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 */
fls32(u32 a)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 */
__ffs32(u32 a)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 */
ffz32(u32 a)107 static inline unsigned int ffz32(u32 a)
108 {
109 return ffz(a);
110 }
ffz64(u64 a)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