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7ac756f74b
Using bits.TrailingZeroes instead of iterating over each bit is a small but easy win for the common case of only one or two registers being set. I copied in the implementation for use with pre-1.9 bootstraps. Change-Id: Ieaa768554d7d5239a5617fbf34f1ee0b32ce1de5 Reviewed-on: https://go-review.googlesource.com/92395 Run-TryBot: Heschi Kreinick <heschi@google.com> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: David Chase <drchase@google.com>
24 lines
729 B
Go
24 lines
729 B
Go
// Copyright 2018 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 !go1.9
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package ssa
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const deBruijn64 = 0x03f79d71b4ca8b09
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var deBruijn64tab = [64]byte{
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0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,
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62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,
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63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,
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54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,
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}
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// TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.
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func TrailingZeros64(x uint64) int {
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if x == 0 {
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return 64
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}
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return int(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)])
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}
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