Microsoft KB Archive/152056

= BUG: Using Intrinsic Versions of log10 and fmod =

Article ID: 152056

Article Last Modified on 12/10/2003

-

APPLIES TO


 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 4.1 Subscription
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Professional Edition

-



This article was previously published under Q152056



SYMPTOMS
In some cases, using the intrinsic versions of log10 and fmod together in a program may produce incorrect results. The sample code below illustrates the problem.

When the result of log10 is a negative whole number that is divided by 1.0 using fmod, the result of fmod will be -1.0 rather than 0.0. This only occurs when the compiler generates the intrinsic versions of these functions. You need to use the /Oi compiler option to have the compiler generate intrinsic versions of functions.



RESOLUTION
When using log10 and fmod together in a function, as in the sample code, do not use the /Oi compiler option.



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.



Sample Code
/* Compile options needed: /Oi */   #include    #include 

void main {      double dValue, theLog, theMod;

dValue = 0.01; theLog = log10( dValue ); theMod = fmod( theLog, 1.0 );

printf( "The log10 of %f is %f\n", dValue, theLog ); printf( "The fmod of (%f,1.0) is %f\n", theLog, theMod ); printf( "for all x, fmod(x, 1.0) should always be 0.0\n" ); }

Additional query words: kbVC400bug

Keywords: kbbug kbcodegen kbcompiler KB152056

-

[mailto:TECHNET@MICROSOFT.COM Send feedback to Microsoft]

© Microsoft Corporation. All rights reserved.