From 436281afdcb68991395f97338197d208212965e2 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Sun, 11 Oct 2020 15:41:54 -0700
Subject: [PATCH] Move secp256k1_fe_inverse{_var} to per-impl files

This temporarily duplicates the inversion code across the 5x52 and 10x26
implementations. Those implementations will be replaced in a next commit.
---
 src/field_10x26_impl.h | 127 +++++++++++++++++++++++++++++++++++++++++
 src/field_5x52_impl.h  | 127 +++++++++++++++++++++++++++++++++++++++++
 src/field_impl.h       | 127 -----------------------------------------
 3 files changed, 254 insertions(+), 127 deletions(-)

diff --git a/src/field_10x26_impl.h b/src/field_10x26_impl.h
index 62bffdc21b..3539d5b89f 100644
--- a/src/field_10x26_impl.h
+++ b/src/field_10x26_impl.h
@@ -1164,4 +1164,131 @@ static SECP256K1_INLINE void secp256k1_fe_from_storage(secp256k1_fe *r, const se
 #endif
 }
 
+static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a) {
+    secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
+    int j;
+
+    /** The binary representation of (p - 2) has 5 blocks of 1s, with lengths in
+     *  { 1, 2, 22, 223 }. Use an addition chain to calculate 2^n - 1 for each block:
+     *  [1], [2], 3, 6, 9, 11, [22], 44, 88, 176, 220, [223]
+     */
+
+    secp256k1_fe_sqr(&x2, a);
+    secp256k1_fe_mul(&x2, &x2, a);
+
+    secp256k1_fe_sqr(&x3, &x2);
+    secp256k1_fe_mul(&x3, &x3, a);
+
+    x6 = x3;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x6, &x6);
+    }
+    secp256k1_fe_mul(&x6, &x6, &x3);
+
+    x9 = x6;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x9, &x9);
+    }
+    secp256k1_fe_mul(&x9, &x9, &x3);
+
+    x11 = x9;
+    for (j=0; j<2; j++) {
+        secp256k1_fe_sqr(&x11, &x11);
+    }
+    secp256k1_fe_mul(&x11, &x11, &x2);
+
+    x22 = x11;
+    for (j=0; j<11; j++) {
+        secp256k1_fe_sqr(&x22, &x22);
+    }
+    secp256k1_fe_mul(&x22, &x22, &x11);
+
+    x44 = x22;
+    for (j=0; j<22; j++) {
+        secp256k1_fe_sqr(&x44, &x44);
+    }
+    secp256k1_fe_mul(&x44, &x44, &x22);
+
+    x88 = x44;
+    for (j=0; j<44; j++) {
+        secp256k1_fe_sqr(&x88, &x88);
+    }
+    secp256k1_fe_mul(&x88, &x88, &x44);
+
+    x176 = x88;
+    for (j=0; j<88; j++) {
+        secp256k1_fe_sqr(&x176, &x176);
+    }
+    secp256k1_fe_mul(&x176, &x176, &x88);
+
+    x220 = x176;
+    for (j=0; j<44; j++) {
+        secp256k1_fe_sqr(&x220, &x220);
+    }
+    secp256k1_fe_mul(&x220, &x220, &x44);
+
+    x223 = x220;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x223, &x223);
+    }
+    secp256k1_fe_mul(&x223, &x223, &x3);
+
+    /* The final result is then assembled using a sliding window over the blocks. */
+
+    t1 = x223;
+    for (j=0; j<23; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, &x22);
+    for (j=0; j<5; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, a);
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, &x2);
+    for (j=0; j<2; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(r, a, &t1);
+}
+
+static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a) {
+#if defined(USE_FIELD_INV_BUILTIN)
+    secp256k1_fe_inv(r, a);
+#elif defined(USE_FIELD_INV_NUM)
+    secp256k1_num n, m;
+    static const secp256k1_fe negone = SECP256K1_FE_CONST(
+        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL,
+        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL, 0xFFFFFC2EUL
+    );
+    /* secp256k1 field prime, value p defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1. */
+    static const unsigned char prime[32] = {
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F
+    };
+    unsigned char b[32];
+    int res;
+    secp256k1_fe c = *a;
+    secp256k1_fe_normalize_var(&c);
+    secp256k1_fe_get_b32(b, &c);
+    secp256k1_num_set_bin(&n, b, 32);
+    secp256k1_num_set_bin(&m, prime, 32);
+    secp256k1_num_mod_inverse(&n, &n, &m);
+    secp256k1_num_get_bin(b, 32, &n);
+    res = secp256k1_fe_set_b32(r, b);
+    (void)res;
+    VERIFY_CHECK(res);
+    /* Verify the result is the (unique) valid inverse using non-GMP code. */
+    secp256k1_fe_mul(&c, &c, r);
+    secp256k1_fe_add(&c, &negone);
+    CHECK(secp256k1_fe_normalizes_to_zero_var(&c));
+#else
+#error "Please select field inverse implementation"
+#endif
+}
+
 #endif /* SECP256K1_FIELD_REPR_IMPL_H */
diff --git a/src/field_5x52_impl.h b/src/field_5x52_impl.h
index 3465ea3247..b564567493 100644
--- a/src/field_5x52_impl.h
+++ b/src/field_5x52_impl.h
@@ -498,4 +498,131 @@ static SECP256K1_INLINE void secp256k1_fe_from_storage(secp256k1_fe *r, const se
 #endif
 }
 
+static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a) {
+    secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
+    int j;
+
+    /** The binary representation of (p - 2) has 5 blocks of 1s, with lengths in
+     *  { 1, 2, 22, 223 }. Use an addition chain to calculate 2^n - 1 for each block:
+     *  [1], [2], 3, 6, 9, 11, [22], 44, 88, 176, 220, [223]
+     */
+
+    secp256k1_fe_sqr(&x2, a);
+    secp256k1_fe_mul(&x2, &x2, a);
+
+    secp256k1_fe_sqr(&x3, &x2);
+    secp256k1_fe_mul(&x3, &x3, a);
+
+    x6 = x3;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x6, &x6);
+    }
+    secp256k1_fe_mul(&x6, &x6, &x3);
+
+    x9 = x6;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x9, &x9);
+    }
+    secp256k1_fe_mul(&x9, &x9, &x3);
+
+    x11 = x9;
+    for (j=0; j<2; j++) {
+        secp256k1_fe_sqr(&x11, &x11);
+    }
+    secp256k1_fe_mul(&x11, &x11, &x2);
+
+    x22 = x11;
+    for (j=0; j<11; j++) {
+        secp256k1_fe_sqr(&x22, &x22);
+    }
+    secp256k1_fe_mul(&x22, &x22, &x11);
+
+    x44 = x22;
+    for (j=0; j<22; j++) {
+        secp256k1_fe_sqr(&x44, &x44);
+    }
+    secp256k1_fe_mul(&x44, &x44, &x22);
+
+    x88 = x44;
+    for (j=0; j<44; j++) {
+        secp256k1_fe_sqr(&x88, &x88);
+    }
+    secp256k1_fe_mul(&x88, &x88, &x44);
+
+    x176 = x88;
+    for (j=0; j<88; j++) {
+        secp256k1_fe_sqr(&x176, &x176);
+    }
+    secp256k1_fe_mul(&x176, &x176, &x88);
+
+    x220 = x176;
+    for (j=0; j<44; j++) {
+        secp256k1_fe_sqr(&x220, &x220);
+    }
+    secp256k1_fe_mul(&x220, &x220, &x44);
+
+    x223 = x220;
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&x223, &x223);
+    }
+    secp256k1_fe_mul(&x223, &x223, &x3);
+
+    /* The final result is then assembled using a sliding window over the blocks. */
+
+    t1 = x223;
+    for (j=0; j<23; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, &x22);
+    for (j=0; j<5; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, a);
+    for (j=0; j<3; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(&t1, &t1, &x2);
+    for (j=0; j<2; j++) {
+        secp256k1_fe_sqr(&t1, &t1);
+    }
+    secp256k1_fe_mul(r, a, &t1);
+}
+
+static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a) {
+#if defined(USE_FIELD_INV_BUILTIN)
+    secp256k1_fe_inv(r, a);
+#elif defined(USE_FIELD_INV_NUM)
+    secp256k1_num n, m;
+    static const secp256k1_fe negone = SECP256K1_FE_CONST(
+        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL,
+        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL, 0xFFFFFC2EUL
+    );
+    /* secp256k1 field prime, value p defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1. */
+    static const unsigned char prime[32] = {
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
+        0xFF,0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F
+    };
+    unsigned char b[32];
+    int res;
+    secp256k1_fe c = *a;
+    secp256k1_fe_normalize_var(&c);
+    secp256k1_fe_get_b32(b, &c);
+    secp256k1_num_set_bin(&n, b, 32);
+    secp256k1_num_set_bin(&m, prime, 32);
+    secp256k1_num_mod_inverse(&n, &n, &m);
+    secp256k1_num_get_bin(b, 32, &n);
+    res = secp256k1_fe_set_b32(r, b);
+    (void)res;
+    VERIFY_CHECK(res);
+    /* Verify the result is the (unique) valid inverse using non-GMP code. */
+    secp256k1_fe_mul(&c, &c, r);
+    secp256k1_fe_add(&c, &negone);
+    CHECK(secp256k1_fe_normalizes_to_zero_var(&c));
+#else
+#error "Please select field inverse implementation"
+#endif
+}
+
 #endif /* SECP256K1_FIELD_REPR_IMPL_H */
diff --git a/src/field_impl.h b/src/field_impl.h
index f0096f6312..7b75e98601 100644
--- a/src/field_impl.h
+++ b/src/field_impl.h
@@ -136,133 +136,6 @@ static int secp256k1_fe_sqrt(secp256k1_fe *r, const secp256k1_fe *a) {
     return secp256k1_fe_equal(&t1, a);
 }
 
-static void secp256k1_fe_inv(secp256k1_fe *r, const secp256k1_fe *a) {
-    secp256k1_fe x2, x3, x6, x9, x11, x22, x44, x88, x176, x220, x223, t1;
-    int j;
-
-    /** The binary representation of (p - 2) has 5 blocks of 1s, with lengths in
-     *  { 1, 2, 22, 223 }. Use an addition chain to calculate 2^n - 1 for each block:
-     *  [1], [2], 3, 6, 9, 11, [22], 44, 88, 176, 220, [223]
-     */
-
-    secp256k1_fe_sqr(&x2, a);
-    secp256k1_fe_mul(&x2, &x2, a);
-
-    secp256k1_fe_sqr(&x3, &x2);
-    secp256k1_fe_mul(&x3, &x3, a);
-
-    x6 = x3;
-    for (j=0; j<3; j++) {
-        secp256k1_fe_sqr(&x6, &x6);
-    }
-    secp256k1_fe_mul(&x6, &x6, &x3);
-
-    x9 = x6;
-    for (j=0; j<3; j++) {
-        secp256k1_fe_sqr(&x9, &x9);
-    }
-    secp256k1_fe_mul(&x9, &x9, &x3);
-
-    x11 = x9;
-    for (j=0; j<2; j++) {
-        secp256k1_fe_sqr(&x11, &x11);
-    }
-    secp256k1_fe_mul(&x11, &x11, &x2);
-
-    x22 = x11;
-    for (j=0; j<11; j++) {
-        secp256k1_fe_sqr(&x22, &x22);
-    }
-    secp256k1_fe_mul(&x22, &x22, &x11);
-
-    x44 = x22;
-    for (j=0; j<22; j++) {
-        secp256k1_fe_sqr(&x44, &x44);
-    }
-    secp256k1_fe_mul(&x44, &x44, &x22);
-
-    x88 = x44;
-    for (j=0; j<44; j++) {
-        secp256k1_fe_sqr(&x88, &x88);
-    }
-    secp256k1_fe_mul(&x88, &x88, &x44);
-
-    x176 = x88;
-    for (j=0; j<88; j++) {
-        secp256k1_fe_sqr(&x176, &x176);
-    }
-    secp256k1_fe_mul(&x176, &x176, &x88);
-
-    x220 = x176;
-    for (j=0; j<44; j++) {
-        secp256k1_fe_sqr(&x220, &x220);
-    }
-    secp256k1_fe_mul(&x220, &x220, &x44);
-
-    x223 = x220;
-    for (j=0; j<3; j++) {
-        secp256k1_fe_sqr(&x223, &x223);
-    }
-    secp256k1_fe_mul(&x223, &x223, &x3);
-
-    /* The final result is then assembled using a sliding window over the blocks. */
-
-    t1 = x223;
-    for (j=0; j<23; j++) {
-        secp256k1_fe_sqr(&t1, &t1);
-    }
-    secp256k1_fe_mul(&t1, &t1, &x22);
-    for (j=0; j<5; j++) {
-        secp256k1_fe_sqr(&t1, &t1);
-    }
-    secp256k1_fe_mul(&t1, &t1, a);
-    for (j=0; j<3; j++) {
-        secp256k1_fe_sqr(&t1, &t1);
-    }
-    secp256k1_fe_mul(&t1, &t1, &x2);
-    for (j=0; j<2; j++) {
-        secp256k1_fe_sqr(&t1, &t1);
-    }
-    secp256k1_fe_mul(r, a, &t1);
-}
-
-static void secp256k1_fe_inv_var(secp256k1_fe *r, const secp256k1_fe *a) {
-#if defined(USE_FIELD_INV_BUILTIN)
-    secp256k1_fe_inv(r, a);
-#elif defined(USE_FIELD_INV_NUM)
-    secp256k1_num n, m;
-    static const secp256k1_fe negone = SECP256K1_FE_CONST(
-        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFFUL,
-        0xFFFFFFFFUL, 0xFFFFFFFFUL, 0xFFFFFFFEUL, 0xFFFFFC2EUL
-    );
-    /* secp256k1 field prime, value p defined in "Standards for Efficient Cryptography" (SEC2) 2.7.1. */
-    static const unsigned char prime[32] = {
-        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
-        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
-        0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
-        0xFF,0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F
-    };
-    unsigned char b[32];
-    int res;
-    secp256k1_fe c = *a;
-    secp256k1_fe_normalize_var(&c);
-    secp256k1_fe_get_b32(b, &c);
-    secp256k1_num_set_bin(&n, b, 32);
-    secp256k1_num_set_bin(&m, prime, 32);
-    secp256k1_num_mod_inverse(&n, &n, &m);
-    secp256k1_num_get_bin(b, 32, &n);
-    res = secp256k1_fe_set_b32(r, b);
-    (void)res;
-    VERIFY_CHECK(res);
-    /* Verify the result is the (unique) valid inverse using non-GMP code. */
-    secp256k1_fe_mul(&c, &c, r);
-    secp256k1_fe_add(&c, &negone);
-    CHECK(secp256k1_fe_normalizes_to_zero_var(&c));
-#else
-#error "Please select field inverse implementation"
-#endif
-}
-
 static int secp256k1_fe_is_quad_var(const secp256k1_fe *a) {
 #ifndef USE_NUM_NONE
     unsigned char b[32];