inter
OVERVIEW OF NUMERIC PROCESSING
Table 1-16.
Temporary
Real
Encodings
(Cont'd.)
Class Sign
Biased
Significand·
Exponent
l,:lff
...
ff
00
1
11
...
11
100
...
00
1
11
...
11
100
...
00
·
· ·
·
· ·
III
Q)
·
· ·
iii
Cl
Indefinite 1
11
...
11
110
...
00
Q)
z
·
0 0
·
· ·
· · ·
1
11
...
11
111
...
11
1..--15
bits ---.11-4
..
---
64
bits
Numeric Exceptions
Whenever the 80287
NPX
attempts a numeric operation with invalid operands or produces a result
that
cannot be represented, the 80287 recognizes a numeric exception condition. Altogether, the 80287
checks for the following six classes of exceptions while executing numeric instructions:
1.
Invalid operation
2.
Divide-by-zero
3.
Denormalized operand
4.
Numeric overflow
5.
Numeric underflow
6.
Inexact result (precision)
INVALID OPERATION
The 80287 reports an invalid operation if any of the following occurs:
• An attempt to load a register that
is
not empty (stack overflow).
• An attempt to pop an operand from an empty register (stack underflow).
• An operand
is
a
NaN.
• The operands cause the operation to be indeterminate (square root of a negative number,
0/0).
An invalid operation generally indicates a program error.
ZERO DIVISOR
If
an instruction attempts to divide a finite nonzero operand by zero, the 80287 will report a zero divide
exception.
1-33
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