Knowledge Base

BUG: Some Compiler and Debugger REAL Arithmetic Results Differ

PSS ID Number: 149157

Article Last Modified on 11/2/1999

The information in this article applies to:

Microsoft Fortran PowerStation for Windows 95 and Windows NT 4.0

This article was previously published under Q149157

SYMPTOMS

The results of some REAL double-precision arithmetic expressions generated by the compiler are different in the low order decimal digits from what is displayed for the same arithmetic expressions in the debugger.

CAUSE

Intermediate values in the debugger are saved to and reloaded from the stack. The saving and reloading of these intermediate values causes some rounding to occur.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Problem

Build a project containing the following sample code:

C Compile options needed: /Zi

      real*8  A, B, C, D

      A = 100.92
      B = -82.73
      C = -17.29
      D = 4.0

      write (*,*) (((-C)**D)+((A*D)/B))

      end

From the Developer Studio Build menu, choose Debug, and then select Step Into to begin the debugging process.
Step past the "write" statement.
In either the watch or quickwatch window, type the following arithmetic expression and press the ENTER key:
(((-C)**D)+((A*D)/B))
View the debugger and program output.

Output

From the debugger: 89362.714366112600000

Program execution: 89362.714366112590000

Additional query words: 4.00

Keywords: kbLangFortran KB149157
Technology: kbAudDeveloper kbFORTRANPower400NT kbFortranSearch kbZNotKeyword8