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Report From: Delphi-BCB/RTL/Delphi/Math Unit [ Add a report in this area ]

Report #: 81203

Status: Closed

RoundTo clear fpu exception mask

Project: Delphi

Build #: 14.0.3593.25826

Version: 14.0

Submitted By: Roman Kolesnikov

Report Type: Crash / Data loss / Total failure

Date Reported: 1/15/2010 1:41:24 AM

Severity: Commonly encountered problem

Last Updated: 3/20/2012 2:24:39 AM

Platform: All platforms

Internal Tracking #: 274504

Resolution: Fixed (Resolution Comments)

Resolved in Build: : 16.0.4256.43595

Duplicate of: None

Voting and Rating

Overall Rating: (1 Total Rating)

3.00 out of 5

Total Votes: 2

Description

Bug in RoundTo function
it crashes if FPU exceptions are disabled by Set8087CW($133F);

error is in line
fldcw   word ptr [CW8087X] - it clears fpu exception mask flags

to set fpu controls flags you shoud use code like that in function Trunc in system.pas
        FNSTCW  [ESP].Word          // save
        FNSTCW  [ESP+2].Word        // scratch
        FWAIT
        OR      [ESP+2].Word, $0F00  // trunc toward zero, full precision
        FLDCW   [ESP+2].Word

Steps to Reproduce:

var
  x, y: Double;
begin
  Set8087CW($133F);
  x := 0.0;
  y := 5 / x;
  if y <> -100 then
    RoundTo(1.23, -1);
end;

Workarounds

None

Attachment

None

Comments

Tomohiro Takahashi at 1/17/2010 5:56:23 PM -

Could you please attach sample project to understand your issue about RoundTo?
With you code block, this line causes EZeroDevide execption...
> y := 5 / x;

Alexander Alexeev at 1/18/2010 12:29:19 AM -

>>> With you code block, this line causes EZeroDevide execption...
This line do not generate exception, as exceptions are disabled by the above call to Set8087CW!

Create a new empty VCL application and insert this code into Button1.OnClick event handler.

Tomohiro Takahashi at 1/18/2010 5:14:24 AM -

Indeed, RoundTo has the problem at least Delphi 2009, 2010 ...

Alexander Alexeev at 1/18/2010 12:26:36 AM -

Possible related report: 79714

Roman Kolesnikov at 9/21/2011 12:38:33 AM -

Fixed in XE2

Tomohiro Takahashi at 9/21/2011 8:15:42 AM -

Thanks for the confirmation. I will check the internal status of this report.

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