Q126882 - Visual C++ sin(), cos(), and tan() Incorrect w/ 287

Visual C++ sin(), cos(), and tan() Incorrect w/ 287

Q126882

The information in this article applies to:

The C Run-Time (CRT), used with:
- Microsoft Visual C++, versions 1.0, 1.5, 1.51, 1.52

SUMMARY

Calls to the sin(), cos(), or tan() in a program built with the Visual C++ versions listed at the beginning of this article return incorrect results. This is caused by a bug in the Visual C++ run-time (CRT) functions. The functions have a problem with 287 synchronization on 80286 systems with 80287 coprocessors. The timing problem does not affect programs running on an 80386 with an 80387 coprocessor, on an 80486, or on a Pentium processor. You can get a patch (VC287P.EXE) to fix a bug that occurs with the sin(), cos(), and tan() run-time functions. These functions return incorrect values when a program built with Visual C++ is run on a computer that has both an 80286 processor and an 80287 math coprocessor.

The following files are available for download from the Microsoft Download Center:

Vc287p.exe

For additional information about how to download Microsoft Support files, click the article number below to view the article in the Microsoft Knowledge Base:

Q119591 How to Obtain Microsoft Support Files from Online Services

Microsoft used the most current virus detection software available on the date of posting to scan this file for viruses. Once posted, the file is housed on secure servers that prevent any unauthorized changes to the file.

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was corrected in the patch announced in this article.

MORE INFORMATION

Please note that this patch is a partially tested fix for this problem. No problems have been detected with it, however it has not gone through a full product test cycle. Microsoft makes no guarantees for its useability or functionality. See the LEGAL.TXT included with the patch for more details.

The patch also contains a README.TXT with installation details and the information in this article.

Sample Code to Reproduce Problem


   /* Compile options needed: None
   */ 
   #include <math.h>
   #include <stdio.h>
   #include <stdlib.h>

   void main(void)
   {
      double x;

      x=1.0;
      printf( "cos(x) = %lf, sin(x) = %lf, tan(x) = %lf, x = %lf\n",
              cos(x), sin(x), tan(x), x );
   }

Results

The following correct output was produced on a 286/287 with NO87=1:


   cos(x) = 0.540302, sin(x) = 0.841471, tan(x) = 1.557408, x = 1.000000

The following incorrect output was produced on a 286/287 with NO87 not set:


   cos(x) = 1.000000, sin(x) = 2.000000, tan(x) = 0.000000, x = 1.000000

Additional query words:

Keywords : kbfile kbhw kbprogramming kb16bitonly kbCRT kbVC
Issue type :
Technology : kbVCsearch kbAudDeveloper kbCRT