minmax.h
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_MINMAX_H
#define _LINUX_MINMAX_H
#include <linux/build_bug.h>
#include <linux/compiler.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.
* - Retain result as a constant expressions when called with only
* constant expressions (to avoid tripping VLA warnings in stack
* allocation usage).
* - Perform signed v unsigned type-checking (to generate compile
* errors instead of nasty runtime surprises).
* - Unsigned char/short are always promoted to signed int and can be
* compared against signed or unsigned arguments.
* - Unsigned arguments can be compared against non-negative signed constants.
* - Comparison of a signed argument against an unsigned constant fails
* even if the constant is below __INT_MAX__ and could be cast to int.
*/
#define __typecheck(x, y) \
(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
/* is_signed_type() isn't a constexpr for pointer types */
#define __is_signed(x) \
__builtin_choose_expr(__is_constexpr(is_signed_type(typeof(x))), \
is_signed_type(typeof(x)), 0)
/* True for a non-negative signed int constant */
#define __is_noneg_int(x) \
(__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
#define __types_ok(x, y) \
(__is_signed(x) == __is_signed(y) || \
__is_signed((x) + 0) == __is_signed((y) + 0) || \
__is_noneg_int(x) || __is_noneg_int(y))
#define __cmp_op_min <
#define __cmp_op_max >
#define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y))
#define __cmp_once(op, x, y, unique_x, unique_y) ({ \
typeof(x) unique_x = (x); \
typeof(y) unique_y = (y); \
static_assert(__types_ok(x, y), \
#op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
__cmp(op, unique_x, unique_y); })
#define __careful_cmp(op, x, y) \
__builtin_choose_expr(__is_constexpr((x) - (y)), \
__cmp(op, x, y), \
__cmp_once(op, x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y)))
#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); \
static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
(lo) <= (hi), true), \
"clamp() low limit " #lo " greater than high limit " #hi); \
static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
__clamp(unique_val, unique_lo, unique_hi); })
#define __careful_clamp(val, lo, hi) ({ \
__builtin_choose_expr(__is_constexpr((val) - (lo) + (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(min, 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(max, x, y)
/**
* umin - return minimum of two non-negative values
* Signed types are zero extended to match a larger unsigned type.
* @x: first value
* @y: second value
*/
#define umin(x, y) \
__careful_cmp(min, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
/**
* umax - return maximum of two non-negative values
* @x: first value
* @y: second value
*/
#define umax(x, y) \
__careful_cmp(max, (x) + 0u + 0ul + 0ull, (y) + 0u + 0ul + 0ull)
/**
* 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(min, (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(max, (type)(x), (type)(y))
/*
* 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 __unqual_scalar_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); \
__unqual_scalar_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 */
