I just wondered why DM was so much slower (about 10 times) than other
compilers (on a "silly" test program) and noticed that the culprit was a
conversion from unsigned long to double.

Let's have a look at the generated code:

double f(long l)
{
  return l;
}

generated code:
  fild    dword ptr 4[ESP]
  ret


But:

double g(unsigned long l)
{
  return l;
}

generated code:
  push    EAX
  push    EAX
  mov     EAX,0Ch[ESP]
  call    near ptr __ULNGDBL@
  mov     [ESP],EAX
  mov     4[ESP],EDX
  fld     qword ptr [ESP]
  add     ESP,8
  ret

Most other compilers seem to convert the function g to something like:

double g(unsigned long l)
{
  return (long long) l;
}

which usually is much faster (because it doesn't need to call a helper
function):
  push    EAX
  xor     ECX,ECX
  push    EAX
  mov     EAX,0Ch[ESP]
  mov     [ESP],EAX
  mov     4[ESP],ECX
  fild    long64 ptr [ESP]
  add     ESP,8
  ret

(all compiled with "-cpp -o+all -ff")


bye, Christof

-- 
http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de

...and what have you contributed to the Net?

Yes, that's better code. -Walter

"Christof Meerwald" <cmeerw@web.de> wrote in message news:b1mofb$9i7$1@digitaldaemon.com...
> I just wondered why DM was so much slower (about 10 times) than other
> compilers (on a "silly" test program) and noticed that the culprit was a
> conversion from unsigned long to double.
>
> Let's have a look at the generated code:
>
> double f(long l)
> {
>   return l;
> }
>
> generated code:
>   fild    dword ptr 4[ESP]
>   ret
>
>
> But:
>
> double g(unsigned long l)
> {
>   return l;
> }
>
> generated code:
>   push    EAX
>   push    EAX
>   mov     EAX,0Ch[ESP]
>   call    near ptr __ULNGDBL@
>   mov     [ESP],EAX
>   mov     4[ESP],EDX
>   fld     qword ptr [ESP]
>   add     ESP,8
>   ret
>
> Most other compilers seem to convert the function g to something like:
>
> double g(unsigned long l)
> {
>   return (long long) l;
> }
>
> which usually is much faster (because it doesn't need to call a helper
> function):
>   push    EAX
>   xor     ECX,ECX
>   push    EAX
>   mov     EAX,0Ch[ESP]
>   mov     [ESP],EAX
>   mov     4[ESP],ECX
>   fild    long64 ptr [ESP]
>   add     ESP,8
>   ret
>
> (all compiled with "-cpp -o+all -ff")
>
>
> bye, Christof
>
> --
> http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de
>
> ...and what have you contributed to the Net?