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

[Reimar Döffinger]

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;
if (exp >= 15)
    return 0xffff;
v <<= 6;
return (v+(1<<16)) >> (15-exp);