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Q128895: PRB: LNK2001 Link Error on Floating Division Functions

Article: Q128895
Product(s): Microsoft C Compiler
Version(s): 2.10
Operating System(s): 
Keyword(s): kbCRT kbVC kbprb
Last Modified: 29-JUL-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- The C/C++ Compiler (CL.EXE), included with:
   - Microsoft Visual C++, 32-bit Editions, version 2.1 
-------------------------------------------------------------------------------

SYMPTOMS
========

Compiling a program containing floating point divisions and linking with
run-time libraries other than those supplied with Microsoft Visual C++ version
2.1 can result in LNK2001 unresolved external errors on the following
functions:

  __adj_fdiv_m32
  __adj_fdiv_m64
  __adj_fdivr_m64
  __adjust_fdiv

This can occur when linking to libraries such as CRTDLL.LIB or the run-time
libraries that came with Microsoft Visual C++ version 2.0.

CAUSE
=====

The compiler and libraries that ship with Microsoft Visual C++ version 2.1
provide a method of avoiding Pentium division instructions. Pentium division
instructions can generate inaccurate results in some cases. The compiler inserts
calls to emulation functions instead of inserting floating point processor
instructions. These floating point division emulation functions are in the
run-time libraries shipped with version Visual C++ version 2.1, but not with
earlier versions of the libraries.

RESOLUTION
==========

The libraries and compiler that come with Microsoft Visual C++ version 2.1 are
designed to work together. If other libraries must be used, use the following
compiler switch to force insertion of floating point processor instructions
instead of inserting calls to the emulation functions:

  /QIfdiv-          {use coprocessor instead of calls to functions}

STATUS
======

This behavior is by design.

MORE INFORMATION
================

The sample code below will generate the following four errors if the LIB
environment variable is pointing to the Visual C++ version 2.0 libraries:

  error LNK2001: unresolved external symbol "__adj_fdiv_m32"
  error LNK2001: unresolved external symbol "__adj_fdiv_m64"
  error LNK2001: unresolved external symbol "__adj_fdivr_m64"
  error LNK2001: unresolved external symbol "__adjust_fdiv"

Using the compile option "/QIfdiv-" will prevent the references to these
functions.

For information about a related issue on Pentium floating point functions, please
see the following article in the Microsoft Knowledge Base:

  Q128148 Procedure Entry Point fdiv Not Located in MSVCRT20.DLL

Sample Code
-----------

  /* Compile options needed: none
     Environment needed    : set LIB point to a directory with the VC++
                             2.0 libraries
  */ 

  void main(void) {
     double x=1.2,z;
     float y=2.1;
     z=x/y;
     x=x/z;
     x=1/z;
  }

Additional query words: 2.10 2.00 2.55 9.10

======================================================================
Keywords          : kbCRT kbVC kbprb 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : 2.10
Issue type        : kbprb

=============================================================================

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