1 | /* SPDX-License-Identifier: GPL-2.0 */ |
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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 |