[Shootout-list] Mandelbrot

[Greg Buchholz]

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--- Isaac Gouy <igouy2@yahoo.com> wrote:

> afaict the mandelbrot program spends most time writing the file?
> 

    One way to reduce time spent writing files it to use another image
file format.  Using the *.pgm format (a relative of *.ppm) with "P5" as
the magic number results in a file 1/12th the size.  

http://www.die.net/doc/linux/man/man5/pgm.5.html

(You end up writing one byte per pixel, instead of 3 ASCII chars for each
red, green, and blue component = 9 bytes + white space)

And you could really reduce the file size by converting to *.pbm (magic
number "P4") where you only use one bit per pixel.

http://www.die.net/doc/linux/man/man5/pbm.5.html

Those are all pretty simple file formats and you have the advantage of
being able to view them with a wide variety of tools.  I guess I'm
partial to having a pretty picture as output, rather than just a table of
numbers.  Attached is a C program which spits out a *.pgm file.  It's
only about 25% faster on my machine than the full *.ppm version.

Greg Buchholz




		
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//Mandelbrot benchmark
//compile:  gcc -O2 -o fractal fractal.c
//run:  fractal 600 >mandel.pgm
//by Greg Buchholz

#include<stdio.h>

int main (int argc, char **argv)
{
    int w, h, x, y;
    int i, iter = 50;
    double limit = 2.0;
    double Zr, Zi, Cr, Ci, Tr, Ti;
    
    w = atoi(argv[1]);
    h = w;

    printf("P5\n%d %d\n255\n",w,h);

    for(y=0;y<h;y++) 
    {
        for(x=0;x<w;x++)
        {
            Zr = 0.0; Zi = 0.0;
            Cr = (2*(double)x/w - 1.5); Ci=(2*(double)y/h - 1);
        
            for (i=0;i<iter;i++)
            {
                Tr = Zr*Zr - Zi*Zi + Cr;
                Ti = 2*Zr*Zi + Ci;
                Zr = Tr; Zi = Ti;
                if (Zr*Zr+Zi*Zi > limit*limit)
                    break;
            }
        
            if(Zr*Zr+Zi*Zi > limit*limit) 
                putc(255,stdout);
            else
                putc(0,stdout); 
        }
    }	

    return(0);
}

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