1 /* SPDX-License-Identifier: GPL-2.0-only */ 2 /* 3 * Copyright (c) 2024-2025, NVIDIA CORPORATION & AFFILIATES 4 * 5 * Helper macros for working with log2 values 6 * 7 */ 8 #ifndef __GENERIC_PT_LOG2_H 9 #define __GENERIC_PT_LOG2_H 10 #include <linux/bitops.h> 11 #include <linux/limits.h> 12 13 /* Compute a */ 14 #define log2_to_int_t(type, a_lg2) ((type)(((type)1) << (a_lg2))) 15 static_assert(log2_to_int_t(unsigned int, 0) == 1); 16 17 /* Compute a - 1 (aka all low bits set) */ 18 #define log2_to_max_int_t(type, a_lg2) ((type)(log2_to_int_t(type, a_lg2) - 1)) 19 20 /* Compute a / b */ 21 #define log2_div_t(type, a, b_lg2) ((type)(((type)a) >> (b_lg2))) 22 static_assert(log2_div_t(unsigned int, 4, 2) == 1); 23 24 /* 25 * Compute: 26 * a / c == b / c 27 * aka the high bits are equal 28 */ 29 #define log2_div_eq_t(type, a, b, c_lg2) \ 30 (log2_div_t(type, (a) ^ (b), c_lg2) == 0) 31 static_assert(log2_div_eq_t(unsigned int, 1, 1, 2)); 32 33 /* Compute a % b */ 34 #define log2_mod_t(type, a, b_lg2) \ 35 ((type)(((type)a) & log2_to_max_int_t(type, b_lg2))) 36 static_assert(log2_mod_t(unsigned int, 1, 2) == 1); 37 38 /* 39 * Compute: 40 * a % b == b - 1 41 * aka the low bits are all 1s 42 */ 43 #define log2_mod_eq_max_t(type, a, b_lg2) \ 44 (log2_mod_t(type, a, b_lg2) == log2_to_max_int_t(type, b_lg2)) 45 static_assert(log2_mod_eq_max_t(unsigned int, 3, 2)); 46 47 /* 48 * Return a value such that: 49 * a / b == ret / b 50 * ret % b == val 51 * aka set the low bits to val. val must be < b 52 */ 53 #define log2_set_mod_t(type, a, val, b_lg2) \ 54 ((((type)(a)) & (~log2_to_max_int_t(type, b_lg2))) | ((type)(val))) 55 static_assert(log2_set_mod_t(unsigned int, 3, 1, 2) == 1); 56 57 /* Return a value such that: 58 * a / b == ret / b 59 * ret % b == b - 1 60 * aka set the low bits to all 1s 61 */ 62 #define log2_set_mod_max_t(type, a, b_lg2) \ 63 (((type)(a)) | log2_to_max_int_t(type, b_lg2)) 64 static_assert(log2_set_mod_max_t(unsigned int, 2, 2) == 3); 65 66 /* Compute a * b */ 67 #define log2_mul_t(type, a, b_lg2) ((type)(((type)a) << (b_lg2))) 68 static_assert(log2_mul_t(unsigned int, 2, 2) == 8); 69 70 #define _dispatch_sz(type, fn, a) \ 71 (sizeof(type) == 4 ? fn##32((u32)a) : fn##64(a)) 72 73 /* 74 * Return the highest value such that: 75 * fls_t(u32, 0) == 0 76 * fls_t(u3, 1) == 1 77 * a >= log2_to_int(ret - 1) 78 * aka find last set bit 79 */ 80 static inline unsigned int fls32(u32 a) 81 { 82 return fls(a); 83 } 84 #define fls_t(type, a) _dispatch_sz(type, fls, a) 85 86 /* 87 * Return the highest value such that: 88 * ffs_t(u32, 0) == UNDEFINED 89 * ffs_t(u32, 1) == 0 90 * log_mod(a, ret) == 0 91 * aka find first set bit 92 */ 93 static inline unsigned int __ffs32(u32 a) 94 { 95 return __ffs(a); 96 } 97 #define ffs_t(type, a) _dispatch_sz(type, __ffs, a) 98 99 /* 100 * Return the highest value such that: 101 * ffz_t(u32, U32_MAX) == UNDEFINED 102 * ffz_t(u32, 0) == 0 103 * ffz_t(u32, 1) == 1 104 * log_mod(a, ret) == log_to_max_int(ret) 105 * aka find first zero bit 106 */ 107 static inline unsigned int ffz32(u32 a) 108 { 109 return ffz(a); 110 } 111 static inline unsigned int ffz64(u64 a) 112 { 113 if (sizeof(u64) == sizeof(unsigned long)) 114 return ffz(a); 115 116 if ((u32)a == U32_MAX) 117 return ffz32(a >> 32) + 32; 118 return ffz32(a); 119 } 120 #define ffz_t(type, a) _dispatch_sz(type, ffz, a) 121 122 #endif 123