Re: [PATCH] drivers:iio:dac make expression evaluation 64-bit

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On 12/23/21 5:34 PM, Muhammad Usama Anjum wrote:
On 12/22/21 11:49 PM, Andy Shevchenko wrote:
On Wed, Dec 22, 2021 at 5:59 PM Muhammad Usama Anjum
<usama.anjum@xxxxxxxxxxxxx> wrote:
Two 32-bit values are being evaluated using 32-bit arithmetic and then
passed to s64 type. It is wrong. Expression should be evaluated using
64-bit arithmetic and then passed.
...

         dac->ch_data[ch].scale_dec = DIV_ROUND_CLOSEST((s64)rem * 1000000,
                                                         65536);
Shouldn't the above be fixed as well? Has anybody tried to compile on
32-bit arch this?
No, it correct already. In this case, rem is being typecasted to s64 and
then multiplied with a 32-bit number, 1000000. Thus 64-bit arithmetic is
being performed here.

What Andy means is that this needs to be DIV_S64_ROUND_CLOSEST() to work on 32-bit platforms. But it is clearly unrelated to your change and should be in its own patch.




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