Which command line arguments are you using? Can you make use of sse2? Brian On 3/3/06, Greg Buchholz <greg@xxxxxxxxxxxxxxxxxxxx> wrote: > /* > While writing a C++ version of the Mandelbrot benchmark over at the > "The Great Computer Language Shootout"... > > http://shootout.alioth.debian.org/gp4/benchmark.php?test=mandelbrot&lang=all > > ...I've come across the issue that complex<double>'s seem painfully slow > unless compiled with -ffast-math. Of course doing that results in > incorrect answers because of rounding issues. The speed difference for > the program below is between 5x-8x depending on the version of g++. It > is also about 5 times slower than the corresponding gcc version at... > > http://shootout.alioth.debian.org/gp4/benchmark.php?test=mandelbrot&lang=gcc&id=2 > > ...I'd be interesting in learning the reason for the speed difference. > Does it have something to do with temporaries not being optimized away, > or somesuch? A limitation of the x87 instruction set? Is it inherent > in the way the C++ Standard requires complex<double>'s to be calculated? > My bad coding style? > > Curious, > > Greg Buchholz > */ > > // Takes an integer argument "n" on the command line and generates a > // PBM bitmap of the Mandelbrot set on stdout. > // see also: ( http://sleepingsquirrel.org/cpp/mandelbrot.cpp.html ) > > #include<iostream> > #include<complex> > > int main (int argc, char **argv) > { > char bit_num = 0, byte_acc = 0; > const int iter = 50; > const double limit_sqr = 2.0 * 2.0; > > std::ios_base::sync_with_stdio(false); > int n = atoi(argv[1]); > > std::cout << "P4\n" << n << " " << n << std::endl; > > for(int y=0; y<n; ++y) > for(int x=0; x<n; ++x) > { > std::complex<double> Z(0.0,0.0); > std::complex<double> C(2*(double)x/n - 1.5, 2*(double)y/n - 1.0); > > for (int i=0; i<iter and norm(Z) <= limit_sqr; ++i) Z = Z*Z + C; > > byte_acc = (byte_acc << 1) | ((norm(Z) > limit_sqr) ? 0x00:0x01); > > if(++bit_num == 8){ std::cout << byte_acc; bit_num = byte_acc = 0; } > else if(x == n-1) { byte_acc <<= (8-n%8); > std::cout << byte_acc; > bit_num = byte_acc = 0; } > } > } >
