gopkg.in/alecthomas/gometalinter.v3@v3.0.0/_linters/src/golang.org/x/tools/container/intsets/popcnt_generic.go (about) 1 // Copyright 2015 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // +build !amd64 appengine 6 // +build !gccgo 7 8 package intsets 9 10 import "runtime" 11 12 // We compared three algorithms---Hacker's Delight, table lookup, 13 // and AMD64's SSE4.1 hardware POPCNT---on a 2.67GHz Xeon X5550. 14 // 15 // % GOARCH=amd64 go test -run=NONE -bench=Popcount 16 // POPCNT 5.12 ns/op 17 // Table 8.53 ns/op 18 // HackersDelight 9.96 ns/op 19 // 20 // % GOARCH=386 go test -run=NONE -bench=Popcount 21 // Table 10.4 ns/op 22 // HackersDelight 5.23 ns/op 23 // 24 // (AMD64's ABM1 hardware supports ntz and nlz too, 25 // but they aren't critical.) 26 27 // popcount returns the population count (number of set bits) of x. 28 func popcount(x word) int { 29 if runtime.GOARCH == "386" { 30 return popcountHD(uint32(x)) 31 } 32 return popcountTable(x) 33 }