...

# Source file src/math/bits/bits_test.go

## Documentation: math/bits

```  // Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style

package bits

import (
"testing"
"unsafe"
)

func TestUintSize(t *testing.T) {
var x uint
if want := unsafe.Sizeof(x) * 8; UintSize != want {
t.Fatalf("UintSize = %d; want %d", UintSize, want)
}
}

for i := 0; i < 256; i++ {
nlz := tab[i].nlz
for k := 0; k < 64-8; k++ {
x := uint64(i) << uint(k)
if x <= 1<<8-1 {
want := nlz - k + (8 - 8)
if x == 0 {
want = 8
}
if got != want {
t.Fatalf("LeadingZeros8(%#02x) == %d; want %d", x, got, want)
}
}

if x <= 1<<16-1 {
want := nlz - k + (16 - 8)
if x == 0 {
want = 16
}
if got != want {
t.Fatalf("LeadingZeros16(%#04x) == %d; want %d", x, got, want)
}
}

if x <= 1<<32-1 {
want := nlz - k + (32 - 8)
if x == 0 {
want = 32
}
if got != want {
t.Fatalf("LeadingZeros32(%#08x) == %d; want %d", x, got, want)
}
if UintSize == 32 {
if got != want {
t.Fatalf("LeadingZeros(%#08x) == %d; want %d", x, got, want)
}
}
}

if x <= 1<<64-1 {
want := nlz - k + (64 - 8)
if x == 0 {
want = 64
}
if got != want {
t.Fatalf("LeadingZeros64(%#016x) == %d; want %d", x, got, want)
}
if UintSize == 64 {
if got != want {
t.Fatalf("LeadingZeros(%#016x) == %d; want %d", x, got, want)
}
}
}
}
}
}

// Exported (global) variable serving as input for some
// of the benchmarks to ensure side-effect free calls
// are not optimized away.
var Input uint64 = deBruijn64

// Exported (global) variable to store function results
// during benchmarking to ensure side-effect free calls
// are not optimized away.
var Output int

var s int
for i := 0; i < b.N; i++ {
s += LeadingZeros(uint(Input) >> (uint(i) % UintSize))
}
Output = s
}

var s int
for i := 0; i < b.N; i++ {
s += LeadingZeros8(uint8(Input) >> (uint(i) % 8))
}
Output = s
}

var s int
for i := 0; i < b.N; i++ {
s += LeadingZeros16(uint16(Input) >> (uint(i) % 16))
}
Output = s
}

var s int
for i := 0; i < b.N; i++ {
s += LeadingZeros32(uint32(Input) >> (uint(i) % 32))
}
Output = s
}

var s int
for i := 0; i < b.N; i++ {
s += LeadingZeros64(uint64(Input) >> (uint(i) % 64))
}
Output = s
}

func TestTrailingZeros(t *testing.T) {
for i := 0; i < 256; i++ {
ntz := tab[i].ntz
for k := 0; k < 64-8; k++ {
x := uint64(i) << uint(k)
want := ntz + k
if x <= 1<<8-1 {
got := TrailingZeros8(uint8(x))
if x == 0 {
want = 8
}
if got != want {
t.Fatalf("TrailingZeros8(%#02x) == %d; want %d", x, got, want)
}
}

if x <= 1<<16-1 {
got := TrailingZeros16(uint16(x))
if x == 0 {
want = 16
}
if got != want {
t.Fatalf("TrailingZeros16(%#04x) == %d; want %d", x, got, want)
}
}

if x <= 1<<32-1 {
got := TrailingZeros32(uint32(x))
if x == 0 {
want = 32
}
if got != want {
t.Fatalf("TrailingZeros32(%#08x) == %d; want %d", x, got, want)
}
if UintSize == 32 {
got = TrailingZeros(uint(x))
if got != want {
t.Fatalf("TrailingZeros(%#08x) == %d; want %d", x, got, want)
}
}
}

if x <= 1<<64-1 {
got := TrailingZeros64(uint64(x))
if x == 0 {
want = 64
}
if got != want {
t.Fatalf("TrailingZeros64(%#016x) == %d; want %d", x, got, want)
}
if UintSize == 64 {
got = TrailingZeros(uint(x))
if got != want {
t.Fatalf("TrailingZeros(%#016x) == %d; want %d", x, got, want)
}
}
}
}
}
}

func BenchmarkTrailingZeros(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += TrailingZeros(uint(Input) << (uint(i) % UintSize))
}
Output = s
}

func BenchmarkTrailingZeros8(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += TrailingZeros8(uint8(Input) << (uint(i) % 8))
}
Output = s
}

func BenchmarkTrailingZeros16(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += TrailingZeros16(uint16(Input) << (uint(i) % 16))
}
Output = s
}

func BenchmarkTrailingZeros32(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += TrailingZeros32(uint32(Input) << (uint(i) % 32))
}
Output = s
}

func BenchmarkTrailingZeros64(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += TrailingZeros64(uint64(Input) << (uint(i) % 64))
}
Output = s
}

func TestOnesCount(t *testing.T) {
var x uint64
for i := 0; i <= 64; i++ {
testOnesCount(t, x, i)
x = x<<1 | 1
}

for i := 64; i >= 0; i-- {
testOnesCount(t, x, i)
x = x << 1
}

for i := 0; i < 256; i++ {
for k := 0; k < 64-8; k++ {
testOnesCount(t, uint64(i)<<uint(k), tab[i].pop)
}
}
}

func testOnesCount(t *testing.T, x uint64, want int) {
if x <= 1<<8-1 {
got := OnesCount8(uint8(x))
if got != want {
t.Fatalf("OnesCount8(%#02x) == %d; want %d", uint8(x), got, want)
}
}

if x <= 1<<16-1 {
got := OnesCount16(uint16(x))
if got != want {
t.Fatalf("OnesCount16(%#04x) == %d; want %d", uint16(x), got, want)
}
}

if x <= 1<<32-1 {
got := OnesCount32(uint32(x))
if got != want {
t.Fatalf("OnesCount32(%#08x) == %d; want %d", uint32(x), got, want)
}
if UintSize == 32 {
got = OnesCount(uint(x))
if got != want {
t.Fatalf("OnesCount(%#08x) == %d; want %d", uint32(x), got, want)
}
}
}

if x <= 1<<64-1 {
got := OnesCount64(uint64(x))
if got != want {
t.Fatalf("OnesCount64(%#016x) == %d; want %d", x, got, want)
}
if UintSize == 64 {
got = OnesCount(uint(x))
if got != want {
t.Fatalf("OnesCount(%#016x) == %d; want %d", x, got, want)
}
}
}
}

func BenchmarkOnesCount(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += OnesCount(uint(Input))
}
Output = s
}

func BenchmarkOnesCount8(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += OnesCount8(uint8(Input))
}
Output = s
}

func BenchmarkOnesCount16(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += OnesCount16(uint16(Input))
}
Output = s
}

func BenchmarkOnesCount32(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += OnesCount32(uint32(Input))
}
Output = s
}

func BenchmarkOnesCount64(b *testing.B) {
var s int
for i := 0; i < b.N; i++ {
s += OnesCount64(uint64(Input))
}
Output = s
}

func TestRotateLeft(t *testing.T) {
var m uint64 = deBruijn64

for k := uint(0); k < 128; k++ {
x8 := uint8(m)
got8 := RotateLeft8(x8, int(k))
want8 := x8<<(k&0x7) | x8>>(8-k&0x7)
if got8 != want8 {
t.Fatalf("RotateLeft8(%#02x, %d) == %#02x; want %#02x", x8, k, got8, want8)
}
got8 = RotateLeft8(want8, -int(k))
if got8 != x8 {
t.Fatalf("RotateLeft8(%#02x, -%d) == %#02x; want %#02x", want8, k, got8, x8)
}

x16 := uint16(m)
got16 := RotateLeft16(x16, int(k))
want16 := x16<<(k&0xf) | x16>>(16-k&0xf)
if got16 != want16 {
t.Fatalf("RotateLeft16(%#04x, %d) == %#04x; want %#04x", x16, k, got16, want16)
}
got16 = RotateLeft16(want16, -int(k))
if got16 != x16 {
t.Fatalf("RotateLeft16(%#04x, -%d) == %#04x; want %#04x", want16, k, got16, x16)
}

x32 := uint32(m)
got32 := RotateLeft32(x32, int(k))
want32 := x32<<(k&0x1f) | x32>>(32-k&0x1f)
if got32 != want32 {
t.Fatalf("RotateLeft32(%#08x, %d) == %#08x; want %#08x", x32, k, got32, want32)
}
got32 = RotateLeft32(want32, -int(k))
if got32 != x32 {
t.Fatalf("RotateLeft32(%#08x, -%d) == %#08x; want %#08x", want32, k, got32, x32)
}
if UintSize == 32 {
x := uint(m)
got := RotateLeft(x, int(k))
want := x<<(k&0x1f) | x>>(32-k&0x1f)
if got != want {
t.Fatalf("RotateLeft(%#08x, %d) == %#08x; want %#08x", x, k, got, want)
}
got = RotateLeft(want, -int(k))
if got != x {
t.Fatalf("RotateLeft(%#08x, -%d) == %#08x; want %#08x", want, k, got, x)
}
}

x64 := uint64(m)
got64 := RotateLeft64(x64, int(k))
want64 := x64<<(k&0x3f) | x64>>(64-k&0x3f)
if got64 != want64 {
t.Fatalf("RotateLeft64(%#016x, %d) == %#016x; want %#016x", x64, k, got64, want64)
}
got64 = RotateLeft64(want64, -int(k))
if got64 != x64 {
t.Fatalf("RotateLeft64(%#016x, -%d) == %#016x; want %#016x", want64, k, got64, x64)
}
if UintSize == 64 {
x := uint(m)
got := RotateLeft(x, int(k))
want := x<<(k&0x3f) | x>>(64-k&0x3f)
if got != want {
t.Fatalf("RotateLeft(%#016x, %d) == %#016x; want %#016x", x, k, got, want)
}
got = RotateLeft(want, -int(k))
if got != x {
t.Fatalf("RotateLeft(%#08x, -%d) == %#08x; want %#08x", want, k, got, x)
}
}
}
}

func BenchmarkRotateLeft(b *testing.B) {
var s uint
for i := 0; i < b.N; i++ {
s += RotateLeft(uint(Input), i)
}
Output = int(s)
}

func BenchmarkRotateLeft8(b *testing.B) {
var s uint8
for i := 0; i < b.N; i++ {
s += RotateLeft8(uint8(Input), i)
}
Output = int(s)
}

func BenchmarkRotateLeft16(b *testing.B) {
var s uint16
for i := 0; i < b.N; i++ {
s += RotateLeft16(uint16(Input), i)
}
Output = int(s)
}

func BenchmarkRotateLeft32(b *testing.B) {
var s uint32
for i := 0; i < b.N; i++ {
s += RotateLeft32(uint32(Input), i)
}
Output = int(s)
}

func BenchmarkRotateLeft64(b *testing.B) {
var s uint64
for i := 0; i < b.N; i++ {
s += RotateLeft64(uint64(Input), i)
}
Output = int(s)
}

func TestReverse(t *testing.T) {
// test each bit
for i := uint(0); i < 64; i++ {
testReverse(t, uint64(1)<<i, uint64(1)<<(63-i))
}

// test a few patterns
for _, test := range []struct {
x, r uint64
}{
{0, 0},
{0x1, 0x8 << 60},
{0x2, 0x4 << 60},
{0x3, 0xc << 60},
{0x4, 0x2 << 60},
{0x5, 0xa << 60},
{0x6, 0x6 << 60},
{0x7, 0xe << 60},
{0x8, 0x1 << 60},
{0x9, 0x9 << 60},
{0xa, 0x5 << 60},
{0xb, 0xd << 60},
{0xc, 0x3 << 60},
{0xd, 0xb << 60},
{0xe, 0x7 << 60},
{0xf, 0xf << 60},
{0x5686487, 0xe12616a000000000},
{0x0123456789abcdef, 0xf7b3d591e6a2c480},
} {
testReverse(t, test.x, test.r)
testReverse(t, test.r, test.x)
}
}

func testReverse(t *testing.T, x64, want64 uint64) {
x8 := uint8(x64)
got8 := Reverse8(x8)
want8 := uint8(want64 >> (64 - 8))
if got8 != want8 {
t.Fatalf("Reverse8(%#02x) == %#02x; want %#02x", x8, got8, want8)
}

x16 := uint16(x64)
got16 := Reverse16(x16)
want16 := uint16(want64 >> (64 - 16))
if got16 != want16 {
t.Fatalf("Reverse16(%#04x) == %#04x; want %#04x", x16, got16, want16)
}

x32 := uint32(x64)
got32 := Reverse32(x32)
want32 := uint32(want64 >> (64 - 32))
if got32 != want32 {
t.Fatalf("Reverse32(%#08x) == %#08x; want %#08x", x32, got32, want32)
}
if UintSize == 32 {
x := uint(x32)
got := Reverse(x)
want := uint(want32)
if got != want {
t.Fatalf("Reverse(%#08x) == %#08x; want %#08x", x, got, want)
}
}

got64 := Reverse64(x64)
if got64 != want64 {
t.Fatalf("Reverse64(%#016x) == %#016x; want %#016x", x64, got64, want64)
}
if UintSize == 64 {
x := uint(x64)
got := Reverse(x)
want := uint(want64)
if got != want {
t.Fatalf("Reverse(%#08x) == %#016x; want %#016x", x, got, want)
}
}
}

func BenchmarkReverse(b *testing.B) {
var s uint
for i := 0; i < b.N; i++ {
s += Reverse(uint(i))
}
Output = int(s)
}

func BenchmarkReverse8(b *testing.B) {
var s uint8
for i := 0; i < b.N; i++ {
s += Reverse8(uint8(i))
}
Output = int(s)
}

func BenchmarkReverse16(b *testing.B) {
var s uint16
for i := 0; i < b.N; i++ {
s += Reverse16(uint16(i))
}
Output = int(s)
}

func BenchmarkReverse32(b *testing.B) {
var s uint32
for i := 0; i < b.N; i++ {
s += Reverse32(uint32(i))
}
Output = int(s)
}

func BenchmarkReverse64(b *testing.B) {
var s uint64
for i := 0; i < b.N; i++ {
s += Reverse64(uint64(i))
}
Output = int(s)
}

func TestReverseBytes(t *testing.T) {
for _, test := range []struct {
x, r uint64
}{
{0, 0},
{0x01, 0x01 << 56},
{0x0123, 0x2301 << 48},
{0x012345, 0x452301 << 40},
{0x01234567, 0x67452301 << 32},
{0x0123456789, 0x8967452301 << 24},
{0x0123456789ab, 0xab8967452301 << 16},
{0x0123456789abcd, 0xcdab8967452301 << 8},
{0x0123456789abcdef, 0xefcdab8967452301 << 0},
} {
testReverseBytes(t, test.x, test.r)
testReverseBytes(t, test.r, test.x)
}
}

func testReverseBytes(t *testing.T, x64, want64 uint64) {
x16 := uint16(x64)
got16 := ReverseBytes16(x16)
want16 := uint16(want64 >> (64 - 16))
if got16 != want16 {
t.Fatalf("ReverseBytes16(%#04x) == %#04x; want %#04x", x16, got16, want16)
}

x32 := uint32(x64)
got32 := ReverseBytes32(x32)
want32 := uint32(want64 >> (64 - 32))
if got32 != want32 {
t.Fatalf("ReverseBytes32(%#08x) == %#08x; want %#08x", x32, got32, want32)
}
if UintSize == 32 {
x := uint(x32)
got := ReverseBytes(x)
want := uint(want32)
if got != want {
t.Fatalf("ReverseBytes(%#08x) == %#08x; want %#08x", x, got, want)
}
}

got64 := ReverseBytes64(x64)
if got64 != want64 {
t.Fatalf("ReverseBytes64(%#016x) == %#016x; want %#016x", x64, got64, want64)
}
if UintSize == 64 {
x := uint(x64)
got := ReverseBytes(x)
want := uint(want64)
if got != want {
t.Fatalf("ReverseBytes(%#016x) == %#016x; want %#016x", x, got, want)
}
}
}

func BenchmarkReverseBytes(b *testing.B) {
var s uint
for i := 0; i < b.N; i++ {
s += ReverseBytes(uint(i))
}
Output = int(s)
}

func BenchmarkReverseBytes16(b *testing.B) {
var s uint16
for i := 0; i < b.N; i++ {
s += ReverseBytes16(uint16(i))
}
Output = int(s)
}

func BenchmarkReverseBytes32(b *testing.B) {
var s uint32
for i := 0; i < b.N; i++ {
s += ReverseBytes32(uint32(i))
}
Output = int(s)
}

func BenchmarkReverseBytes64(b *testing.B) {
var s uint64
for i := 0; i < b.N; i++ {
s += ReverseBytes64(uint64(i))
}
Output = int(s)
}

func TestLen(t *testing.T) {
for i := 0; i < 256; i++ {
len := 8 - tab[i].nlz
for k := 0; k < 64-8; k++ {
x := uint64(i) << uint(k)
want := 0
if x != 0 {
want = len + k
}
if x <= 1<<8-1 {
got := Len8(uint8(x))
if got != want {
t.Fatalf("Len8(%#02x) == %d; want %d", x, got, want)
}
}

if x <= 1<<16-1 {
got := Len16(uint16(x))
if got != want {
t.Fatalf("Len16(%#04x) == %d; want %d", x, got, want)
}
}

if x <= 1<<32-1 {
got := Len32(uint32(x))
if got != want {
t.Fatalf("Len32(%#08x) == %d; want %d", x, got, want)
}
if UintSize == 32 {
got := Len(uint(x))
if got != want {
t.Fatalf("Len(%#08x) == %d; want %d", x, got, want)
}
}
}

if x <= 1<<64-1 {
got := Len64(uint64(x))
if got != want {
t.Fatalf("Len64(%#016x) == %d; want %d", x, got, want)
}
if UintSize == 64 {
got := Len(uint(x))
if got != want {
t.Fatalf("Len(%#016x) == %d; want %d", x, got, want)
}
}
}
}
}
}

// ----------------------------------------------------------------------------
// Testing support

type entry = struct {
nlz, ntz, pop int
}

// tab contains results for all uint8 values
var tab [256]entry

func init() {
tab[0] = entry{8, 8, 0}
for i := 1; i < len(tab); i++ {
// nlz
x := i // x != 0
n := 0
for x&0x80 == 0 {
n++
x <<= 1
}
tab[i].nlz = n

// ntz
x = i // x != 0
n = 0
for x&1 == 0 {
n++
x >>= 1
}
tab[i].ntz = n

// pop
x = i // x != 0
n = 0
for x != 0 {
n += int(x & 1)
x >>= 1
}
tab[i].pop = n
}
}

```

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