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