gopl.io/ch2/popcount/popcount_test.go

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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
package popcount_test
import (
"testing"
"gopl.io/ch2/popcount"
)
// -- Alternative implementations --
func BitCount(x uint64) int {
// Hacker's Delight, Figure 5-2.
x = x - ((x >> 1) & 0x5555555555555555)
x = (x & 0x3333333333333333) + ((x >> 2) & 0x3333333333333333)
x = (x + (x >> 4)) & 0x0f0f0f0f0f0f0f0f
x = x + (x >> 8)
x = x + (x >> 16)
x = x + (x >> 32)
return int(x & 0x7f)
}
func PopCountByClearing(x uint64) int {
n := 0
for x != 0 {
x = x & (x - 1) // clear rightmost non-zero bit
n++
}
return n
}
func PopCountByShifting(x uint64) int {
n := 0
for i := uint(0); i < 64; i++ {
if x&(1<<i) != 0 {
n++
}
}
return n
}
// -- Benchmarks --
func BenchmarkPopCount(b *testing.B) {
for i := 0; i < b.N; i++ {
popcount.PopCount(0x1234567890ABCDEF)
}
}
func BenchmarkBitCount(b *testing.B) {
for i := 0; i < b.N; i++ {
BitCount(0x1234567890ABCDEF)
}
}
func BenchmarkPopCountByClearing(b *testing.B) {
for i := 0; i < b.N; i++ {
PopCountByClearing(0x1234567890ABCDEF)
}
}
func BenchmarkPopCountByShifting(b *testing.B) {
for i := 0; i < b.N; i++ {
PopCountByShifting(0x1234567890ABCDEF)
}
}
// 2.67GHz Xeon
// $ go test -cpu=4 -bench=. gopl.io/ch2/popcount
// BenchmarkPopCount-4 200000000 6.30 ns/op
// BenchmarkBitCount-4 300000000 4.15 ns/op
// BenchmarkPopCountByClearing-4 30000000 45.2 ns/op
// BenchmarkPopCountByShifting-4 10000000 153 ns/op
//
// 2.5GHz Intel Core i5
// $ go test -cpu=4 -bench=. gopl.io/ch2/popcount
// testing: warning: no tests to run
// BenchmarkPopCount-4 200000000 7.52 ns/op
// BenchmarkBitCount-4 500000000 3.36 ns/op
// BenchmarkPopCountByClearing-4 50000000 34.3 ns/op
// BenchmarkPopCountByShifting-4 20000000 108 ns/op