github.com/mitghi/x@v0.0.0-20191206171256-71e86edf750d/bit/math.go (about) 1 /* MIT License 2 * 3 * Copyright (c) 2018 Mike Taghavi <mitghi[at]gmail.com> 4 * 5 * Permission is hereby granted, free of charge, to any person obtaining a copy 6 * of this software and associated documentation files (the "Software"), to deal 7 * in the Software without restriction, including without limitation the rights 8 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell 9 * copies of the Software, and to permit persons to whom the Software is 10 * furnished to do so, subject to the following conditions: 11 * The above copyright notice and this permission notice shall be included in all 12 * copies or substantial portions of the Software. 13 * 14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 17 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 18 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 19 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE 20 * SOFTWARE. 21 */ 22 23 package bit 24 25 type blktable []int 26 27 var ( 28 mDeBruijnBitPosition [32]int = [32]int{ 29 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 30 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31, 31 } 32 33 blocks blktable = blktable{ 34 8, 8, 8, 35 16, 32, 64, 36 128, 256, 512, 37 1024, 2048, 4096, 8192, 38 16384, 32768, 65536, 131072, 39 262144, 524288, 1048576, 2097152, 40 4194304, 8388608, 16777216, 41 33554432, 67108864, 134217728, 42 268435456, 536870912, 1073741824, 43 2147483648, 4294967296, 44 } 45 ) 46 47 func (b blktable) bin(num int) int { 48 return int(b.lgb2(uint64(num))) 49 } 50 51 func (b blktable) size(num int) int { 52 return b[int(b.bin(num))] 53 } 54 55 func (b blktable) lgb2(num uint64) int { 56 return mDeBruijnBitPosition[int(uint64(uint32(RoundPrevP2(num)-1)*(uint32)(0x07C4ACDD))>>27)] 57 } 58 59 func (b blktable) nbalgn(num uint64) int { 60 if num == 0 { 61 return blocks[0] 62 } 63 return blocks[b.lgb2(num)] 64 } 65 66 func RoundNextP2(num uint64) uint64 { 67 num-- 68 num |= num >> 1 69 num |= num >> 2 70 num |= num >> 4 71 num |= num >> 8 72 num |= num >> 16 73 num |= num >> 32 74 num++ 75 return num 76 } 77 78 func RoundPrevP2(num uint64) uint64 { 79 num-- 80 num |= num >> 1 81 num |= num >> 2 82 num |= num >> 4 83 num |= num >> 8 84 num |= num >> 16 85 num |= num >> 32 86 num++ 87 return num - (num >> 1) 88 } 89 90 func NAlignBits(num uint64) int { 91 return blocks.nbalgn(num) 92 } 93 94 func Lgb2(num uint64) int { 95 return blocks.lgb2(num) 96 } 97 98 // DEV SECTION 99 100 func findslot(n int, wsize int, capacity int) int { 101 return ((n * wsize) / capacity) / 2 102 }