[FFmpeg-devel] [PATCH 5/5] lavfi: make request_frame() non-recursive.

Nicolas George george at nsup.org
Tue Dec 1 17:26:23 CET 2015

Le decadi 10 frimaire, an CCXXIV, Hendrik Leppkes a écrit :
> We generally just use ints for boolean properties, any particular
> reason this uses unsigned instead?

Just a matter of personal habit, justified below. But as I look at it, I see
it is rather inconsistent with other fields in the struct that are int
although they really would be better unsigned. Will change.

When it does not matter, I usually use unsigned instead of signed because
that often leaves the compiler more room for optimization. For example,
"type half(type x) { return x / 2; }" compiles into this for unsigned:

        movl    %edi, %eax
        shrl    %eax

And this for signed:

        movl    %edi, %eax
        movl    $2, %ecx
        idivl   %ecx

In other words, "x / 2" can be optimized into "x >> 1" for unsigned, but not
for signed because the rounding is not the same for negative.

I suppose in fact you already knew that. Of course it does not make a
difference here, but I prefer this habit instead of the other way around.
For booleans, I feel that int gives the impression there is a third case,
possibly error: think of ssize_t for the return value of syscalls. And if it
becomes a counter, then it should naturally be unsigned.


  Nicolas George
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