mandelbrot C++ g++ #2 program

// The Computer Language Benchmarks Game
// https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
//
// contributed by Elam Kolenovic

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <iterator>
#include <limits>
#include <sstream>
#include <string>
#include <vector>

int main(int argc, char* argv[])
{
    typedef unsigned char Byte;

    const size_t N             = std::max(0, (argc > 1) ? atoi(argv[1]) : 0);
    const size_t width         = N;
    const size_t height        = N;
    const size_t maxX          = (width + 7) / 8;
    const size_t maxIterations = 50;
    const double limit         = 2.0;
    const double limitSq       = limit * limit;

    std::vector<Byte> data(height * maxX);

    for (size_t y = 0; y < height; ++y)
    {
        const double ci0  = 2.0 * y / height - 1.0;
        Byte*        line = &data[y * maxX];

        for (size_t x = 0; x < maxX; ++x)
        {
            double cr0[8];
            for (size_t k = 0; k < 8; ++k)
            {
                cr0[k] = 2.0 * (8 * x + k) / width - 1.5;
            }

            double cr[8];
            std::copy(cr0, cr0 + 8, &cr[0]);

            double ci[8];
            std::fill(ci, ci + 8, ci0);

            Byte bits = 0;
            for (size_t i = 0; i < maxIterations && bits != 0xFF; ++i)
            {
                double cr2[8];
                double ci2[8];
                double crci[8];

                for (size_t k = 0; k < 8; ++k)
                {
                    const Byte mask = (1 << (7 - k));
                    if ((bits & mask) == 0)
                    {
                        cr2[k]  = cr[k] * cr[k];
                        ci2[k]  = ci[k] * ci[k];
                        crci[k] = cr[k] * ci[k];

                        cr[k] = cr2[k] - ci2[k] + cr0[k];
                        ci[k] = 2.0 * crci[k] + ci0;

                        if (cr2[k] + ci2[k] > limitSq)
                        {
                            bits |= mask;
                        }
                    }
                }
            }
            line[x] = ~bits;
        }
    }

    std::cout << "P4\n" << width << ' ' << height << '\n';
    for (size_t y = 0; y < height; ++y)
    {
        Byte* line = reinterpret_cast<Byte*>(&data[y * maxX]);
        std::copy(line, line + width / 8, std::ostream_iterator<Byte>(std::cout));
    }

    return 0;
}
    

NOTES:
64-bit Ubuntu quad core
g++ (Ubuntu 9.3.0-10ubuntu2) 9.3.0


Mon, 04 May 2020 18:41:57 GMT

MAKE:
/usr/bin/g++ -c -pipe -O3 -fomit-frame-pointer -march=core2   mandelbrot.gpp-2.c++ -o mandelbrot.gpp-2.c++.o &&  \
        /usr/bin/g++ mandelbrot.gpp-2.c++.o -o mandelbrot.gpp-2.gpp_run  
rm mandelbrot.gpp-2.c++

5.17s to complete and log all make actions

COMMAND LINE:
./mandelbrot.gpp-2.gpp_run 16000

(BINARY) PROGRAM OUTPUT NOT SHOWN