Performance of tables slower than built in?

[Ola Fosheim Grøstad]

With linear interpolation you get roughly the same result with 
floats, a little more efficient too (half the memory and a bit 
faster):

__gshared float[512+1] QuarterSinTab;

void init(){
     const auto res = QuarterSinTab.length-1;
     for(int i = 0; i < res; i++)
         QuarterSinTab[i] = sin(PI*(0.5*i/cast(double)res));	
	QuarterSinTab[$-1] = sin(PI*0.5);
}

auto fastQuarterLookup(float x){
     const uint mantissa = cast(uint)( (x - floor(x)) * 
(cast(float)(1U<<24)) );
     const float sign = cast(float)(1 - 
cast(int)((mantissa>>22)&2));
     const uint phase = 
(mantissa^((1U<<23)-((mantissa>>22)&1)))&((1U<<23) -1);
     const uint quarterphase = (phase>>13)&511;
     const float frac = 
cast(float)(phase&((1U<<13)-1))*cast(float)(1.0f/(1U<<13));
     return sign*((1.0f-frac)*QuarterSinTab[quarterphase] + 
frac*QuarterSinTab[quarterphase+1]);
}