From: Herve Codina
> Sent: 15 June 2023 16:26
>
> Introduce min_array() (resp max_array()) in order to get the
> minimal (resp maximum) of values present in an array.
>
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> ---
> include/linux/minmax.h | 64 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 64 insertions(+)
>
> diff --git a/include/linux/minmax.h b/include/linux/minmax.h
> index 396df1121bff..1672985b02a3 100644
> --- a/include/linux/minmax.h
> +++ b/include/linux/minmax.h
> @@ -133,6 +133,70 @@
> */
> #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)))
Those are probably more generally useful and belong elsewhere.
> +
> +/*
> + * 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< ---
Is that needed in the .h file?
> + *
> + * The first typeof(&(array)[0]) is needed in order to support arrays of both
> + * 'int *buff' and 'int buf[N]' types.
> + *
> + * The array can be an array of const items.
> + * typeof() keeps the const qualifier. Use __unconst_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]; \
s/__element/__bound/
> + while (__len--) \
> + __element = op(__element, __array[__len]); \
> + __element; })
I'm not all sure that all the shenanigans required to use min()
is really needed here.
It would also be generally better to process the array forwards.
So something like:
typeof (&array[0]) __ptr = array, __limit = array + len;
typeof (array[0] + 0) __element, __bound = *__ptr++;
while (ptr < __limit) {
__element = *__ptr++;
if (__element > __bound)
__bound = __element;
}
(typeof (array[0]))__bound; })
seems fine to me.
The final cast is there to convert 'int' back to un/signed char|short.
Not really needed and might generate worse code.
But if you insist on using min/max ignore this bit.
David
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