+    r->magnitude = 1;
+    r->normalized = 0;
+    secp256k1_fe_verify(r);
+}
 #endif /* defined(VERIFY) */
 
 #endif /* SECP256K1_FIELD_IMPL_H */