// 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.package sys// Copied from math/bits to avoid dependence.var deBruijn32tab = [32]byte{0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9,}const deBruijn32 = 0x077CB531var deBruijn64tab = [64]byte{0, 1, 56, 2, 57, 49, 28, 3, 61, 58, 42, 50, 38, 29, 17, 4,62, 47, 59, 36, 45, 43, 51, 22, 53, 39, 33, 30, 24, 18, 12, 5,63, 55, 48, 27, 60, 41, 37, 16, 46, 35, 44, 21, 52, 32, 23, 11,54, 26, 40, 15, 34, 20, 31, 10, 25, 14, 19, 9, 13, 8, 7, 6,}const deBruijn64 = 0x03f79d71b4ca8b09const ntz8tab = "" +"\x08\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x06\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x07\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x06\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x05\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00" +"\x04\x00\x01\x00\x02\x00\x01\x00\x03\x00\x01\x00\x02\x00\x01\x00"// TrailingZeros32 returns the number of trailing zero bits in x; the result is 32 for x == 0.func ( uint32) int {if == 0 {return32 }// see comment in TrailingZeros64returnint(deBruijn32tab[(&-)*deBruijn32>>(32-5)])}// TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0.func ( uint64) int {if == 0 {return64 }// If popcount is fast, replace code below with return popcount(^x & (x - 1)). // // x & -x leaves only the right-most bit set in the word. Let k be the // index of that bit. Since only a single bit is set, the value is two // to the power of k. Multiplying by a power of two is equivalent to // left shifting, in this case by k bits. The de Bruijn (64 bit) constant // is such that all six bit, consecutive substrings are distinct. // Therefore, if we have a left shifted version of this constant we can // find by how many bits it was shifted by looking at which six bit // substring ended up at the top of the word. // (Knuth, volume 4, section 7.3.1)returnint(deBruijn64tab[(&-)*deBruijn64>>(64-6)])}// TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0.func ( uint8) int {returnint(ntz8tab[])}const len8tab = "" +"\x00\x01\x02\x02\x03\x03\x03\x03\x04\x04\x04\x04\x04\x04\x04\x04" +"\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05\x05" +"\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06" +"\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06\x06" +"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +"\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07\x07" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08" +"\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08\x08"// Len64 returns the minimum number of bits required to represent x; the result is 0 for x == 0.//// nosplit because this is used in src/runtime/histogram.go, which make run in sensitive contexts.////go:nosplitfunc ( uint64) ( int) {if >= 1<<32 { >>= 32 = 32 }if >= 1<<16 { >>= 16 += 16 }if >= 1<<8 { >>= 8 += 8 }return + int(len8tab[])}// --- OnesCount ---const m0 = 0x5555555555555555// 01010101 ...const m1 = 0x3333333333333333// 00110011 ...const m2 = 0x0f0f0f0f0f0f0f0f// 00001111 ...// OnesCount64 returns the number of one bits ("population count") in x.func ( uint64) int {// Implementation: Parallel summing of adjacent bits. // See "Hacker's Delight", Chap. 5: Counting Bits. // The following pattern shows the general approach: // // x = x>>1&(m0&m) + x&(m0&m) // x = x>>2&(m1&m) + x&(m1&m) // x = x>>4&(m2&m) + x&(m2&m) // x = x>>8&(m3&m) + x&(m3&m) // x = x>>16&(m4&m) + x&(m4&m) // x = x>>32&(m5&m) + x&(m5&m) // return int(x) // // Masking (& operations) can be left away when there's no // danger that a field's sum will carry over into the next // field: Since the result cannot be > 64, 8 bits is enough // and we can ignore the masks for the shifts by 8 and up. // Per "Hacker's Delight", the first line can be simplified // more, but it saves at best one instruction, so we leave // it alone for clarity.const = 1<<64 - 1 = >>1&(m0&) + &(m0&) = >>2&(m1&) + &(m1&) = (>>4 + ) & (m2 & ) += >> 8 += >> 16 += >> 32returnint() & (1<<7 - 1)}// LeadingZeros64 returns the number of leading zero bits in x; the result is 64 for x == 0.func ( uint64) int { return64 - Len64() }// LeadingZeros8 returns the number of leading zero bits in x; the result is 8 for x == 0.func ( uint8) int { return8 - Len8() }// Len8 returns the minimum number of bits required to represent x; the result is 0 for x == 0.func ( uint8) int {returnint(len8tab[])}// 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}// Prefetch prefetches data from memory addr to cache//// AMD64: Produce PREFETCHT0 instruction//// ARM64: Produce PRFM instruction with PLDL1KEEP optionfunc ( uintptr) {}// PrefetchStreamed prefetches data from memory addr, with a hint that this data is being streamed.// That is, it is likely to be accessed very soon, but only once. If possible, this will avoid polluting the cache.//// AMD64: Produce PREFETCHNTA instruction//// ARM64: Produce PRFM instruction with PLDL1STRM optionfunc ( uintptr) {}
The pages are generated with Goldsv0.6.9-preview. (GOOS=linux GOARCH=amd64)
Golds is a Go 101 project developed by Tapir Liu.
PR and bug reports are welcome and can be submitted to the issue list.
Please follow @Go100and1 (reachable from the left QR code) to get the latest news of Golds.