math/bits: faster Rotate functions, added respective benchmarks

Measured on 2.3 GHz Intel Core i7, running maxOS 10.12.3.

benchmark                    old ns/op     new ns/op     delta
BenchmarkRotateLeft-8        7.87          7.00          -11.05%
BenchmarkRotateLeft8-8       8.41          4.52          -46.25%
BenchmarkRotateLeft16-8      8.07          4.55          -43.62%
BenchmarkRotateLeft32-8      8.36          4.73          -43.42%
BenchmarkRotateLeft64-8      7.93          4.78          -39.72%

BenchmarkRotateRight-8       8.23          6.72          -18.35%
BenchmarkRotateRight8-8      8.76          4.39          -49.89%
BenchmarkRotateRight16-8     9.07          4.44          -51.05%
BenchmarkRotateRight32-8     8.85          4.46          -49.60%
BenchmarkRotateRight64-8     8.11          4.43          -45.38%

Change-Id: I79ea1e9e6fc65f95794a91f860a911efed3aa8a1
Reviewed-on: https://go-review.googlesource.com/37219
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

1 files changed, 80 insertions, 0 deletions

diff --git a/src/math/bits/bits_test.go b/src/math/bits/bits_test.go
index b268b0a004..20b0b63fff 100644
--- a/src/math/bits/bits_test.go
+++ b/src/math/bits/bits_test.go
@@ -289,6 +289,46 @@ func TestRotateLeft(t *testing.T) {
 	}
 }
 
+func BenchmarkRotateLeft(b *testing.B) {
+	var s uint
+	for i := 0; i < b.N; i++ {
+		s += RotateLeft(uint(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateLeft8(b *testing.B) {
+	var s uint8
+	for i := 0; i < b.N; i++ {
+		s += RotateLeft8(uint8(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateLeft16(b *testing.B) {
+	var s uint16
+	for i := 0; i < b.N; i++ {
+		s += RotateLeft16(uint16(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateLeft32(b *testing.B) {
+	var s uint32
+	for i := 0; i < b.N; i++ {
+		s += RotateLeft32(uint32(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateLeft64(b *testing.B) {
+	var s uint64
+	for i := 0; i < b.N; i++ {
+		s += RotateLeft64(uint64(Input), i)
+	}
+	Unused = int(s)
+}
+
 func TestRotateRight(t *testing.T) {
 	var m uint64 = deBruijn64
 
@@ -339,6 +379,46 @@ func TestRotateRight(t *testing.T) {
 	}
 }
 
+func BenchmarkRotateRight(b *testing.B) {
+	var s uint
+	for i := 0; i < b.N; i++ {
+		s += RotateRight(uint(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateRight8(b *testing.B) {
+	var s uint8
+	for i := 0; i < b.N; i++ {
+		s += RotateRight8(uint8(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateRight16(b *testing.B) {
+	var s uint16
+	for i := 0; i < b.N; i++ {
+		s += RotateRight16(uint16(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateRight32(b *testing.B) {
+	var s uint32
+	for i := 0; i < b.N; i++ {
+		s += RotateRight32(uint32(Input), i)
+	}
+	Unused = int(s)
+}
+
+func BenchmarkRotateRight64(b *testing.B) {
+	var s uint64
+	for i := 0; i < b.N; i++ {
+		s += RotateRight64(uint64(Input), i)
+	}
+	Unused = int(s)
+}
+
 func TestReverse(t *testing.T) {
 	// test each bit
 	for i := uint(0); i < 64; i++ {