[FFmpeg-devel] [PATCH] intmath: remove av_ctz.

[Ganesh Ajjanagadde]

On Sun, Oct 11, 2015 at 9:12 PM, Ganesh Ajjanagadde <gajjanag at mit.edu> wrote:
> On Sun, Oct 11, 2015 at 6:04 PM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>> Hi,
>>
>> On Sun, Oct 11, 2015 at 5:52 PM, Andreas Cadhalpun <
>> andreas.cadhalpun at googlemail.com> wrote:
>>
>>> On 11.10.2015 23:44, Ronald S. Bultje wrote:
>>> > It's a non-installed header and only used in one place (flacenc).
>>> > Since ff_ctz is static inline, it's fine to use that instead.
>>> > ---
>>> >  doc/APIchanges       |  3 ---
>>> >  libavcodec/flacenc.c |  2 +-
>>> >  libavutil/intmath.c  |  5 -----
>>> >  libavutil/intmath.h  | 14 ++++++--------
>>> >  4 files changed, 7 insertions(+), 17 deletions(-)
>>>
>>> Should be fine.
>>
>>
>> Thanks, pushed.
>
> Since there is still time, and I did not think of this before, I would
> like to replace ff_ctz with ff_ctz32. There are a couple of reasons:
> 1. It is used with an int32 argument in flacenc.
> 2. I can do a deBruijn optimization for this as well. With an int also
> I could do it, but it would need some ifdefry depending on whether int
> is 32 bit or 64 bits.
>
> Let me see if I understand API/ABI with respect to this proposed
> change correctly now:
> API is not broken, as this is not public.
> ABI is broken, since the width of operands to ff_ctz has could change
> from 64 to 32 bits.

That actually raises the question of whether int = 32 bits is assumed
everywhere. For instance, if int = 64 bits, at least on the Intel
compiler, ff_ctz is broken: AFAIK, _bit_scan_forward operates on 32
bit operands.

>
>>
>> Ronald
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