Thread: I can't figure out why this C code is running so slow...

Hi,

I recently learned a fair amount of inline assembly and decided to do a little test. I wrote a selection sort in C that sorts 100,000 integers. I then wrote a inline assembly version of the same thing. I figured that the assembly version was going to be a little slower (I was pretty sloppy and didn't worry about optimization too much), but when I ran the tests I was shocked to find out that the assembly version was running twice as fast!

The C code is

Code:

   for (i = 0; i < n-1; ++i) {
      min = i;
      
      for (j = i+1; j < n; ++j)
         if (data[j] < data[min])
            min = j;
      
      if (i != min) {
         j = data[i];
         data[i] = data[min];
         data[min] = j;
      }
   }

I wrote the assembly code by looking at the C code and working my way through it. It's not heavily optimized, but it's not written extremely poorly either. My compiler is gcc 4.2.1, and I'm compiling both the C and inline assembly versions with -Wall -arch i386 -O2.

time ./test_asm < randfile.txt > outfile.txt
real 0m6.431s
user 0m6.381s
sys 0m0.012s

time ./test_c < randfile.txt > outfile.txt
real 0m13.518s
user 0m13.477s
sys 0m0.016s

Is assembly really THAT much faster??

EDIT: I am not attempting to start a flame war...