[FFmpeg-devel] [PATCH] Fast half-float to float conversion

[Jimmy Christensen]

On 2009-07-01 13:52, Reimar D?ffinger wrote:
> On Wed, Jul 01, 2009 at 01:15:35PM +0200, Reimar D?ffinger wrote:
>> On Wed, Jul 01, 2009 at 12:52:08PM +0200, Jimmy Christensen wrote:
>>> I modified for the purpose I need it for. Converting from half-float to
>>> unsigned int.
>>>
>>> uint16_t av_halflt2uint(uint16_t v){
>>>        uint16_t nosign = v+v;
>>>        if (v>>15)
>>>            return 0; // negatives are not interesting so clamp it to 0
>>>        if (nosign>= 0xfc00)
>>>            return 65535; // Anything above 1 should be clamped to 65535
>>>        if (nosign<  0x0200)
>>>            return ldexp((v&0x3ff), 1-25)*65535; // denormal or 0
>>>        return ldexp((v&0x3ff) + (1<<10), (v>>10&0x1f)-25)*65535;
>>> }
>>
>> Btw. a probably much faster but +-1 inaccurate version is:
>> int exp = v>>  10;
>> if ((v&  0x8000) || !exp)
>>      return 0;
>
> More accurate would be:
> if (v&  0x8000) return 0;
> if (!exp) return (v>>9)&1;
>
> Rounding could also be added, but that might just be overkill.

I think that would be overkill since currently there is only one (pnm) 
16-bit output format AFAIK, so for most work it gets converted down to 
8-bit anyway.

Again, thanks.

-- 
Best Regards
Jimmy Christensen
Developer
Ghost A/S