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 */