Sun Microelectronics
242
UltraSPARC User’s Manual
and is incremented for each all-layer mask revision. The minor number
starts at zero for each major revision, and is incremented for each less-
than-all-layer mask revision.
maxtl: Maximum number of supported trap levels beyond level 0. This is the
same as the largest possible value for the TL register. For UltraSPARC,
maxtl=5.
maxwin: Maximum index number available for use as a valid CWP value. The
value is NWINDOWS–1; for UltraSPARC maxwin=7.
14.3 SPARC-V9 Floating-Point Operations
14.3.1 Subnormal Operands & Results; Non-standard Operation
UltraSPARC handles some cases of subnormal operands or results directly in
hardware and traps on the rest. In the trapping cases, an
fp_exception_other
(with
FSR.ftt=2,
unfinished_FPop
) trap is signalled and these operations are handled in
system software. The unfinished trapping cases are listed in Table 14-4, and
Table 14-5.
Because trapping on subnormal operands and results can be quite costly,
UltraSPARC supports the non-standard result option of the SPARC-V9 architec-
ture. If FSR.NS = 1, subnormal operands or results encountered in trapping cases
are flushed to zero and the
unfinished_FPop
floating-point trap type are not taken.
14.3.1.1 Subnormal Operands
If FSR.NS=1, the subnormal operands of these operations are replaced by zeroes
with the same sign. An inexact exception is signalled in this case, which causes
an
fp_exception_ieee_754
trap if enabled by FSR.TEM. If FSR.NS=0, subnormal op-
erands generate traps according to Table 14-4 on page 243. E
R
is the biased expo-
nent of the result before rounding.
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