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https://github.com/golang/go
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b7f0150d16
This function accounts for 2% of "godoc -analysis=pointer" and this change makes it twice as fast---and simpler. Added test and benchmark. Change-Id: I8578fa42dce34df057d81f6c522a7b4e0506d09d Reviewed-on: https://go-review.googlesource.com/15211 Run-TryBot: Robert Griesemer <gri@golang.org> Reviewed-by: Ilya Tocar <ilya.tocar@intel.com> Reviewed-by: Robert Griesemer <gri@golang.org>
33 lines
900 B
Go
33 lines
900 B
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !amd64
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package intsets
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import "runtime"
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// We compared three algorithms---Hacker's Delight, table lookup,
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// and AMD64's SSE4.1 hardware POPCNT---on a 2.67GHz Xeon X5550.
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//
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// % GOARCH=amd64 go test -run=NONE -bench=Popcount
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// POPCNT 5.12 ns/op
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// Table 8.53 ns/op
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// HackersDelight 9.96 ns/op
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//
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// % GOARCH=386 go test -run=NONE -bench=Popcount
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// Table 10.4 ns/op
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// HackersDelight 5.23 ns/op
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//
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// (AMD64's ABM1 hardware supports ntz and nlz too,
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// but they aren't critical.)
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// popcount returns the population count (number of set bits) of x.
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func popcount(x word) int {
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if runtime.GOARCH == "386" {
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return popcountHD(uint32(x))
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}
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return popcountTable(x)
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}
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