fcomip or converter problem

[RuiLoureiro]

                I type the string '0.1'
                and i convert it to _Delta
                I show both _Delta0 and _Delta and they are 0.10000000

                When i Test, it jumps to label _erro, so
                _Delta > _Delta0 !

                If _Delta <= _Delta0 it should exit with CLC
                is what i want.
               
                What is the problem ? What's the solution ?

Code Select Expand


.DATA
_Delta      dt 0
_Delta0     dt 1.0e-1   
;.............................

                ; -----------
                ; Test _Delta
                ; -----------
                fld     tbyte ptr _Delta0       ;st(1)
                fld     tbyte ptr _Delta        ;st(0)
                ;
                fcomip  st(0), st(1)
                fwait
                jpe     short _erro1
                ja      short _erro

                fstp    st                      ;remove source
                clc
                ret

    _erro1:     fstp    st                      ;remove source
                mov     eax, 1
                stc
                ret     
                ;
                ; EXIT  «««HERE !!!
                ;
    _erro:      fstp    st                      ;remove source
                mov     eax, 0
                stc
                ret


    I decided to use my converter and do this
    and now _Delta = _Delta0
   

Code Select Expand


.DATA
_sDelta0    db '0.1', 0   

_Delta      dt 0
_Delta0     dt ?   
;.............................
                ;
                ; convert _sDelta0 to _Delta0
                ; »»»»»»»»»»»»»»»»»»»»»»»»»»»
                invoke  CvRclToRel, addr _sDelta0, addr _Delta0
                jc      _erro1
               
                ; -----------
                ; Test _Delta
                ; -----------
                fld     tbyte ptr _Delta0       ;st(1)
                fld     tbyte ptr _Delta        ;st(0)
                ;
                fcomip  st(0), st(1)
                fwait
                jpe     short _erro1
                ja      short _erro

                fstp    st                      ;remove source

                ; »»»»»»»»»»»»»»»»»
                ; EXIT  «««HERE !!!             ««««««««««««««««««««««
                ; »»»»»»»»»»»»»»»»»
                clc
                ret

    _erro1:     fstp    st                      ;remove source
                mov     eax, 1
                stc
                ret     

    _erro:      fstp    st                      ;remove source
                mov     eax, 0
                stc
                ret


[qWord]

have you tried to analyse it with OllyDbg? Also, testing for equality is not trivial.

BTW: fwait is not needed.

[raymond]

It is obvious that if you convert two identical strings with the same procedure, you will get identical results.

The procedure used by the assembler to convert your 0.1 string in the .data section is not necessarily identical to your own conversion procedure and could result in a small difference which could be picked up by the fcomip instruction. Using a debugger, look at the memory locations where the values are stored and compare their least significant bytes. Even if the difference is only 1, one would be considered larger than the other.

[RuiLoureiro]

qWord,

have you tried to analyse it with OllyDbg? Also, testing for equality is not trivial.

Thanks for reply
                I dont like to use it !
                I will go to use my converter to get _Delta0 before testing :wink
               

BTW: fwait is not needed.

Ok thanks  :U

[RuiLoureiro]

raymond,
          Thanks for reply

The procedure used by the assembler to convert your 0.1 string in the .data section
is not necessarily identical to your own conversion procedure and
could result in a small difference which could be picked up by the
fcomip instruction.

              The problem is the assembler converter, i think

              I also used your converter to convert the 0.1 string
              and it is not equal to that of .data section.
              In any case i solved the problem.