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/**
41 * min - return minimum of two values of the same or compatible types
42 * @x: first value
43 * @y: second value
44 */
45#define min(x, y) __careful_cmp(x, y, <)
46
47/**
48 * max - return maximum of two values of the same or compatible types
49 * @x: first value
50 * @y: second value
51 */
52#define max(x, y) __careful_cmp(x, y, >)
53
54/**
55 * min3 - return minimum of three values
56 * @x: first value
57 * @y: second value
58 * @z: third value
59 */
60#define min3(x, y, z) min((typeof(x))min(x, y), z)
61
62/**
63 * max3 - return maximum of three values
64 * @x: first value
65 * @y: second value
66 * @z: third value
67 */
68#define max3(x, y, z) max((typeof(x))max(x, y), z)
69
70/**
71 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
72 * @x: value1
73 * @y: value2
74 */
75#define min_not_zero(x, y) ({ \
76 typeof(x) __x = (x); \
77 typeof(y) __y = (y); \
78 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
79
80/**
81 * clamp - return a value clamped to a given range with strict typechecking
82 * @val: current value
83 * @lo: lowest allowable value
84 * @hi: highest allowable value
85 *
86 * This macro does strict typechecking of @lo/@hi to make sure they are of the
87 * same type as @val. See the unnecessary pointer comparisons.
88 */
89#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
90
91/*
92 * ..and if you can't take the strict
93 * types, you can specify one yourself.
94 *
95 * Or not use min/max/clamp at all, of course.
96 */
97
98/**
99 * min_t - return minimum of two values, using the specified type
100 * @type: data type to use
101 * @x: first value
102 * @y: second value
103 */
104#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
105
106/**
107 * max_t - return maximum of two values, using the specified type
108 * @type: data type to use
109 * @x: first value
110 * @y: second value
111 */
112#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
113
114/**
115 * clamp_t - return a value clamped to a given range using a given type
116 * @type: the type of variable to use
117 * @val: current value
118 * @lo: minimum allowable value
119 * @hi: maximum allowable value
120 *
121 * This macro does no typechecking and uses temporary variables of type
122 * @type to make all the comparisons.
123 */
124#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
125
126/**
127 * clamp_val - return a value clamped to a given range using val's type
128 * @val: current value
129 * @lo: minimum allowable value
130 * @hi: maximum allowable value
131 *
132 * This macro does no typechecking and uses temporary variables of whatever
133 * type the input argument @val is. This is useful when @val is an unsigned
134 * type and @lo and @hi are literals that will otherwise be assigned a signed
135 * integer type.
136 */
137#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
138
139/**
140 * swap - swap values of @a and @b
141 * @a: first value
142 * @b: second value
143 */
144#define swap(a, b) \
145 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
146
147#endif /* _LINUX_MINMAX_H */
148

source code of linux/include/linux/minmax.h