Re: [FFmpeg-devel] [PATCH] swscale/input: add rgbaf16 input support

[Timo Rothenpieler <timo@rothenpieler.org>]

On 08.08.2022 21:39, Mark Reid wrote:
> On Mon, Aug 8, 2022 at 11:24 AM Timo Rothenpieler <timo@rothenpieler.org>
> wrote:
> 
>> This is by no means perfect, since at least ddagrab will return scRGB
>> data with values outside of 0.0f to 1.0f for HDR values.
>> Its primary purpose is to be able to work with the format at all.
>>
>> _Float16 support was available on arm/aarch64 for a while, and with gcc
>> 12 was enabled on x86 as long as SSE2 is supported.
>>
>> If the target arch supports f16c, gcc emits fairly efficient assembly,
>> taking advantage of it. This is the case on x86-64-v3 or higher.
>> Without f16c, it emulates it in software using sse2 instructions.
>> ---
>>
>> I am by no means certain this is the correct way to implement this.
>> Tested it with ddagrab output in that format, and it looks like what I'd
>> expect.
>>
>> Specially the order of arguments is a bit of a mystery. I'd have
>> expected them to be in order of the planes, so for packed formats, only
>> the first one would matter.
>> But a bunch of other packed formats left the first src unused, and so I
>> followed along, and it ended up working fine.
>>
>>
> Have you looked at the exr decoder half2float.h? It already has f16 to f32
> decoding functions.
> 

For performance, using the compilers native, and potentially hardware 
accelerated, support is probably preferable.
Though as a no-float16-fallback it's probably not too horrible.
Just not sure if it's worth the extra effort, given that by the time 
this sees any use at all, gcc 12 will be very common.

Might even think about _Float16 support for exr in that case.
Would be an interesting benchmark.
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