// Copyright 2016 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.//go:build !386// TODO finish intrinsifying 386, deadcode the assembly, remove build tags, merge w/ intrinsics_common// TODO replace all uses of CtzXX with TrailingZerosXX; they are the same.package sys// Using techniques from http://supertech.csail.mit.edu/papers/debruijn.pdfconst deBruijn64ctz = 0x0218a392cd3d5dbfvar deBruijnIdx64ctz = [64]byte{0, 1, 2, 7, 3, 13, 8, 19,4, 25, 14, 28, 9, 34, 20, 40,5, 17, 26, 38, 15, 46, 29, 48,10, 31, 35, 54, 21, 50, 41, 57,63, 6, 12, 18, 24, 27, 33, 39,16, 37, 45, 47, 30, 53, 49, 56,62, 11, 23, 32, 36, 44, 52, 55,61, 22, 43, 51, 60, 42, 59, 58,}const deBruijn32ctz = 0x04653adfvar deBruijnIdx32ctz = [32]byte{0, 1, 2, 6, 3, 11, 7, 16,4, 14, 12, 21, 8, 23, 17, 26,31, 5, 10, 15, 13, 20, 22, 25,30, 9, 19, 24, 29, 18, 28, 27,}// Ctz64 counts trailing (low-order) zeroes,// and if all are zero, then 64.func ( uint64) int { &= - // isolate low-order bit := * deBruijn64ctz >> 58// extract part of deBruijn sequence := int(deBruijnIdx64ctz[]) // convert to bit index := int(( - 1) >> 57 & 64) // adjustment if zeroreturn + }// Ctz32 counts trailing (low-order) zeroes,// and if all are zero, then 32.func ( uint32) int { &= - // isolate low-order bit := * deBruijn32ctz >> 27// extract part of deBruijn sequence := int(deBruijnIdx32ctz[]) // convert to bit index := int(( - 1) >> 26 & 32) // adjustment if zeroreturn + }// Ctz8 returns the number of trailing zero bits in x; the result is 8 for x == 0.func ( uint8) int {returnint(ntz8tab[])}// Bswap64 returns its input with byte order reversed// 0x0102030405060708 -> 0x0807060504030201func ( uint64) uint64 { := uint64(0x00ff00ff00ff00ff) := >> 8 & := ( & ) << 8 = | := uint64(0x0000ffff0000ffff) = >> 16 & = ( & ) << 16 = | := uint64(0x00000000ffffffff) = >> 32 & = ( & ) << 32 = | return}// Bswap32 returns its input with byte order reversed// 0x01020304 -> 0x04030201func ( uint32) uint32 { := uint32(0x00ff00ff) := >> 8 & := ( & ) << 8 = | := uint32(0x0000ffff) = >> 16 & = ( & ) << 16 = | return}
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