Extended inline assembly error with gcc: impossible constraints

The other day I was reading a document about inline assembly (http://www.delorie.com/djgpp/doc/bre...ine_djgpp.html).

I got stuck at the rep_movsl code. I tried ruing it on my PC. At first I got no error when it was the only thing in the code. But when I tried to actually use it, the compiler complained "‘asm’ operand has impossible constraints".

I am unable to figure out my way. I have already googled about it, but all vain.

I was wondering if there was something wrong with my compiling command. All I am using is "gcc code.c".

I would be great if anyone could look at my code (below) and help me out.

Thnx.

#include <stdio.h>

#define rep_movsl(src, dest, numwords) 
__asm__ __volatile__ ( 
  "cldnt" 
  "repnt" 
  "movsl" 
  : : "S" (src), "D" (dest), "c" (numwords) 
  : "%ecx", "%esi", "%edi" )

int main(int argc, char const *argv[])
{
    int arr1[4] = {1, 2, 3, 4};
    int arr2[4];
    
    rep_movsl(arr1, arr2, 4);
    
    int i;
    for(i=0;i<4;++i)
        printf("%d ",arr2[i]);
    retu 0;
}