LXR linux/include/linux/minmax.h

   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 */
 154