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Code: Select all

nt16 n = (LinearIris + 50) / 1000;
// now n equals the index + 1 of the correct T-stop without fraction (because n is an integer value)
// +50 is just because of rounding

n -= 1;
// subtract an offset of -1 to get the correct index
double FullAperture = exp2((double)n / 2);

// now calc 2^(n/2). n/2 has to be calculated float, result FullAperature is also floating point
 
To get the [1/10] of Aperture Stop out of the fraction do the following:
// get the fraction
int16 FractionAperture = (LinearIris + 50) % 1000;

// get the Aperture Tenth
int16 ApertureTenth = FractionAperture / 100;
 

Code: Select all

 
void printApertureValue(U32 apertureValue)
{
[i]    // Standard full-stop f-number scale
    // (conventional rounding of sqrt(2.0^N) N=-1,0,1,2,...,16)[/i]
    double fNumberScale[18] = {0.7,1.0,1.4,2,2.8,4,5.6,8,11,16,22,32,45,64,90,128,180,256};
 
 
    int linearIris = apertureValue + 50; // + 50 for rounding
 
    int fullApertureIdx  = linearIris / 1000;
    int fractionAperture = linearIris % 1000;
    int apertureTenth    =  fractionAperture / 100;
   
    if(0 <= fullApertureIdx && fullApertureIdx < 18)
    {
           if(apertureTenth == 0)
           {
                  printf("%.1f\n", fNumberScale[fullApertureIdx]);
           }
           else
           {
                  printf("%.1f + %d/10\n", fNumberScale[fullApertureIdx], apertureTenth);
           }
    }
    else
    {
           printf("out of bounds\n");
    }
}