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