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char *string_repeat(const char *str, int n)
{
   char *pa, *pb;
   size_t slen = strlen(str);
   char *dest = malloc(n*slen+1);

   pa = dest + (n-1)*slen;
   strcpy(pa, str);
   pb = --pa + slen;
   while (pa>=dest) *pa-- = *pb--;
   return dest;
}