kernel / include / linux / minmax.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_MINMAX_H
#define _LINUX_MINMAX_H

#include <linux/const.h>
#include <linux/types.h>

/*
 * min()/max()/clamp() macros must accomplish three things:
 *
 * - avoid multiple evaluations of the arguments (so side-effects like
 *   "x++" happen only once) when non-constant.
 * - perform strict type-checking (to generate warnings instead of
 *   nasty runtime surprises). See the "unnecessary" pointer comparison
 *   in __typecheck().
 * - retain result as a constant expressions when called with only
 *   constant expressions (to avoid tripping VLA warnings in stack
 *   allocation usage).
 */
#define __typecheck(x, y) \
	(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))

#define __no_side_effects(x, y) \
		(__is_constexpr(x) && __is_constexpr(y))

#define __safe_cmp(x, y) \
		(__typecheck(x, y) && __no_side_effects(x, y))

#define __cmp(x, y, op)	((x) op (y) ? (x) : (y))

#define __cmp_once(x, y, unique_x, unique_y, op) ({	\
		typeof(x) unique_x = (x);		\
		typeof(y) unique_y = (y);		\
		__cmp(unique_x, unique_y, op); })

#define __careful_cmp(x, y, op) \
	__builtin_choose_expr(__safe_cmp(x, y), \
		__cmp(x, y, op), \
		__cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))

#define __clamp(val, lo, hi)	\
	((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))

#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({	\
		typeof(val) unique_val = (val);				\
		typeof(lo) unique_lo = (lo);				\
		typeof(hi) unique_hi = (hi);				\
		__clamp(unique_val, unique_lo, unique_hi); })

#define __clamp_input_check(lo, hi)					\
        (BUILD_BUG_ON_ZERO(__builtin_choose_expr(			\
                __is_constexpr((lo) > (hi)), (lo) > (hi), false)))

#define __careful_clamp(val, lo, hi) ({					\
	__clamp_input_check(lo, hi) +					\
	__builtin_choose_expr(__typecheck(val, lo) && __typecheck(val, hi) && \
			      __typecheck(hi, lo) && __is_constexpr(val) && \
			      __is_constexpr(lo) && __is_constexpr(hi),	\
		__clamp(val, lo, hi),					\
		__clamp_once(val, lo, hi, __UNIQUE_ID(__val),		\
			     __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })

/**
 * min - return minimum of two values of the same or compatible types
 * @x: first value
 * @y: second value
 */
#define min(x, y)	__careful_cmp(x, y, <)

/**
 * max - return maximum of two values of the same or compatible types
 * @x: first value
 * @y: second value
 */
#define max(x, y)	__careful_cmp(x, y, >)

/**
 * min3 - return minimum of three values
 * @x: first value
 * @y: second value
 * @z: third value
 */
#define min3(x, y, z) min((typeof(x))min(x, y), z)

/**
 * max3 - return maximum of three values
 * @x: first value
 * @y: second value
 * @z: third value
 */
#define max3(x, y, z) max((typeof(x))max(x, y), z)

/**
 * min_not_zero - return the minimum that is _not_ zero, unless both are zero
 * @x: value1
 * @y: value2
 */
#define min_not_zero(x, y) ({			\
	typeof(x) __x = (x);			\
	typeof(y) __y = (y);			\
	__x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })

/**
 * clamp - return a value clamped to a given range with strict typechecking
 * @val: current value
 * @lo: lowest allowable value
 * @hi: highest allowable value
 *
 * This macro does strict typechecking of @lo/@hi to make sure they are of the
 * same type as @val.  See the unnecessary pointer comparisons.
 */
#define clamp(val, lo, hi) __careful_clamp(val, lo, hi)

/*
 * ..and if you can't take the strict
 * types, you can specify one yourself.
 *
 * Or not use min/max/clamp at all, of course.
 */

/**
 * min_t - return minimum of two values, using the specified type
 * @type: data type to use
 * @x: first value
 * @y: second value
 */
#define min_t(type, x, y)	__careful_cmp((type)(x), (type)(y), <)

/**
 * max_t - return maximum of two values, using the specified type
 * @type: data type to use
 * @x: first value
 * @y: second value
 */
#define max_t(type, x, y)	__careful_cmp((type)(x), (type)(y), >)

/*
 * Remove a const qualifier from integer types
 * _Generic(foo, type-name: association, ..., default: association) performs a
 * comparison against the foo type (not the qualified type).
 * Do not use the const keyword in the type-name as it will not match the
 * unqualified type of foo.
 */
#define __unconst_integer_type_cases(type)	\
	unsigned type:  (unsigned type)0,	\
	signed type:    (signed type)0

#define __unconst_integer_typeof(x) typeof(			\
	_Generic((x),						\
		char: (char)0,					\
		__unconst_integer_type_cases(char),		\
		__unconst_integer_type_cases(short),		\
		__unconst_integer_type_cases(int),		\
		__unconst_integer_type_cases(long),		\
		__unconst_integer_type_cases(long long),	\
		default: (x)))

/*
 * Do not check the array parameter using __must_be_array().
 * In the following legit use-case where the "array" passed is a simple pointer,
 * __must_be_array() will return a failure.
 * --- 8< ---
 * int *buff
 * ...
 * min = min_array(buff, nb_items);
 * --- 8< ---
 *
 * The first typeof(&(array)[0]) is needed in order to support arrays of both
 * 'int *buff' and 'int buff[N]' types.
 *
 * The array can be an array of const items.
 * typeof() keeps the const qualifier. Use __unconst_integer_typeof() in order
 * to discard the const qualifier for the __element variable.
 */
#define __minmax_array(op, array, len) ({				\
	typeof(&(array)[0]) __array = (array);				\
	typeof(len) __len = (len);					\
	__unconst_integer_typeof(__array[0]) __element = __array[--__len]; \
	while (__len--)							\
		__element = op(__element, __array[__len]);		\
	__element; })

/**
 * min_array - return minimum of values present in an array
 * @array: array
 * @len: array length
 *
 * Note that @len must not be zero (empty array).
 */
#define min_array(array, len) __minmax_array(min, array, len)

/**
 * max_array - return maximum of values present in an array
 * @array: array
 * @len: array length
 *
 * Note that @len must not be zero (empty array).
 */
#define max_array(array, len) __minmax_array(max, array, len)

/**
 * clamp_t - return a value clamped to a given range using a given type
 * @type: the type of variable to use
 * @val: current value
 * @lo: minimum allowable value
 * @hi: maximum allowable value
 *
 * This macro does no typechecking and uses temporary variables of type
 * @type to make all the comparisons.
 */
#define clamp_t(type, val, lo, hi) __careful_clamp((type)(val), (type)(lo), (type)(hi))

/**
 * clamp_val - return a value clamped to a given range using val's type
 * @val: current value
 * @lo: minimum allowable value
 * @hi: maximum allowable value
 *
 * This macro does no typechecking and uses temporary variables of whatever
 * type the input argument @val is.  This is useful when @val is an unsigned
 * type and @lo and @hi are literals that will otherwise be assigned a signed
 * integer type.
 */
#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)

static inline bool in_range64(u64 val, u64 start, u64 len)
{
	return (val - start) < len;
}

static inline bool in_range32(u32 val, u32 start, u32 len)
{
	return (val - start) < len;
}

/**
 * in_range - Determine if a value lies within a range.
 * @val: Value to test.
 * @start: First value in range.
 * @len: Number of values in range.
 *
 * This is more efficient than "if (start <= val && val < (start + len))".
 * It also gives a different answer if @start + @len overflows the size of
 * the type by a sufficient amount to encompass @val.  Decide for yourself
 * which behaviour you want, or prove that start + len never overflow.
 * Do not blindly replace one form with the other.
 */
#define in_range(val, start, len)					\
	((sizeof(start) | sizeof(len) | sizeof(val)) <= sizeof(u32) ?	\
		in_range32(val, start, len) : in_range64(val, start, len))

/**
 * swap - swap values of @a and @b
 * @a: first value
 * @b: second value
 */
#define swap(a, b) \
	do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)

#endif	/* _LINUX_MINMAX_H */