| // 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 |
| |
| 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 = 0x077CB531 |
| |
| var 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 = 0x03f79d71b4ca8b09 |
| |
| const 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 TrailingZeros32(x uint32) int { |
| if x == 0 { |
| return 32 |
| } |
| // see comment in TrailingZeros64 |
| return int(deBruijn32tab[(x&-x)*deBruijn32>>(32-5)]) |
| } |
| |
| // TrailingZeros64 returns the number of trailing zero bits in x; the result is 64 for x == 0. |
| func TrailingZeros64(x uint64) int { |
| if x == 0 { |
| return 64 |
| } |
| // 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) |
| return int(deBruijn64tab[(x&-x)*deBruijn64>>(64-6)]) |
| } |
| |
| // TrailingZeros8 returns the number of trailing zero bits in x; the result is 8 for x == 0. |
| func TrailingZeros8(x uint8) int { |
| return int(ntz8tab[x]) |
| } |
| |
| // Bswap64 returns its input with byte order reversed |
| // 0x0102030405060708 -> 0x0807060504030201 |
| func Bswap64(x uint64) uint64 { |
| c8 := uint64(0x00ff00ff00ff00ff) |
| a := x >> 8 & c8 |
| b := (x & c8) << 8 |
| x = a | b |
| c16 := uint64(0x0000ffff0000ffff) |
| a = x >> 16 & c16 |
| b = (x & c16) << 16 |
| x = a | b |
| c32 := uint64(0x00000000ffffffff) |
| a = x >> 32 & c32 |
| b = (x & c32) << 32 |
| x = a | b |
| return x |
| } |
| |
| // Bswap32 returns its input with byte order reversed |
| // 0x01020304 -> 0x04030201 |
| func Bswap32(x uint32) uint32 { |
| c8 := uint32(0x00ff00ff) |
| a := x >> 8 & c8 |
| b := (x & c8) << 8 |
| x = a | b |
| c16 := uint32(0x0000ffff) |
| a = x >> 16 & c16 |
| b = (x & c16) << 16 |
| x = a | b |
| return x |
| } |