1 /* 2 * Copyright 2016 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 * 7 */ 8 9 #ifdef _MSC_VER 10 11 #include <intrin.h> 12 13 #else 14 15 16 17 #endif 18 19 // 20 // 21 // 22 23 #include "util.h" 24 25 // 26 // 27 // 28 29 bool is_pow2_u32(uint32_t n)30is_pow2_u32(uint32_t n) 31 { 32 return (n & (n-1)) == 0; 33 } 34 35 // 36 // 37 // 38 39 uint32_t pow2_ru_u32(uint32_t n)40pow2_ru_u32(uint32_t n) 41 { 42 n--; 43 n |= n >> 1; 44 n |= n >> 2; 45 n |= n >> 4; 46 n |= n >> 8; 47 n |= n >> 16; 48 n++; 49 50 return n; 51 } 52 53 // 54 // 55 // 56 57 uint32_t pow2_rd_u32(uint32_t n)58pow2_rd_u32(uint32_t n) 59 { 60 return 1u << msb_idx_u32(n); 61 } 62 63 // 64 // ASSUMES NON-ZERO 65 // 66 67 uint32_t msb_idx_u32(uint32_t n)68msb_idx_u32(uint32_t n) 69 { 70 #if defined( _MSC_VER ) 71 72 uint32_t index; 73 74 _BitScanReverse((unsigned long *)&index,n); 75 76 return index; 77 78 #elif defined( __GNUC__ ) 79 80 return __builtin_clz(n) ^ 31; 81 82 #else 83 84 #error "No msb_index()" 85 86 #endif 87 } 88 89 // 90 // 91 // 92