pi.cpp

#include <faasm/faasm.h>
#include <faasm/input.h>
#include <faasm/random.h>

#include <stdio.h>
#include <string>
#include <vector>

#define CHUNK_SIZE 100000
#define PI 3.14159

int piStep()
{
    int count = 0;
    for (int i = 0; i < CHUNK_SIZE; i++) {
        // Two random points
        double x = faasm::randomFloat();
        double y = faasm::randomFloat();

        // Check if within unit circle
        if (x * x + y * y <= 1.0) {
            count = count + 1;
        }
    }

    // Append count for this worker
    faasmAppendState("pi", BYTES(&count), sizeof(int));
    return 0;
}

/**
 * Parallel estimation of pi
 */
int main(int argc, char* argv[])
{
    std::string inputData = faasm::getStringInput("4");
    int nWorkers = std::stoi(inputData);
    int nTotal = CHUNK_SIZE * nWorkers;

    // Dispatch chained calls
    faasmChainBatch(piStep, "", nWorkers);

    // Read in the counts
    size_t buffSize = nWorkers * sizeof(int);
    auto buffer = new int[nWorkers];
    faasmReadAppendedState("pi", (uint8_t*)buffer, buffSize, nWorkers);

    // Sum the counts
    int finalCount = 0;
    for (int w = 0; w < nWorkers; w++) {
        finalCount += buffer[w];
    }

    // Estimate pi
    float pi = 4 * ((float)finalCount / (nTotal));
    float error = abs(PI - pi);

    std::string output = "Pi estimate: " + std::to_string(pi) + "(error " +
                         std::to_string(error) + ")\n";
    printf("%s", output.c_str());
    faasm::setStringOutput(output.c_str());

    delete[] buffer;
    return 0;
}