[LLVMdev] Impressive performance result for LLVM: complex arithmetic

[Jon Harrop]

Following a discussion about numerical performance on comp.lang.functional 
recently I just tried running a simple C mandelbrot benchmark that uses C99's 
complex arithmetic using gcc and llvm-gcc on a 2.1GHz Opteron 2352 running 
Debian:

gcc:      5.727s
llvm-gcc: 1.393s

There is still 20% room for improvement but LLVM is >4x faster than gcc here. 
Sweet.

Here's the code:

#include <stdio.h>
#include <stdlib.h>
#include <complex.h>

int max_i = 65536;

double sqr(double x) { return x*x; }

double cnorm2(complex z) { return sqr(creal(z)) + sqr(cimag(z)); }

int loop(complex c) {
    complex z=c;
    int i=1;
    while (cnorm2(z) <= 4.0 && i++ < max_i)
        z = z*z + c;
    return i;
}

int main() {
    for (int j = -39; j < 39; ++j) {
        for (int i = -39; i < 39; ++i)
            printf(loop(j/40.0-0.5 + i/40.0*I) > max_i ? "*" : " ");
        printf("\n");
    }
    return 0;
}

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e