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f747e6667e
GENMASK() has an input check which uses __builtin_choose_expr() to enable a compile time sanity check of its inputs if they are known at compile time. However, it turns out that __builtin_constant_p() does not always return a compile time constant [0]. It was thought this problem was fixed with gcc 4.9 [1], but apparently this is not the case [2]. Switch to use __is_constexpr() instead which always returns a compile time constant, regardless of its inputs. Link: https://lore.kernel.org/lkml/42b4342b-aefc-a16a-0d43-9f9c0d63ba7a@rasmusvillemoes.dk [0] Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449 [1] Link: https://lore.kernel.org/lkml/1ac7bbc2-45d9-26ed-0b33-bf382b8d858b@I-love.SAKURA.ne.jp [2] Link: https://lkml.kernel.org/r/20210511203716.117010-1-rikard.falkeborn@gmail.com Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com> Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Acked-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com> Cc: Ard Biesheuvel <ardb@kernel.org> Cc: Yury Norov <yury.norov@gmail.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
147 lines
4 KiB
C
147 lines
4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_MINMAX_H
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#define _LINUX_MINMAX_H
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#include <linux/const.h>
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/*
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* min()/max()/clamp() macros must accomplish three things:
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*
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* - avoid multiple evaluations of the arguments (so side-effects like
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* "x++" happen only once) when non-constant.
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* - perform strict type-checking (to generate warnings instead of
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* nasty runtime surprises). See the "unnecessary" pointer comparison
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* in __typecheck().
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* - retain result as a constant expressions when called with only
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* constant expressions (to avoid tripping VLA warnings in stack
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* allocation usage).
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*/
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#define __typecheck(x, y) \
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(!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
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#define __no_side_effects(x, y) \
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(__is_constexpr(x) && __is_constexpr(y))
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#define __safe_cmp(x, y) \
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(__typecheck(x, y) && __no_side_effects(x, y))
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#define __cmp(x, y, op) ((x) op (y) ? (x) : (y))
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#define __cmp_once(x, y, unique_x, unique_y, op) ({ \
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typeof(x) unique_x = (x); \
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typeof(y) unique_y = (y); \
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__cmp(unique_x, unique_y, op); })
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#define __careful_cmp(x, y, op) \
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__builtin_choose_expr(__safe_cmp(x, y), \
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__cmp(x, y, op), \
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__cmp_once(x, y, __UNIQUE_ID(__x), __UNIQUE_ID(__y), op))
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/**
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* min - return minimum of two values of the same or compatible types
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* @x: first value
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* @y: second value
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*/
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#define min(x, y) __careful_cmp(x, y, <)
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/**
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* max - return maximum of two values of the same or compatible types
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* @x: first value
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* @y: second value
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*/
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#define max(x, y) __careful_cmp(x, y, >)
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/**
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* min3 - return minimum of three values
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* @x: first value
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* @y: second value
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* @z: third value
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*/
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#define min3(x, y, z) min((typeof(x))min(x, y), z)
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/**
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* max3 - return maximum of three values
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* @x: first value
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* @y: second value
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* @z: third value
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*/
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#define max3(x, y, z) max((typeof(x))max(x, y), z)
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/**
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* min_not_zero - return the minimum that is _not_ zero, unless both are zero
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* @x: value1
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* @y: value2
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*/
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#define min_not_zero(x, y) ({ \
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typeof(x) __x = (x); \
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typeof(y) __y = (y); \
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__x == 0 ? __y : ((__y == 0) ? __x : min(__x, __y)); })
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/**
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* clamp - return a value clamped to a given range with strict typechecking
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* @val: current value
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* @lo: lowest allowable value
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* @hi: highest allowable value
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*
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* This macro does strict typechecking of @lo/@hi to make sure they are of the
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* same type as @val. See the unnecessary pointer comparisons.
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*/
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#define clamp(val, lo, hi) min((typeof(val))max(val, lo), hi)
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/*
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* ..and if you can't take the strict
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* types, you can specify one yourself.
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*
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* Or not use min/max/clamp at all, of course.
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*/
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/**
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* min_t - return minimum of two values, using the specified type
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* @type: data type to use
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* @x: first value
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* @y: second value
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*/
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#define min_t(type, x, y) __careful_cmp((type)(x), (type)(y), <)
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/**
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* max_t - return maximum of two values, using the specified type
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* @type: data type to use
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* @x: first value
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* @y: second value
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*/
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#define max_t(type, x, y) __careful_cmp((type)(x), (type)(y), >)
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/**
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* clamp_t - return a value clamped to a given range using a given type
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* @type: the type of variable to use
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* @val: current value
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* @lo: minimum allowable value
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* @hi: maximum allowable value
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*
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* This macro does no typechecking and uses temporary variables of type
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* @type to make all the comparisons.
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*/
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#define clamp_t(type, val, lo, hi) min_t(type, max_t(type, val, lo), hi)
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/**
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* clamp_val - return a value clamped to a given range using val's type
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* @val: current value
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* @lo: minimum allowable value
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* @hi: maximum allowable value
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*
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* This macro does no typechecking and uses temporary variables of whatever
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* type the input argument @val is. This is useful when @val is an unsigned
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* type and @lo and @hi are literals that will otherwise be assigned a signed
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* integer type.
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*/
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#define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
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/**
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* swap - swap values of @a and @b
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* @a: first value
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* @b: second value
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*/
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#define swap(a, b) \
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do { typeof(a) __tmp = (a); (a) = (b); (b) = __tmp; } while (0)
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#endif /* _LINUX_MINMAX_H */
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