Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_MINMAX_H
3#define _LINUX_MINMAX_H
4
5#include <linux/const.h>
6
7/*
8 * min()/max()/clamp() macros must accomplish three things:
9 *
10 * - avoid multiple evaluations of the arguments (so side-effects like
11 * "x++" happen only once) when non-constant.
12 * - perform strict type-checking (to generate warnings instead of
13 * nasty runtime surprises). See the "unnecessary" pointer comparison
14 * in __typecheck().
15 * - retain result as a constant expressions when called with only
16 * constant expressions (to avoid tripping VLA warnings in stack
17 * allocation usage).
18 */
19#define __typecheck(x, y) \
20 (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
21
22#define __no_side_effects(x, y) \
23 (__is_constexpr(x) && __is_constexpr(y))
24
25#define __safe_cmp(x, y) \
26 (__typecheck(x, y) && __no_side_effects(x, y))
27
28#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
29
30#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
31 typeof(x) unique_x = (x); \
32 typeof(y) unique_y = (y); \
33 __cmp(unique_x, unique_y, op); })
34
35#define __careful_cmp(x, y, op) \
36 __builtin_choose_expr(__safe_cmp(x, y), \
37 __cmp(x, y, op), \
38 __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
39
40#define __clamp(val, lo, hi) \
41 ((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
42
43#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
44 typeof(val) unique_val = (val); \
45 typeof(lo) unique_lo = (lo); \
46 typeof(hi) unique_hi = (hi); \
47 __clamp(unique_val, unique_lo, unique_hi); })
48
49#define __clamp_input_check(lo, hi) \
50 (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
51 __is_constexpr((lo) > (hi)), (lo) > (hi), false)))
52
53#define __careful_clamp(val, lo, hi) ({ \
54 __clamp_input_check(lo, hi) + \
55 __builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \
56 __typecheck(hi, lo) && __is_constexpr(val) && \
57 __is_constexpr(lo) && __is_constexpr(hi), \
58 __clamp(val, lo, hi), \
59 __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
60 __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
61
62/**
63 * min - return minimum of two values of the same or compatible types
64 * @x: first value
65 * @y: second value
66 */
67#define min(x, y) __careful_cmp(x, y, <)
68
69/**
70 * max - return maximum of two values of the same or compatible types
71 * @x: first value
72 * @y: second value
73 */
74#define max(x, y) __careful_cmp(x, y, >)
75
76/**
77 * min3 - return minimum of three values
78 * @x: first value
79 * @y: second value
80 * @z: third value
81 */
82#define min3(x, y, z) min((typeof(x))min(x, y), z)
83
84/**
85 * max3 - return maximum of three values
86 * @x: first value
87 * @y: second value
88 * @z: third value
89 */
90#define max3(x, y, z) max((typeof(x))max(x, y), z)
91
92/**
93 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
94 * @x: value1
95 * @y: value2
96 */
97#define min_not_zero(x, y) ({ \
98 typeof(x) __x = (x); \
99 typeof(y) __y = (y); \
100 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
101
102/**
103 * clamp - return a value clamped to a given range with strict typechecking
104 * @val: current value
105 * @lo: lowest allowable value
106 * @hi: highest allowable value
107 *
108 * This macro does strict typechecking of @lo/@hi to make sure they are of the
109 * same type as @val. See the unnecessary pointer comparisons.
110 */
111#define clamp(val, lo, hi) __careful_clamp(val, lo, hi)
112
113/*
114 * ..and if you can't take the strict
115 * types, you can specify one yourself.
116 *
117 * Or not use min/max/clamp at all, of course.
118 */
119
120/**
121 * min_t - return minimum of two values, using the specified type
122 * @type: data type to use
123 * @x: first value
124 * @y: second value
125 */
126#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
127
128/**
129 * max_t - return maximum of two values, using the specified type
130 * @type: data type to use
131 * @x: first value
132 * @y: second value
133 */
134#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
135
136/**
137 * clamp_t - return a value clamped to a given range using a given type
138 * @type: the type of variable to use
139 * @val: current value
140 * @lo: minimum allowable value
141 * @hi: maximum allowable value
142 *
143 * This macro does no typechecking and uses temporary variables of type
144 * @type to make all the comparisons.
145 */
146#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))
147
148/**
149 * clamp_val - return a value clamped to a given range using val's type
150 * @val: current value
151 * @lo: minimum allowable value
152 * @hi: maximum allowable value
153 *
154 * This macro does no typechecking and uses temporary variables of whatever
155 * type the input argument @val is. This is useful when @val is an unsigned
156 * type and @lo and @hi are literals that will otherwise be assigned a signed
157 * integer type.
158 */
159#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
160
161/**
162 * swap - swap values of @a and @b
163 * @a: first value
164 * @b: second value
165 */
166#define swap(a, b) \
167 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
168
169#endif /* _LINUX_MINMAX_H */