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편집 파일: 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))) /* * __sign_use for integer expressions: * bit #0 set if ok for unsigned comparisons * bit #1 set if ok for signed comparisons * * In particular, statically non-negative signed integer * expressions are ok for both. * * NOTE! Unsigned types smaller than 'int' are implicitly * converted to 'int' in expressions, and are accepted for * signed conversions for now. This is debatable. * * Note that 'x' is the original expression, and 'ux' is * the unique variable that contains the value. * * We use 'ux' for pure type checking, and 'x' for when * we need to look at the value (but without evaluating * it for side effects! Careful to only ever evaluate it * with sizeof() or __builtin_constant_p() etc). * * Pointers end up being checked by the normal C type * rules at the actual comparison, and these expressions * only need to be careful to not cause warnings for * pointer use. */ #define __signed_type_use(x,ux) (2+__is_nonneg(x,ux)) #define __unsigned_type_use(x,ux) (1+2*(sizeof(ux)<4)) #define __sign_use(x,ux) (is_signed_type(typeof(ux))? \ __signed_type_use(x,ux):__unsigned_type_use(x,ux)) /* * To avoid warnings about casting pointers to integers * of different sizes, we need that special sign type. * * On 64-bit we can just always use 'long', since any * integer or pointer type can just be cast to that. * * This does not work for 128-bit signed integers since * the cast would truncate them, but we do not use s128 * types in the kernel (we do use 'u128', but they will * be handled by the !is_signed_type() case). * * NOTE! The cast is there only to avoid any warnings * from when values that aren't signed integer types. */ #ifdef CONFIG_64BIT #define __signed_type(ux) long #else #define __signed_type(ux) typeof(__builtin_choose_expr(sizeof(ux)>4,1LL,1L)) #endif #define __is_nonneg(x,ux) statically_true((__signed_type(ux))(x)>=0) #define __types_ok(x,y,ux,uy) \ (__sign_use(x,ux) & __sign_use(y,uy)) #define __types_ok3(x,y,z,ux,uy,uz) \ (__sign_use(x,ux) & __sign_use(y,uy) & __sign_use(z,uz)) #define __cmp_op_min < #define __cmp_op_max > #define __cmp(op, x, y) ((x) __cmp_op_##op (y) ? (x) : (y)) #define __cmp_once_unique(op, type, x, y, ux, uy) \ ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); }) #define __cmp_once(op, type, x, y) \ __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_)) #define __careful_cmp_once(op, x, y, ux, uy) ({ \ __auto_type ux = (x); __auto_type uy = (y); \ BUILD_BUG_ON_MSG(!__types_ok(x,y,ux,uy), \ #op"("#x", "#y") signedness error"); \ __cmp(op, ux, uy); }) #define __careful_cmp(op, x, y) \ __careful_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, uval, ulo, uhi) ({ \ __auto_type uval = (val); \ __auto_type ulo = (lo); \ __auto_type uhi = (hi); \ static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \ (lo) <= (hi), true), \ "clamp() low limit " #lo " greater than high limit " #hi); \ BUILD_BUG_ON_MSG(!__types_ok3(val,lo,hi,uval,ulo,uhi), \ "clamp("#val", "#lo", "#hi") signedness error"); \ __clamp(uval, ulo, uhi); }) #define __careful_clamp(val, lo, hi) \ __clamp_once(val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_)) /** * 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) __cmp_once(min, type, x, 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) __cmp_once(max, type, x, 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) /* * Use these carefully: no type checking, and uses the arguments * multiple times. Use for obvious constants only. */ #define MIN(a,b) __cmp(min,a,b) #define MAX(a,b) __cmp(max,a,b) #define MIN_T(type,a,b) __cmp(min,(type)(a),(type)(b)) #define MAX_T(type,a,b) __cmp(max,(type)(a),(type)(b)) #endif /* _LINUX_MINMAX_H */