hi folks

why is the fpu rounding my result ?

Result gives me 16
should be 15,966386554621848739495798319328
i only need 15,96
Can somebody explain what i doing wrong?

Kind Regards
jpam

local MyNumber:dword
local Divider:dword
local Result:dword

mov , 1900
mov , 119
mov , 1900
mov , 119

FILD MyNumber
FILD Divider                         
FDIV 
FIST Result

DbgDec Result
DbgFloat Result
Posted on 2009-08-24 05:50:01 by jpam

Firstly, you're storing the result as a 32bit INTEGER, not a float.
So don't expect to make sense of DbgFloat output!

Secondly, you're not popping the value from ST(0), you left it there!

FIST = store result as integer, dont pop a value from the fpu stack
FISTP = store result as integer, DO pop a value from the fpu stack
FST = store as float, no pop
FSTP = store as float, with pop

Also : You can get more fpu accuracy by using REAL8 or REAL10 data types.
These are bigger yes, but easy to use.

eg
local Result:REAL8 (or REAL10) for floats

or
local Result:QWORD (or TWORD) for integers


As you noticed, you can specify dword in place of real4 (etc) without generating errors, masm wont care if the data types are the same size.


Posted on 2009-08-24 08:49:16 by Homer
should be 15,966386554621848739495798319328


This is another detail you have to learn. The BEST you can expect from the FPU (with extended-double precision) is equivalent to approximately 19 digits in the decimal system. Thus don't expect to ever get anything more precise than:
15,96638655462184874

If you intend to continue using the FPU without too much stumbling, you can have a glance at the following if you are not yet aware of it:
http://www.ray.masmcode.com/tutorial/index.html
Posted on 2009-08-24 22:03:36 by Raymond
Don't panic! The learning curve is not very steep, it wasn't so long ago that I was in your position.
Feel free to ask questions, don't be put off by the tone of my previous response, we're here to help :)
You are starting exactly the right way, with simple fpu calculations, and with the benefit of runtime debug support.
Posted on 2009-08-25 02:20:35 by Homer
Thanks Homer & Raymond

i use the REAL4 now
the Result is now 1.596638679504E+0001

allmost good, but the decimal point should be after the 5, like 15.96638679504E+0001

The fpu tutorial was allready in my masm dir and is now my main study object :)

current code

local MyNumber:REAL4
local Divider:REAL4
local Result:REAL4

mov , 1900
mov , 119

FLD MyNumber                   
FLD Divider                                           
FDIV             
FSTP Result             

DbgDec Result
DbgFloat Result


Posted on 2009-08-25 05:54:23 by jpam
Looks OK to me: 1900 / 119 = ~15.9 = ~1.59E+1 It's called scientific notation. So your code is now correct :)
Posted on 2009-08-25 06:54:07 by ti_mo_n
Yeah - the E+1 can be thought of as "shift the decimal point by +1 places", or "*10 ^1"

So 1.50 becomes 15.0

And it works similarly for negative values such as E-3 (ie /10 ^3, ie /1000)

For very big or very small numbers, it means we dont have to print a whole bunch of zeroes to express the value.
Posted on 2009-08-25 07:32:23 by Homer
If the code is correct
how do i get rid of that E notation

i only want that my result outputs 15.96

???

Posted on 2009-08-25 07:49:47 by jpam
The notation depends only on the tool you use to view the value. The binary form is 417F7652 (32-bit float which yields about 6 significant decimal digits -- see IEEE-754). It's up to you how you present it to the user. It can be 15.9663 or 1.59663E+1 or whatever.
Posted on 2009-08-25 08:01:07 by ti_mo_n
Unfortunately, DbgFloat macro doesn't let you do that.
But you can do it yourself with a few more lines :)

Inside the DbgFloat macro is a call to a procedure called ST0ToStr.


; Arguments: Arg1: Pointer to destination buffer (at least 20 bytes + padding bytes).
;            Arg2: Number of padding bytes.
;            Arg3: Number of decimal places.
;            Arg4: Format flag (f_NOR or f_SCI)


local stringbuffer[256]:BYTE

local MyNumber:REAL4
local Divider:REAL4
local Result:REAL4

mov , 1900
mov , 119

FLD MyNumber                    
FLD Divider                                            
FDIV              
FST Result      ;leaving it on the FPU in ST(0) as an input param to the following call
lea eax,stringbuffer    ;we have to supply Pointer to buffer that receives output string
invoke St0ToStr, eax, 0, 15, f_NOR   ;no padding, 15 places, normal notation
fUnload       ;super secret OA32 macro for popping ST(0) from the fpu stack
DbgStr stringbuffer   ;Display the string




I doubt that Biterider will bother adding a Flags argument to the DbgFloat macro, but you never know ;)
BTW - DbgFloat already has 4 possible arguments, you should read the comments for DbgFloat (in Debug.inc)

Posted on 2009-08-25 10:36:46 by Homer
wow !

youre my hero Homer :)

only had to add % include &MacPath&fMath.inc for the f_NOR constant
and the fUnload command

next time i have to search deeper in those inc and lib files :)

many thanks Homer to show me how to use those commands !

Kind regards
jpam
Posted on 2009-08-25 10:59:26 by jpam
You can eliminate one instruction

FLD MyNumber      ST(0) = MyNumber                                                           
FDIV Divider          ST(0) = ST(0) / Divider , which is our result
FST Result            ST(0)  still contains the result
Posted on 2009-08-25 11:14:16 by Homer
jpam,

If the tutorial was already in your MASM32 folder, you should also have the Fpulib. It has a conversion function (FpuFLtoA) where you can specify the number of digits after the decimal delimiter, whether you want the result in regular or scientific notation, and how many leading blanks you need for alignment of the decimal delimiter. The only drawback is that, if the float is in memory, it needs to be in the REAL10 format (if it is in the top FPU register, it's already in REAL10 format).
Posted on 2009-08-25 15:34:57 by Raymond
Thanks Raymond

i allready notice that function FpuFLtoA
and i saw alot other very nice functions  :P

But Homer's solution is working perfect for me

i am trying alot different functions and fpu commands in my test app
just for learning purpose

Thanks for all the help guys
Posted on 2009-08-25 17:30:15 by jpam