Intel387
TM
SX MATH COPROCESSOR
APPENDIX A
INTEL387 SX MATH COPROCESSOR
COMPATIBILITY
A.1 8087/80287 Compatibility
This section summarizes the differences between the Intel387 SX Math CoProcessor and the 80287 Math
CoProcessor. Any migration from the 8087 directly to the Intel387 SX Math CoProcessor must also take into
account the differences between the 8087 and the 80287 Math CoProcessor as listed in Appendix B.
Many changes have been designed into the Intel387 SX Math CoProcessor to directly support the IEEE
standard in hardware. These changes result in increased performance by eliminating the need for software
that supports the standard.
A.1.1 GENERAL DIFFERENCES
The Intel387 SX Math CoProcessor supports only affine closure for infinity arithmetic, not projective closure.
Operands for FSCALE and FPATAN are no longer restricted in range (except for
g
%
); F2XM1 and FPTAN
accept a wider range of operands.
Rounding control is in effect for FLD constant.
Software cannot change entries of the tag word to values (other than empty) that differ from actual register
contents.
After reset, FINIT, and incomplete FPREM, the Intel387 SX Math CoProcessor resets to zero the condition
code bits C
3
–C
0
of the status word.
In conformance with the IEEE standard, the Intel387 SX Math CoProcessor does not support the special data
formats pseudo-zero, pseudo-NaN, pseudo-infinity, and unnormal.
The denormal exception has a different purpose on the Intel387 SX Math CoProcessor. A system that uses the
denormal exception handler solely to normalize the denormal operands, would better mask the denormal
exception on the Intel387 SX Math CoProcessor. The Intel387 SX Math CoProcessor automatically normalizes
denormal operands when the denormal exception is masked.
A-1
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