diff options
Diffstat (limited to 'include/linux/minmax.h')
| -rw-r--r-- | include/linux/minmax.h | 129 |
1 files changed, 71 insertions, 58 deletions
diff --git a/include/linux/minmax.h b/include/linux/minmax.h index 83aebc244cba..2ec559284a9f 100644 --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -2,60 +2,77 @@ #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 + * - 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 + * - 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))) -#define __no_side_effects(x, y) \ - (__is_constexpr(x) && __is_constexpr(y)) +/* 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) -#define __safe_cmp(x, y) \ - (__typecheck(x, y) && __no_side_effects(x, y)) +/* 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 __cmp(x, y, op) ((x) op (y) ? (x) : (y)) +#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_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 __cmp_op_min < +#define __cmp_op_max > -#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 __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); \ - __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 __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) ({ \ - __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), \ + __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))); }) @@ -65,14 +82,31 @@ * @x: first value * @y: second value */ -#define min(x, y) __careful_cmp(x, y, <) +#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(x, y, >) +#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 @@ -124,7 +158,7 @@ * @x: first value * @y: second value */ -#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <) +#define min_t(type, x, y) __careful_cmp(min, (type)(x), (type)(y)) /** * max_t - return maximum of two values, using the specified type @@ -132,28 +166,7 @@ * @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))) +#define max_t(type, x, y) __careful_cmp(max, (type)(x), (type)(y)) /* * Do not check the array parameter using __must_be_array(). @@ -169,13 +182,13 @@ * '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 + * 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); \ - __unconst_integer_typeof(__array[0]) __element = __array[--__len]; \ + __unqual_scalar_typeof(__array[0]) __element = __array[--__len];\ while (__len--) \ __element = op(__element, __array[__len]); \ __element; }) |