зеркало из https://github.com/golang/tools.git
34 строки
927 B
Go
34 строки
927 B
Go
// Copyright 2015 The Go Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style
|
|
// license that can be found in the LICENSE file.
|
|
|
|
// +build !amd64 appengine
|
|
// +build !gccgo
|
|
|
|
package intsets
|
|
|
|
import "runtime"
|
|
|
|
// We compared three algorithms---Hacker's Delight, table lookup,
|
|
// and AMD64's SSE4.1 hardware POPCNT---on a 2.67GHz Xeon X5550.
|
|
//
|
|
// % GOARCH=amd64 go test -run=NONE -bench=Popcount
|
|
// POPCNT 5.12 ns/op
|
|
// Table 8.53 ns/op
|
|
// HackersDelight 9.96 ns/op
|
|
//
|
|
// % GOARCH=386 go test -run=NONE -bench=Popcount
|
|
// Table 10.4 ns/op
|
|
// HackersDelight 5.23 ns/op
|
|
//
|
|
// (AMD64's ABM1 hardware supports ntz and nlz too,
|
|
// but they aren't critical.)
|
|
|
|
// popcount returns the population count (number of set bits) of x.
|
|
func popcount(x word) int {
|
|
if runtime.GOARCH == "386" {
|
|
return popcountHD(uint32(x))
|
|
}
|
|
return popcountTable(x)
|
|
}
|