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Message-ID: <760fed5020ac42419cb0c3579ba1ed6c@AcuMS.aculab.com> Date: Sun, 28 Jan 2024 19:27:51 +0000 From: David Laight <David.Laight@...LAB.COM> To: "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>, "'Linus Torvalds'" <torvalds@...ux-foundation.org>, 'Netdev' <netdev@...r.kernel.org>, "'dri-devel@...ts.freedesktop.org'" <dri-devel@...ts.freedesktop.org> CC: 'Andy Shevchenko' <andriy.shevchenko@...ux.intel.com>, 'Andrew Morton' <akpm@...ux-foundation.org>, "'Matthew Wilcox (Oracle)'" <willy@...radead.org>, 'Christoph Hellwig' <hch@...radead.org>, "'Dan Carpenter'" <dan.carpenter@...aro.org>, 'Linus Walleij' <linus.walleij@...aro.org>, "'David S . Miller'" <davem@...emloft.net>, "'linux-btrfs@...r.kernel.org'" <linux-btrfs@...r.kernel.org>, 'Jens Axboe' <axboe@...nel.dk> Subject: RE: [PATCH next 03/11] minmax: Simplify signedness check It is enough to check that both 'x' and 'y' are valid for either a signed compare or an unsigned compare. For unsigned they must be an unsigned type or a positive constant. For signed they must be signed after unsigned char/short are promoted. The predicate for _Static_assert() only needs to be a compile-time constant not a constant integeger expression. In particular the short-circuit evaluation of || && ?: can be used to avoid the non-constantness of (pointer_type)1 in is_signed_type(). The '+ 0' in '(x) + 0 > = 0' is there to convert 'bool' to 'int' and avoid a compiler warning because max() gets used for 'bool' in one place (a very expensive 'or'). (The code is optimised away by two earlier checks - but the compiler still bleats.) Signed-off-by: David Laight <david.laight@...lab.com> --- include/linux/minmax.h | 22 ++++++++++------------ 1 file changed, 10 insertions(+), 12 deletions(-) diff --git a/include/linux/minmax.h b/include/linux/minmax.h index 900eec7a28e5..c32b4b40ce01 100644 --- a/include/linux/minmax.h +++ b/include/linux/minmax.h @@ -8,7 +8,7 @@ #include <linux/types.h> /* - * min()/max()/clamp() macros must accomplish three things: + * min()/max()/clamp() macros must accomplish several things: * * - Avoid multiple evaluations of the arguments (so side-effects like * "x++" happen only once) when non-constant. @@ -26,19 +26,17 @@ #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) +/* Allow unsigned compares against non-negative signed constants. */ +#define __is_ok_unsigned(x) \ + (is_unsigned_type(typeof(x)) || (__is_constexpr(x) ? (x) + 0 >= 0 : 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) +/* Check for signed after promoting unsigned char/short to int */ +#define __is_ok_signed(x) is_signed_type(typeof((x) + 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)) +/* Allow if both x and y are valid for either signed or unsigned compares. */ +#define __types_ok(x, y) \ + ((__is_ok_signed(x) && __is_ok_signed(y)) || \ + (__is_ok_unsigned(x) && __is_ok_unsigned(y))) #define __cmp_op_min < #define __cmp_op_max > -- 2.17.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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