[FFmpeg-devel] [PATCH]levc/hevc_cabac Optimise ff_hevc_hls_residual_coding (especially ARM)

[John Cox]

On Tue, 19 Jan 2016 14:09:22 -0300, you wrote:

>On 1/19/2016 2:05 PM, John Cox wrote:
>>> On 1/19/2016 9:46 AM, John Cox wrote:
>>>> +// Helper fns
>>>> +#ifndef hevc_mem_bits32
>>>> +static av_always_inline uint32_t hevc_mem_bits32(const void * buf, const unsigned int offset)
>>>> +{
>>>> +    return AV_RB32((const uint8_t *)buf + (offset >> 3)) << (offset & 7);
>>>> +}
>>>> +#endif
>>>> +
>>>> +#if AV_GCC_VERSION_AT_LEAST(3,4) && !defined(hevc_clz32)
>>>> +#define hevc_clz32 hevc_clz32_builtin
>>>> +static av_always_inline unsigned int hevc_clz32_builtin(const uint32_t x)
>>>> +{
>>>> +    // __builtin_clz says it works on ints - so adjust if int is >32 bits long
>>>> +    return __builtin_clz(x) - (sizeof(int) * 8 - 32);
>>>
>>> Why aren't you simply using ff_clz?
>> 
>> Because it doesn't exist? or at least I can't find it.
>> 
>>>> +}
>>>> +#endif
>>>> +
>>>> +// It is unlikely that we will ever need this but include for completeness
>>>
>>> There are at least two compilers we support that don't define __GNUC__, so
>>> it would be used.
>>> And in any case, isn't all this duplicating ff_clz, which is available in
>>> libavutil/inthmath.h?
>> 
>> Are you sure of that?  I can find ff_ctz but no ff_clz...
>> I would happily be wrong.
>
>I assume you're writing this patch for the ffmpeg 2.8 branch or older, which you shouldn't.
>Always use the master branch. You'll find ff_clz there.

Yes/no - the code I wrote had to work against 2.8 as that is what
Rasperry Pi are using at the moment.  This patch is meant to be against
master so I can/will happily remove that code. (And I had the wrong
version checked out when commenting previously)

By the way - can you tell me what the behaviour of ff_clz is when ints
are 64 bits long or is that never the case?  Does it count up to 63 (I
am aware that the behaviour applied against 0 may be undefined) or does
it just work on the low 32 bits?  (I assume the former)

Thanks

JC