Hi Andy,
On Wed, 14 Jun 2023 14:51:43 +0300 Andy Shevchenko andy.shevchenko@gmail.com wrote:
On Wed, Jun 14, 2023 at 12:42 PM Herve Codina herve.codina@bootlin.com wrote:
On Wed, 14 Jun 2023 12:02:57 +0300 Andy Shevchenko andy.shevchenko@gmail.com wrote:
On Wed, Jun 14, 2023 at 10:49 AM Herve Codina herve.codina@bootlin.com wrote:
...
typeof(__array[0] + 0) __element = __array[--__len]; \Do we need the ' + 0' part?
Yes.
__array can be an array of const items and it is legitimate to get the minimum value from const items.
typeof(__array[0]) keeps the const qualifier but we need to assign __element in the loop. One way to drop the const qualifier is to get the type from a rvalue computed from __array[0]. This rvalue has to have the exact same type with only the const dropped. '__array[0] + 0' was a perfect canditate.
Seems like this also deserves a comment. But if the series is accepted as is, it may be done as a follow up.
Finally not so simple ... I did some deeper tests and the macros need to be fixed.
I hope this one (with comments added) is correct: --- 8 --- /* * 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< --- * * The first typeof(&(array)[0]) is needed in order to support arrays of both * 'int *buff' and 'int buf[N]' types. * * typeof(__array[0] + 0) used for __element is needed as the array can be an * array of const items. * In order to discard the const qualifier use an arithmetic operation (rvalue). * This arithmetic operation discard the const but also can lead to an integer * promotion. For instance, a const s8 __array[0] lead to an int __element due * to the promotion. * In this case, simple min() or max() operation fails (type mismatch). * Use min_t() or max_t() (op_t parameter) enforcing the type in order to avoid * the min() or max() failure. */ #define __minmax_array(op_t, array, len) ({ \ typeof(&(array)[0]) __array = (array); \ typeof(len) __len = (len); \ typeof(__array[0] + 0) __element = __array[--__len]; \ while (__len--) \ __element = op_t(typeof(__array[0]), __element, __array[__len]); \ __element; })
/** * min_array - return minimum of values present in an array * @array: array * @len: array length * * Note that @len must not be zero (empty array). */ #define min_array(array, len) __minmax_array(min_t, array, len)
/** * max_array - return maximum of values present in an array * @array: array * @len: array length * * Note that @len must not be zero (empty array). */ #define max_array(array, len) __minmax_array(max_t, array, len)
--- 8< ---
Tested ok from user-space on my x86_64 using the following types for *buff and buff[N]: - signed/unsigned char - signed/unsigned short - signed/unsigned int - signed/unsigned long - signed/unsigned long long - float, double, long double (even if not used in the kernel)
Can you give me your feedback on this last version ?
If you are ok, it will be present in the next iteration of the series. Otherwise, as a last ressort, I will drop the {min,max}_array() and switch back to the specific min/max computation in IIO inkern.c
Sorry for this back and forth and this last minute detected bug.
Best regards, Hervé