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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_MINMAX_H
3#define _LINUX_MINMAX_H
4
5/*
6 * min()/max()/clamp() macros must accomplish three things:
7 *
8 * - avoid multiple evaluations of the arguments (so side-effects like
9 * "x++" happen only once) when non-constant.
10 * - perform strict type-checking (to generate warnings instead of
11 * nasty runtime surprises). See the "unnecessary" pointer comparison
12 * in __typecheck().
13 * - retain result as a constant expressions when called with only
14 * constant expressions (to avoid tripping VLA warnings in stack
15 * allocation usage).
16 */
17#define __typecheck(x, y) \
18 (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
19
20/*
21 * This returns a constant expression while determining if an argument is
22 * a constant expression, most importantly without evaluating the argument.
23 * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
24 */
25#define __is_constexpr(x) \
26 (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
27
28#define __no_side_effects(x, y) \
29 (__is_constexpr(x) && __is_constexpr(y))
30
31#define __safe_cmp(x, y) \
32 (__typecheck(x, y) && __no_side_effects(x, y))
33
34#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
35
36#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
37 typeof(x) unique_x = (x); \
38 typeof(y) unique_y = (y); \
39 __cmp(unique_x, unique_y, op); })
40
41#define __careful_cmp(x, y, op) \
42 __builtin_choose_expr(__safe_cmp(x, y), \
43 __cmp(x, y, op), \
44 __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
45
46/**
47 * min - return minimum of two values of the same or compatible types
48 * @x: first value
49 * @y: second value
50 */
51#define min(x, y) __careful_cmp(x, y, <)
52
53/**
54 * max - return maximum of two values of the same or compatible types
55 * @x: first value
56 * @y: second value
57 */
58#define max(x, y) __careful_cmp(x, y, >)
59
60/**
61 * min3 - return minimum of three values
62 * @x: first value
63 * @y: second value
64 * @z: third value
65 */
66#define min3(x, y, z) min((typeof(x))min(x, y), z)
67
68/**
69 * max3 - return maximum of three values
70 * @x: first value
71 * @y: second value
72 * @z: third value
73 */
74#define max3(x, y, z) max((typeof(x))max(x, y), z)
75
76/**
77 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
78 * @x: value1
79 * @y: value2
80 */
81#define min_not_zero(x, y) ({ \
82 typeof(x) __x = (x); \
83 typeof(y) __y = (y); \
84 __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
85
86/**
87 * clamp - return a value clamped to a given range with strict typechecking
88 * @val: current value
89 * @lo: lowest allowable value
90 * @hi: highest allowable value
91 *
92 * This macro does strict typechecking of @lo/@hi to make sure they are of the
93 * same type as @val. See the unnecessary pointer comparisons.
94 */
95#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
96
97/*
98 * ..and if you can't take the strict
99 * types, you can specify one yourself.
100 *
101 * Or not use min/max/clamp at all, of course.
102 */
103
104/**
105 * min_t - return minimum of two values, using the specified type
106 * @type: data type to use
107 * @x: first value
108 * @y: second value
109 */
110#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
111
112/**
113 * max_t - return maximum of two values, using the specified type
114 * @type: data type to use
115 * @x: first value
116 * @y: second value
117 */
118#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
119
120/**
121 * clamp_t - return a value clamped to a given range using a given type
122 * @type: the type of variable to use
123 * @val: current value
124 * @lo: minimum allowable value
125 * @hi: maximum allowable value
126 *
127 * This macro does no typechecking and uses temporary variables of type
128 * @type to make all the comparisons.
129 */
130#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
131
132/**
133 * clamp_val - return a value clamped to a given range using val's type
134 * @val: current value
135 * @lo: minimum allowable value
136 * @hi: maximum allowable value
137 *
138 * This macro does no typechecking and uses temporary variables of whatever
139 * type the input argument @val is. This is useful when @val is an unsigned
140 * type and @lo and @hi are literals that will otherwise be assigned a signed
141 * integer type.
142 */
143#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
144
145/**
146 * swap - swap values of @a and @b
147 * @a: first value
148 * @b: second value
149 */
150#define swap(a, b) \
151 do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
152
153#endif /* _LINUX_MINMAX_H */