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**Lance Edmonds** · 27 Feb 2001, 01:31 PM

Under what specific conditions does this occur?

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

**Chris Boss** · 27 Feb 2001, 01:52 PM

Lance;

When I call the PrintDlg function to displat the Printer Dialog
and then afterwards go through a standard procedure for printing .

After PrintDlg returns and that may be where the code hangs. So far the
code works fine on all platforms and all printers, except a few Listed
on a web page I found at the Microsoft web site (Epson Stylus and HP Laser 5L)
which exhibit this problem.

The PrintDlg function does load the default printer driver into
memory and as I said, the code works fine on most PC's and on all
Platforms (WIN95/98/NT/2000 Pro/ME). Its just the PC's with the suspect
printer drivers that cause the problem.

Is there any code (Basic or Assembler) I could execute after calling
PrintDlg, that would "reset" the Math Coprocessor so it would handle
exceptions the way the PB compiler expects it too ?

The cause is suppose to be because the printer driver changes the
settings for the math coprocessor and forgets to set it back when done.
If I could simply reset it myself in code, I wouldn't have to worry
about whether the printer driver did this.

I rechecked my code and actually I don't there is an immediate Floating point
code, but only Long (Integer) arithmetic. My code does though
retrieve values using GetDeviceCaps and then passes those values to
the API function DPtoLP ! It is possible this function does either
floating point or it may be dealing with division by zero or some
other exception.

It is possible that DPtoLP generates the exception, but only for
certain Printer drivers.

The exception error message does list my DLL as the offending DLL
though and not a system DLL, so it would seem my code causes the
exception though. The key here is that the code only causes an
exception with certain printer drivers.

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**Chris Boss** · 27 Feb 2001, 02:06 PM

Lance;

Actually, my code does do some floating point match shortly after
calling PrintDlg !

The floating point math is in some procedures I call just before
executing StartDoc. I display an Abort Dialog and the procedures
that generate this dialog use some floating point for conversion
of coordinates.

The main point is that the problem seems to occur between the
PrintDlg function call and before StartDoc gets executed. The abort
Dialog doesn't display as far as I know, so the floating point math
could be crashing the app, after the PrintDlg call, if the printer
drivers really do exhibit the problem as stated by Microsoft.

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**Daniel Corbier** · 27 Feb 2001, 04:39 PM

chris, i think i've encountered a problem like this with my
product. it was very difficult to track, because only a few
people had this problem, and i couldn't duplicate it on my
own system. in search for a solution though i read a document
which talked about printer drivers which mess up the fpu. this
might be the same document you are talking about.

my temporary solution was to tell the users to add the following
lines in their c++ builder code.

Code:

#include <float.h>
_fpreset();
_control87(mcw_em, mcw_em);

i've had only a couple of people report this problem, and they
happpened to be using c++. i don't know how you'd do something
like that in pb itself. even if this problem is not caused by
pb, i do hope that pb will add the _fpreset() and
_control87() functions.

by the way, there was another thread where i mentioned this
problem. see bizarre math bug
however, there were several other problems which were also
discussed, and i'm not sure that this particular one was
resolved in that discussion.

------------------
daniel corbier
ucalc fast math parser
http://www.ucalc.com

[this message has been edited by daniel corbier (edited february 27, 2001).]

**Chris Boss** · 27 Feb 2001, 08:36 PM

From the reports I am receiving from a number of Beta testers,
the problem is definitely associated with Printer drivers.

In one situation the Beta tester, replaced his printer driver with
a new version and the problem disappeared.

It would seem that if I could do what Daniel suggests (but using PB code)
after I call the PrintDlg function, the problem would be solved.

I need to find a way to "reset" the FPU (floating point processor)
so my PB floating point code won't crash.

Are there any assembler programmers out there who could show us
how to reset the FPU using assembler ?

Would it be possible to do this with straight Basic code (with
API calls) as well ?

How would we convert Daniels C code :

Code:

#include <float.h>
_fpreset();
_control87(MCW_EM, MCW_EM);

to PB code ?

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**Chris Boss** · 27 Feb 2001, 09:22 PM

Question :

Would it be possible to use ON ERROR GOTO to reset the
FPU ?

By using an ON ERROR GOTO after the PrintDlg function call and then
doing some floating point math just to trip the exception, could this work ?

I would assume that ON ERROR GOTO likely uses some exception handling
(would that be correct ?) .

Does On ERROR do exception handling ?

Would this be useful in reseting the FPU ?

I am just guessing here, so could someone enlighten me ?

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**Borje Hagsten** · 28 Feb 2001, 12:41 AM

#register none ?

found the following doc in faq via poffs:

'message http://www.powerbasic.com/support/pb...hread.php?t=45
'forum: frequently asked questions
'topic: win32: extended-precision and quad integer math (pb/cc 1.0, 2.0 and pb/dll 5.0, 6.0)
'name: lance edmonds, administrator
'date: january 14, 2000 03:29 am

.. no need to repeat the above - see link.

[this message has been edited by borje hagsten (edited february 28, 2001).]

**Lance Edmonds** · 28 Feb 2001, 03:02 AM

I would be very surprised if #REGISTER NONE had *anything* to do with Chris' printer driver problems.

Similarly, the 54-bit precision issue is not likely to cause a FPU exception.

My suspicions are that the cause of the problem is not a coprocessor exception, but some other problem (such as memory corruption) - probably in the printer driver...

ON ERROR works by inserting code into the EXE that tests for run-time error conditions after each "line" of code is executed. An ON ERROR trap is not able to catch an O/S level exception, page fault, or GPF. If #DEBUG ERROR ON is used, then the compiler does add code to test for nul-pointers and array bounds violations.

The request for more powerful exception handling is already on the "wish list"

------------------
Lance
PowerBASIC Support
mailto:[email protected][email protected]</A>

**Guest** · 28 Feb 2001, 05:27 AM

> #include <float.h>
> _fpreset();
> _control87(MCW_EM, MCW_EM);

Code:

These can be used by PB.  Declare the functions using Alias.  They
are in the msvcrtXX series of dlls.  Try msvcrt20.dll.
 
Declare Sub fpreset Cdecl Lib "msvcrt20.dll" Alias "_fpreset" ()
Declare Sub control87 Cdecl Lib "msvcrt20.dll" Alias "_control87" ( Dword new, Dword Mask )
 
   /* Show original control word and do calculation. */
   printf( "Original: 0x%.4x\n", _control87( 0, 0 ) );
   printf( "%1.1f * %1.1f = %.15e\n", a, a, a * a );
   /* Set precision to 24 bits and recalculate. */
   printf( "24-bit:   0x%.4x\n", _control87( _PC_24, MCW_PC ) );
   printf( "%1.1f * %1.1f = %.15e\n", a, a, a * a );
   /* Restore to default and recalculate. */   
   printf( "Default:  0x%.4x\n", _control87( _CW_DEFAULT, 0xfffff ) );
   printf( "%1.1f * %1.1f = %.15e\n", a, a, a * a );

[This message has been edited by Ron Pierce (edited February 28, 2001).]

**Chris Boss** · 28 Feb 2001, 06:15 AM

If you go to the MSDN web site and do a search for the words :

Exception 10H

You will find a number of pages that refer to the printer drivers
being the cause of the problem !

Fact #1 The Printer Drivers are the likely cause of this problem.
The only time this Exception is generated by my code is when a suspect
printer driver was in use. The few times the error occured, the printer
drivers in use were ones listed on the following web page as suspect:

http://support.microsoft.com/support.../Q141/9/30.asp

Next, when you examine a few of those web pages that explain what
the Exception 10H means, you come to the conclusion that the FPU
is definitely involved.

http://support.microsoft.com/support.../Q150/3/14.asp

http://support.microsoft.com/support.../Q117/3/89.asp

Fact #2 The 10H Exception means : Coprocessor Error Fault
and this Exception is generated by Floating point math (when the right
circumstances are set).

There should be some way to "reset" the math coprocessor to avoid
this problem.

There should be some way to emulate Daniels suggested C code with
PB code (or ASM) :

Code:

#include <float.h>
_fpreset();
_control87(MCW_EM, MCW_EM);

without resorting to making a call into a Microsoft C runtime DLL.

How about you Assembler experts out there ?

Can you show us the code in ASM ?

[This message has been edited by Chris Boss (edited February 28, 2001).]

**Chris Boss** · 28 Feb 2001, 08:07 AM

I decided to follow Ron's suggestion and I did a test:

I made the two calls into the msvcrt20.dll as he suggested, right
after executing PrintDlg.

The results :

A Beta tester who found had a problem with multiple printer drivers
(some worked and some didn't) says the problem is now gone !.

Code:

%MCW_EM         =   &H1f???
DECLARE SUB fpreset CDECL LIB "msvcrt20.dll" ALIAS "_fpreset" ()
DECLARE SUB control87 CDECL LIB "msvcrt20.dll" ALIAS "_control87" ( BYVAL NewVal AS DWORD, BYVAL MaskVal AS DWORD)

Code:

' used this code after calling PrintDlg
fpreset
control87 %MCW_EM, %MCW_EM

The PB code above eliminates the Exception generated by floating
point calculations after calling PrintDlg.

Now, I need to convert the two C calls into PB code using assembler !

I examined the FPU Instruction set and the only instructions that
would seem to accomplish what I want are :

FINIT (Initialize the FPU after checking error condition)
FNINIT (same but no error checking)

FCLEX (Clear Floating point exception flags after error checking)
FNCLEX (same but no error checking)

FLDCW address (Load Control Register Status)
FSTCW address (Store Control Register Status)

It would seem that the function call fpreset is likely just
the FNINIT instruction.

Since control87 uses parameters (a value and a mask), it is likely
multiple instructions likely using FLDCW and FSTCW !

This is where I need some help from an assembler expert !

------------------

**Tom Hanlin** · 28 Feb 2001, 11:31 AM

I suspect that changing the state of the FPU is likely to be similar to
changing CPU registers at random-- the effects won't be pretty. This is
not clearly safe to play with. Let me see what R&D has to say.

------------------
Tom Hanlin
PowerBASIC Staff

**Chris Boss** · 28 Feb 2001, 12:01 PM

The following assembler instructions seem the most likely to
be the ones used by _control87 :

FLDCW address (Load Control Register Status)
FSTCW address (Store Control Register Status)

The following assembler instructions seem the most likely to
be the ones used by _fpreset :

FINIT (Initialize the FPU after checking error condition)
FNINIT (same but no error checking)

Tom;

There seems to be no other way to solve this problem !
The printer driver is likely changing the FPU Control Word's
Exception Mask Flags and when PB code attempts any Floating point
calculations, the 10h Exception is generated (or worse).

As long as the FPU control word is set to something "acceptable" to
how PB handles Floating point calculations, there shouldn't be a
problem. The problem is, I don't know what PB expects as far as the
FPU Control Word !

Any suggestions from R&D would be appreciated.

As a side thought, Powerbasic should consider adding its own
versions of _fpreset and _control87 . _control87 is a very useful
tool for controlling how the FPU handles certain things. You can
set things like the precision, rounding, exception maskes, ect. with
it.

All the Windows C compilers have these commands in their libraries.

------------------

**Tom Hanlin** · 28 Feb 2001, 12:29 PM

According to R&D, it is not safe to fiddle with the FPU status using
assembly language. Doing so could cause a variety of undesireable side-effects.

There is another way to resolve the problem: replace the buggy printer
driver. Without knowing exactly what the driver is doing wrong, there can be
no reliable work-around in your program anyway. Bear in mind that the printer
driver functions asynchronously with respect to your program.

I'll add a second tick to _fpreset and _control87 on the wish list.

------------------
Tom Hanlin
PowerBASIC Staff

**Cecil Williams** · 28 Feb 2001, 01:00 PM

Chris,

As Ron pointed out, these functions are located in the
msvcrtxx.dll files. I have NT4 on my machine and the following
versions are listed in system32 subdirectory:

msvcrt.dll
msvcrtd.dll
msvcrt20.dll
msvcrt40.dll

All these dll's have the functions in question. I would recommend
doing a "runtime" load of the various dll's and check for a return
on LoadLibrary and use the one that returns non-NULL. Then get
the procedure address and make the calls.

Cheers,
Cecil

------------------

**Chris Boss** · 28 Feb 2001, 01:03 PM

Tom;

It doesn't make much sense that most C compilers have the
_control87 procedure (which does fiddle with the FPU status)
if it was so dangerous.

I would assume that when the operating system switches between
threads, it would save the status of the FPU for each thread,
otherwise the OS would be very unstable running multiple threads.

------------------

**Chris Boss** · 28 Feb 2001, 01:05 PM

Tom;

How about if I Save the status of the FPU from before calling
the PrintDlg function and then restore it to the same values after
the PrintDlg function returns ?

This would seem safe to me.

------------------

**Bern Ertl** · 28 Feb 2001, 01:12 PM

Chris,

What happens if another app access the printer driver either
before or after your app does? It doesn't seem to me that you can
ever be sure that the settings are correct if the printer driver
can screw it up on a moments notice.....

------------------
Bernard Ertl

**Chris Boss** · 28 Feb 2001, 01:44 PM

Here is an interesting discussion of the very samme problem on a
News group :

http://groups.google.com/groups?hl=e...4524#949454524

A number of programmers "do" fiddle with the FPU state to solve
problems !

Likely a number apps either don't use floating point calculations
so they don't exhibit this problem with print drivers. Likely others
take defensive steps and they do fiddle with the FPU states after
making some function calls.

The HP drivers (which many end users have) seem to be the most
notorious for this problem.

I would appreciate any suggestions from anyone with experience
dealing with this kind of problem.

While the easiest solution is to simply tell people to get a new
printer driver, there are likely some printers that do not have
driver updates. If I can fiddle with the FPU state safely (only after the
PrintDlg call) to prevent the problem (which has been demonstrated
to work), this would seem a better solution to me.

Are there any assembler experts out there who could write a simple
(smart and as safe as possible) FPU reset function ?

------------------

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