Messages in this thread Patch in this message | | | From | David Laight <> | Subject | [PATCH 1/1] minmax.h: Slightly relax the type checking done by min() and max(). | Date | Fri, 25 Nov 2022 15:00:42 +0000 |
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Slightly relax the type checking done by min() and max(). - Promote signed/unsiged char/short to int prior to the type test. This matches what the compiler does before doing the comparison. - Skip the type test if either argument is a positive 'int' constant. Instead cast the constant to 'int', the compiler may promote it back to 'unsigned int' when doing the test.
Reduces the need to use min_t/max_t() and the possibly unwanted side effects if a type that is too small is specified.
Signed-off-by: David Laight <David.Laight@aculab.com> --- include/linux/minmax.h | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-)
diff --git a/include/linux/minmax.h b/include/linux/minmax.h index 5433c08fcc68..77de234cf502 100644 --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -9,15 +9,28 @@ * * - 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(). + * - perform 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). + * + * The type-check need not be strict in all cases: + * - char and short can be promoted to int. + * - comparisons against non-negative constant integers can be done by + * casting the constant to (int). */ +#define __is_constzero(x) \ + (sizeof(*(1 ? ((void *)((long)(x))) : (int *)0)) == sizeof(void *)) + +#define __is_positive_int(x) __is_constzero((long)(x) >> 31) +#define __maybe_int_cast(x) __builtin_choose_expr(__is_positive_int(x), (int)(long)(x), x) + +#define __typecheck_ptr_type(x, y) \ + (1 ? (void *)!(__is_positive_int(x) || __is_positive_int(y)) : (typeof((x) + 0) *)0) + #define __typecheck(x, y) \ - (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1))) + (!!(sizeof(__typecheck_ptr_type(x, y) == __typecheck_ptr_type(y, x)))) #define __no_side_effects(x, y) \ (__is_constexpr(x) && __is_constexpr(y)) @@ -25,7 +38,8 @@ #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_maybe_int(x, y, op) ((x) op (y) ? (x) : (y)) +#define __cmp(x, y, op) __cmp_maybe_int(__maybe_int_cast(x), __maybe_int_cast(y), op) #define __cmp_once(x, y, unique_x, unique_y, op) ({ \ typeof(x) unique_x = (x); \ -- 2.17.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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