ID Number: Q32865
5.00 5.10 5.10a 6.00 6.00a 6.00b| 5.10 5.10a 6.00 6.00a 6.00b
MS-DOS | OS/2
Summary:
A good source of information for the 80287 Control and Status Words
is the INTEL 80286 and 80287 Programmer's Reference Manual. The text
below gives a brief summary of the information found in the INTEL
reference concerning the Invalid Operation and Inexact Result
exceptions.
More Information:
When the 80287 processor attempts a numeric operation with invalid
operands or produces a result that cannot be represented, the
processor will check certain numeric exceptions. Among the exceptions
checked are Invalid Operation and Inexact Result.
The 80287 reports an Invalid Operation if any of the following occurs:
An attempt to load a register that is not empty (stack overflow).
-or-
An attempt to pop an operand from an empty register (stack underflow).
-or-
An operand is a NaN.
-or-
The operands cause the operation to be indeterminate (square root
of negative number,0/0).
If the result of an operation is not exactly representable in the
destination format, the 80287 rounds the number and reports the
precision exception. For example, the fraction 1/3 cannot be precisely
represented in binary form.
The 80287's system of real numbers may be closed by either two models
of infinity. The two models are projective and affine closure. The
default means of closure is projective. When projective closure is
selected, the NPX treats the special values +infinity and -infinity as
a single unsigned infinity. In the affine mode, the NPX respects the
signs of infinity. While affine mode may provide more information than
projective mode, there are occasions when the sign may be misleading.
Projective mode, on the other hand, provides less information, but
will not be misleading.