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1994-01-07
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DOCUMENT:Q93353 06-JAN-1994 [W_NT]
TITLE :INF: 80x87 Floating Point Emulation Under Windows NT
PRODUCT :Windows NT
PROD/VER:3.10
OPER/SYS:WINDOWS
KEYWORDS:
--------------------------------------------------------------------
The information in this article applies to:
- Microsoft Windows NT operating system version 3.1
--------------------------------------------------------------------
SUMMARY
=======
The math emulator provided by the Windows NT kernel is intended to
provide emulation of 80387 floating-point instructions. However, only
ANSI floating-point precision is provided. Long double precision is
not emulated. This is consistent with MIPS (millions of instructions
per second) architecture.
Some other minor differences are known and may remain in the final
version. For example, tests on the 80387 chip revealed that the FSAVE
instruction leaves the Error Offset and Error Selector fields in the
FP environment block null if there are no pending exceptions. The
Windows NT emulator fills these fields with the address of the most
recently emulated instruction, even when no exception is pending. This
behavior may remain because it provides extra information to the
system programmer and because the emulator status word accurately
indicates any pending exceptions.
MORE INFORMATION
================
The information applies to Win32s as well.
The floating point emulator does not support CS overrides. This does not
effect compiler-generated code, only hand-tuned assembly code. This was
done to improve speed, since applications that were written in C are not
affected.
Additional reference words: 3.10
=============================================================================
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.
Copyright Microsoft Corporation 1994.