FUJITSU Implementation Supplement Fujitsu SPARC64 V - Manual (Page 76)

Release 1.0, 1 July 2002 F. Chapter B IEEE Std 754-1985 Requirements for SPARC V9 65
Pessimistic Overflow
If a condition in TABLE B-4 is true , SPARC64 V regards the operation as having an
overflow condition.
B.6.2 Operation Under FSR.NS = 1
When FSR.NS = 1 (nonstandard mode), SPARC64 V zeroes all the input
denormalized operands before the operation and signals an inexact exception if
enabled. If the operation generates a denormalized result, SPARC64 V zeroes the
result and also signals an inexact exception if enabled. The following list defines the
operation in detail.
■ If either operand is a denormalized number and both operands are non-zero, non-
NaN, and non-infinity numbers, the input denormalized operand is replaced with
a zero with same sign, and the operation is performed. If enabled, inexact
exception is signalled; an
fp_exception_ieee_754 ( tt = 021
16
) is generated, with
nxc =1 in FSR.cexc ( FSR.ftt =01
16
; IEEE754_exception ). However, if the
operation is FDIV ( s,d ) and either a division_by_zero or an invalid_operation
condition is detected, or if the operation is FSQRT ( s,d ) and an invalid_operation
condition is detected, the inexact condition is not reported.
■ If the result before rounding is a denormalized number, the result is flushed to a
zero with a same sign and signals either an underflow exception or an inexact
exception, depending on
FSR.TEM .
As observed from the preceding, when FSR.NS = 1, SPARC64 V generates neither
an unfinished_FPop exception nor a denormalized number as a result. TABLE B-5
TABLE B-3 Conditions for a Pessimistic Zero
Operations
Conditions
One operand is denormalized 1
1. Both operands are non-zero, non-NaN, and non-infinity numbers.
Both are denormalized Both are normal fp-number 2
2. Both may be zero, but both are non-NaN and non-infinity numbers.
FdTOs always — eres
≤
-25
FMULs ,
FMULd
single precision: Er ≤ − 25
double precision: Er ≤ − 54
Always single precision: eres ≤ − 25
double precision: eres ≤ − 54
FDIVs ,
FDIVd
single precision: Er
≤ −
25
double precision: Er
≤ −
54
Never single precision: eres
≤ −
25
double precision: eres
≤ −
54
TABLE B-4 Pessimistic Overflow Conditions
Operations Conditions
FDIVs The divisor (operand2; rs2) is a denormalized number and, Er
≥
255.
FDIVd The divisor (operand2; rs2) is a denormalized number and, E ≥ 2047.