From ac9865791a691094293e08702623c3a1374eeb5f Mon Sep 17 00:00:00 2001
From: Martin Holst Swende <martin@swende.se>
Date: Thu, 8 Jun 2017 23:16:05 +0200
Subject: core/vm, common/math: Add doc about Byte, fix format

---
 common/math/big.go      |  8 ++++----
 common/math/big_test.go | 27 ++++++++++++++++-----------
 2 files changed, 20 insertions(+), 15 deletions(-)

(limited to 'common')

diff --git a/common/math/big.go b/common/math/big.go
index c49d751fa..787278650 100644
--- a/common/math/big.go
+++ b/common/math/big.go
@@ -131,7 +131,7 @@ func PaddedBigBytes(bigint *big.Int, n int) []byte {
 }
 
 // bigEndianByteAt returns the byte at position n,
-// if bigint is considered big-endian.
+// in Big-Endian encoding
 // So n==0 returns the least significant byte
 func bigEndianByteAt(bigint *big.Int, n int) byte {
 	words := bigint.Bits()
@@ -148,9 +148,9 @@ func bigEndianByteAt(bigint *big.Int, n int) byte {
 }
 
 // Byte returns the byte at position n,
-// if bigint is considered little-endian with the supplied padlength.
-// n==0 returns the most significant byte
-// bigint '5', padlength 32, n=31 => 5
+// with the supplied padlength in Little-Endian encoding.
+// n==0 returns the MSB
+// Example: bigint '5', padlength 32, n=31 => 5
 func Byte(bigint *big.Int, padlength, n int) byte {
 	if n >= padlength {
 		return byte(0)
diff --git a/common/math/big_test.go b/common/math/big_test.go
index 7cce7c212..be9810dc8 100644
--- a/common/math/big_test.go
+++ b/common/math/big_test.go
@@ -141,6 +141,7 @@ func BenchmarkPaddedBigBytesLargePadding(b *testing.B) {
 		PaddedBigBytes(bigint, 200)
 	}
 }
+
 func BenchmarkPaddedBigBytesSmallPadding(b *testing.B) {
 	bigint := MustParseBig256("0x18F8F8F1000111000110011100222004330052300000000000000000FEFCF3CC")
 	for i := 0; i < b.N; i++ {
@@ -154,18 +155,21 @@ func BenchmarkPaddedBigBytesSmallOnePadding(b *testing.B) {
 		PaddedBigBytes(bigint, 32)
 	}
 }
+
 func BenchmarkByteAtBrandNew(b *testing.B) {
 	bigint := MustParseBig256("0x18F8F8F1000111000110011100222004330052300000000000000000FEFCF3CC")
 	for i := 0; i < b.N; i++ {
 		bigEndianByteAt(bigint, 15)
 	}
 }
+
 func BenchmarkByteAt(b *testing.B) {
 	bigint := MustParseBig256("0x18F8F8F1000111000110011100222004330052300000000000000000FEFCF3CC")
 	for i := 0; i < b.N; i++ {
 		bigEndianByteAt(bigint, 15)
 	}
 }
+
 func BenchmarkByteAtOld(b *testing.B) {
 
 	bigint := MustParseBig256("0x18F8F8F1000111000110011100222004330052300000000000000000FEFCF3CC")
@@ -207,21 +211,22 @@ func TestU256(t *testing.T) {
 		}
 	}
 }
-func TestLittleEndianByteAt(t *testing.T) {
 
+func TestBigEndianByteAt(t *testing.T) {
 	tests := []struct {
 		x   string
 		y   int
 		exp byte
 	}{
-		{"0", 0, 0x00},
-		{"1", 1, 0x00},
-		{"0", 1, 0x00},
-		//{"1", 0, 0x01},
+		{"00", 0, 0x00},
+		{"01", 1, 0x00},
+		{"00", 1, 0x00},
+		{"01", 0, 0x01},
 		{"0000000000000000000000000000000000000000000000000000000000102030", 0, 0x30},
 		{"0000000000000000000000000000000000000000000000000000000000102030", 1, 0x20},
 		{"ABCDEF0908070605040302010000000000000000000000000000000000000000", 31, 0xAB},
 		{"ABCDEF0908070605040302010000000000000000000000000000000000000000", 32, 0x00},
+		{"ABCDEF0908070605040302010000000000000000000000000000000000000000", 500, 0x00},
 	}
 	for _, test := range tests {
 		v := new(big.Int).SetBytes(common.Hex2Bytes(test.x))
@@ -232,17 +237,16 @@ func TestLittleEndianByteAt(t *testing.T) {
 
 	}
 }
-func TestBigEndianByteAt(t *testing.T) {
-
+func TestLittleEndianByteAt(t *testing.T) {
 	tests := []struct {
 		x   string
 		y   int
 		exp byte
 	}{
-		{"0", 0, 0x00},
-		{"1", 1, 0x00},
-		{"0", 1, 0x00},
-		{"1", 0, 0x00},
+		{"00", 0, 0x00},
+		{"01", 1, 0x00},
+		{"00", 1, 0x00},
+		{"01", 0, 0x00},
 		{"0000000000000000000000000000000000000000000000000000000000102030", 0, 0x00},
 		{"0000000000000000000000000000000000000000000000000000000000102030", 1, 0x00},
 		{"ABCDEF0908070605040302010000000000000000000000000000000000000000", 31, 0x00},
@@ -266,6 +270,7 @@ func TestBigEndianByteAt(t *testing.T) {
 
 	}
 }
+
 func TestS256(t *testing.T) {
 	tests := []struct{ x, y *big.Int }{
 		{x: big.NewInt(0), y: big.NewInt(0)},
-- 
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