fld number1
fmul number2
frndint
fstp number3

Yup, just set the bit 10 and bit 11 of the control word to zero, then FPU will round number to the nearest, or equidistance.

.data
cword dw 0

.code
   fstcw cword           ; Get FPU control word
   fwait
   mov   ax, cword       ; Store it to AX
   and   ax, 0fffff9ffh  ; Clear bit 10 and bit 11
   push  eax
   fldcw [sp]            ; Store modified control word

   ' do your rounding here.. 


Regards,

-chris
  

            fstcw cword
            fwait
            mov ax, cword
            and   ax, 0fffff9ffh
            or ax, 0C00h
            push  eax
            fldcw [sp]            ; this line alwasy error

            fld float_buffer
            frndint
            fstp float_buffer

            ;restore some stuff
            fldcw cword
            pop eax

Sorry, that was my mistake. I'm using MASM version 8.0 which can handle 16-bit/32-bit register correction, while MASM version 6.14 (comes from MASM32v9) can't. In general, FLDCW instruction is expecting a DWORD pointer to a 16-bit data, so a more correct one is using ESP instead:

      fldcw [esp] ; ESP = 32-bit pointer to the stack

or try to reuse cword variable:

      fstcw cword 
      fwait
      mov   ax, cword
      and   ax, 0fffff9ffh
      or    ax, 0C00h
      mov   cword, ax       ; cword = changed control word
      fldcw [cword]         ; Update control word

Regards,

-chris

modchip:

I'm having a little problem again... Using the code we currently have, the result is always floored. Hmmmm... Is this what it should really do?

Input: 5.96
Output: 5

Input: 5.2
Output: 5

Anyways, I'll try to read more on Ramond's site. Later!

Regards,
m0ds

00 - Means, it round floating point to nearest whole number. I'm not sure on how to make it equidistant, because I can't make it work that way, like 5.5 should remain 5.5 etc.
01 - The rounded number is floor value., 5.9=5
10 - The rounded number is ceiling value., 5.2=6
11 - Truncates based on precision

Well, this takes a lot of trial and error, I haven't done much about it, because I prefer using Streaming SIMD Extension (SSE/SSE2 or SSE3) instructions over FPU. In FPU, you have to play with IC (Infinity Control) and PC (Precision Control), together with RC (Rounding Control) to be able to make rounding work. The initial settings of these controls are mostly for basic arithmetic.

If you have much time, I suggest start learning Streaming SIMD Extension, since Windows Vista is now blocking any call to FPU: http://www.intel.com/support/processors/sb/cs-001650.htm

You can search the Intel website for more documents about SSE, or if you're an AMD user, try working with 3DNow, documents available in their respective sites.

I also recomend this sites:
http://www.cpuid.com/ (For MMX/3DNow/SSE/SSE2/SSE3 instruction sets)
http://www.sandpile.org/ (For general CPU layout and design)

Cheers,

-chris

Whew, after 1 year, 2 months and 13 days, I finally got the solution for this. BTW, the solution is in my blog. Check it out here: http://devpinoy.org/blogs/modchip/archive/2007/08/13/round-n-round-we-go.aspx

Thanks!