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Compute the EV more efficiently #7

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Compute the EV more efficiently #7

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257aa3b
Compute the EV more efficiently
edgar-bonet Aug 14, 2018
eb17988
Merge branch 'master' into cheap-log
edgar-bonet May 8, 2019
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18 changes: 15 additions & 3 deletions LEX/LEX.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -380,6 +380,18 @@ void debugDisplay(){
display.clearDisplay();
}

/**
Base-2 logarithm, rounded to the nearest integer
*/
int roundedLog2(float x)
{
int ex;
// The exponent returned by frexp() is the base-2 logarithm rounded up.
// Scaling by 1/sqrt(2) ensures round-to-nearest.
frexp(x * M_SQRT1_2, &ex);
return ex;
}

void updateDisplay(float T)
{
if (mode == DEBUG) {
Expand All @@ -388,7 +400,7 @@ void updateDisplay(float T)

int timeDisplayMode; // State of shutter speed value display (fractional, seconds, minutes)
int tFractionalDivisor; // Fractional time e.g. 1/1000, where tFractionalDivisor = 1000
float Ev; // Calculated Exposure Value
int Ev; // Calculated Exposure Value
float Tmin; // Time in minutes

if (T >= 60) {
Expand Down Expand Up @@ -478,8 +490,8 @@ void updateDisplay(float T)
display.println(FILM_SENSITIVITY_TABLE[sensitivityIndex], 0);
display.setCursor(76, 11);
display.print("EV=");
Ev = log(pow(APERTURE_TABLE[apertureIndex], 2)) / log(2) + log(1 / T) / log(2);
display.println(floor(Ev + 0.5), 1);
Ev = roundedLog2(pow(APERTURE_TABLE[apertureIndex], 2) / T);
display.println(Ev);
display.setCursor(76, 22);
display.print(lux, 1);
display.println("Lx");
Expand Down