Sample a 50Hz sine and get the amplitude

sin_match.d

// Code fixed and idea taken from https://www.mikrocontroller.net/topic/211730#2100553
import std;

// Simulate a sinus in mV, with 1200 mV offset, 50 Hz frequency, sampled at 1 kHz
uint32_t measureMV()
{
    static int pos = 0;
    return cast(uint32_t)(1200 + 200 * sin(2 * PI * (pos++) * 50.0 / 1000.0));
}

// 18 Bit
int32_t tabAmp = (1 << 18);
int32_t[20] sinTab, cosTab;

// Up to 12 + log2(1000) = 22 bit
int32_t sinSum, cosSum;

size_t phaseIdx = 0;
size_t frameIdx = 0;

void onTimer()
{
    // < 12 bit
    int32_t sample = cast(int32_t) measureMV();

    // 12bit * 18 bit => 30 bit / 18 bit => 12 bit
    int32_t sinPart = (sample * sinTab[phaseIdx]) / tabAmp;
    int32_t cosPart = (sample * cosTab[phaseIdx]) / tabAmp;
    sinSum += sinPart;
    cosSum += cosPart;

    // Count up the table phase
    phaseIdx++;
    if (phaseIdx == 20)
        phaseIdx = 0;

    // Result every 1s
    frameIdx++;
    if (frameIdx == 1000)
    {
        onResult(sinSum, cosSum);

        // Reset average value
        sinSum = 0;
        cosSum = 0;
        frameIdx = 0;
    }
}

void onResult(int32_t sinSum, int32_t cosSum)
{
    double cosSumD = cast(double) cosSum;
    double sinSumD = cast(double) sinSum;

    double result = 2 * sqrt(sinSumD * sinSumD + cosSumD * cosSumD) / 1000.0;
    writeln(result);
}

void main()
{

    for (size_t i = 0; i < 20; i++)
    {
        sinTab[i] = cast(int32_t)(tabAmp * sin(2 * PI * i / 20.0));
        cosTab[i] = cast(int32_t)(tabAmp * cos(2 * PI * i / 20.0));
    }

    writeln(sinTab);
    writeln(cosTab);

    for (size_t i = 0; i < 1000; i++)
        onTimer();
}