From 294b5d46da4ea05bc0df80e4a6b5f46c6ca9c8cb Mon Sep 17 00:00:00 2001
From: Jimmy Song <jaejoon@gmail.com>
Date: Tue, 7 Jun 2016 21:03:48 -0500
Subject: [PATCH] btcec: Add regression tests for field.go.

This adds new tests to the TestNormalize, TestMul, TestAdd2 functions
which trigger an issue with modular reduction that was fixed in the
prevous commit to prevent regressions.
---
 btcec/field_test.go | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/btcec/field_test.go b/btcec/field_test.go
index 39d0ad32..792df78d 100644
--- a/btcec/field_test.go
+++ b/btcec/field_test.go
@@ -233,6 +233,18 @@ func TestNormalize(t *testing.T) {
 			[10]uint32{0xfffffc2f, 0xffffff80, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0x3fffc0},
 			[10]uint32{0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x000000},
 		},
+		// Prime larger than P where both first and second words are larger
+		// than P's first and second words
+		{
+			[10]uint32{0xfffffc30, 0xffffff86, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0x3fffc0},
+			[10]uint32{0x00000001, 0x00000006, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x000000},
+		},
+		// Prime larger than P where only the second word is larger
+		// than P's second words.
+		{
+			[10]uint32{0xfffffc2a, 0xffffff87, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0x3fffc0},
+			[10]uint32{0x03fffffb, 0x00000006, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x00000000, 0x000000},
+		},
 		// 2^256 - 1
 		{
 			[10]uint32{0xffffffff, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0xffffffc0, 0x3fffc0},
@@ -481,6 +493,8 @@ func TestAdd2(t *testing.T) {
 		{"fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2e", "1", "0"},
 		// secp256k1 prime + 1
 		{"fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f", "1", "1"},
+		// close but over the secp256k1 prime
+		{"fffffffffffffffffffffffffffffffffffffffffffffffffffffff000000000", "f1ffff000", "1ffff3d1"},
 		// Random samples.
 		{
 			"ad82b8d1cc136e23e9fd77fe2c7db1fe5a2ecbfcbde59ab3529758334f862d28",
@@ -593,6 +607,12 @@ func TestMul(t *testing.T) {
 		{"1", "0", "0"},
 		{"0", "1", "0"},
 		{"1", "1", "1"},
+		// slightly over prime
+		{
+			"ffffffffffffffffffffffffffffffffffffffffffffffffffffffff1ffff",
+			"1000",
+			"1ffff3d1",
+		},
 		// secp256k1 prime-1 * 2
 		{
 			"fffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2e",