include/linux/minmax.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef _LINUX_MINMAX_H
0003 #define _LINUX_MINMAX_H
0004
0005 #include <linux/const.h>
0006
0007 /*
0008  * min()/max()/clamp() macros must accomplish three things:
0009  *
0010  * - avoid multiple evaluations of the arguments (so side-effects like
0011  *   "x++" happen only once) when non-constant.
0012  * - perform strict type-checking (to generate warnings instead of
0013  *   nasty runtime surprises). See the "unnecessary" pointer comparison
0014  *   in __typecheck().
0015  * - retain result as a constant expressions when called with only
0016  *   constant expressions (to avoid tripping VLA warnings in stack
0017  *   allocation usage).
0018  */
0019 #define __typecheck(x, y) \
0020     (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
0021
0022 #define __no_side_effects(x, y) \
0023         (__is_constexpr(x) && __is_constexpr(y))
0024
0025 #define __safe_cmp(x, y) \
0026         (__typecheck(x, y) && __no_side_effects(x, y))
0027
0028 #define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
0029
0030 #define __cmp_once(x, y, unique_x, unique_y, op) ({ \
0031         typeof(x) unique_x = (x);       \
0032         typeof(y) unique_y = (y);       \
0033         __cmp(unique_x, unique_y, op); })
0034
0035 #define __careful_cmp(x, y, op) \
0036     __builtin_choose_expr(__safe_cmp(x, y), \
0037         __cmp(x, y, op), \
0038         __cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
0039
0040 /**
0041  * min - return minimum of two values of the same or compatible types
0042  * @x: first value
0043  * @y: second value
0044  */
0045 #define min(x, y)   __careful_cmp(x, y, <)
0046
0047 /**
0048  * max - return maximum of two values of the same or compatible types
0049  * @x: first value
0050  * @y: second value
0051  */
0052 #define max(x, y)   __careful_cmp(x, y, >)
0053
0054 /**
0055  * min3 - return minimum of three values
0056  * @x: first value
0057  * @y: second value
0058  * @z: third value
0059  */
0060 #define min3(x, y, z) min((typeof(x))min(x, y), z)
0061
0062 /**
0063  * max3 - return maximum of three values
0064  * @x: first value
0065  * @y: second value
0066  * @z: third value
0067  */
0068 #define max3(x, y, z) max((typeof(x))max(x, y), z)
0069
0070 /**
0071  * min_not_zero - return the minimum that is _not_ zero, unless both are zero
0072  * @x: value1
0073  * @y: value2
0074  */
0075 #define min_not_zero(x, y) ({           \
0076     typeof(x) __x = (x);            \
0077     typeof(y) __y = (y);            \
0078     __x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
0079
0080 /**
0081  * clamp - return a value clamped to a given range with strict typechecking
0082  * @val: current value
0083  * @lo: lowest allowable value
0084  * @hi: highest allowable value
0085  *
0086  * This macro does strict typechecking of @lo/@hi to make sure they are of the
0087  * same type as @val.  See the unnecessary pointer comparisons.
0088  */
0089 #define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
0090
0091 /*
0092  * ..and if you can't take the strict
0093  * types, you can specify one yourself.
0094  *
0095  * Or not use min/max/clamp at all, of course.
0096  */
0097
0098 /**
0099  * min_t - return minimum of two values, using the specified type
0100  * @type: data type to use
0101  * @x: first value
0102  * @y: second value
0103  */
0104 #define min_t(type, x, y)   __careful_cmp((type)(x), (type)(y), <)
0105
0106 /**
0107  * max_t - return maximum of two values, using the specified type
0108  * @type: data type to use
0109  * @x: first value
0110  * @y: second value
0111  */
0112 #define max_t(type, x, y)   __careful_cmp((type)(x), (type)(y), >)
0113
0114 /**
0115  * clamp_t - return a value clamped to a given range using a given type
0116  * @type: the type of variable to use
0117  * @val: current value
0118  * @lo: minimum allowable value
0119  * @hi: maximum allowable value
0120  *
0121  * This macro does no typechecking and uses temporary variables of type
0122  * @type to make all the comparisons.
0123  */
0124 #define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
0125
0126 /**
0127  * clamp_val - return a value clamped to a given range using val's type
0128  * @val: current value
0129  * @lo: minimum allowable value
0130  * @hi: maximum allowable value
0131  *
0132  * This macro does no typechecking and uses temporary variables of whatever
0133  * type the input argument @val is.  This is useful when @val is an unsigned
0134  * type and @lo and @hi are literals that will otherwise be assigned a signed
0135  * integer type.
0136  */
0137 #define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
0138
0139 /**
0140  * swap - swap values of @a and @b
0141  * @a: first value
0142  * @b: second value
0143  */
0144 #define swap(a, b) \
0145     do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
0146
0147 #endif  /* _LINUX_MINMAX_H */