Release 1.0, 1 July 2002
F. Chapter B
IEEE Std 754-1985 Requirements for SPARC V9
63
Implementation Note –
Detecting the exact boundary conditions requires a large
amount of hardware. SPARC64 V detects approximate boundary conditions by
calculating the exponent intermediate result (the exponent before rounding) from
input operands, to avoid the hardware cost. Since the computation of the boundary
conditions is approximate, the detection of a zero result or an overflow result shall
be pessimistic. SPARC64 V generates an
unfinished_FPop
exception pessimistically.
The equations to calculate the result exponent to detect the boundary conditions
from the input exponents are presented in
TABLE B-1
, where Er is the approximation
of the biased result exponent before rounding and is calculated only from the input
exponents (esrc1, esrc2). Er is to be used for detecting the boundary condition for an
unfinished_FPop
.
esrc1 and esrc2 are the biased exponents of the input operands. When the
corresponding input operand is a denormalized number, the value is 0.
From Er, eres is calculated. eres is a biased result exponent, after mantissa alignment
and before rounding, where the appropriate adjustment of the exponent is applied to
the result mantissa: left-shifting or right-shifting the mantissa to the implicit 1 at the
left of the binary point, subtracting or adding the shift-amount to the exponent. The
result mantissa is assumed to be 1.xxxx in calculating eres. If the result is a
denormalized number, eres is less than zero.
TABLE B-2
describes the boundary condition of each floating-point instruction that
generates an
unfinished_FPop
exception.
TABLE B-1
Result Exponent Approximation for Detecting
unfinished_FPop
Boundary
Conditions
Operation
Formula
fmuls
Er = esrc1 + esrc2
−
126
fmuld
Er = esrc1 + esrc2
−
1022
fdivs
Er = esrc1 - esrc2 + 126
fdivd
Er = esrc1 - esrc2 + 1022
TABLE B-2
unfinished_FPop
Boundary Conditions
Operation
Boundary Conditions
FdTOs
−
25 < eres < 1 and
TEM.UFM
= 0.
FsTOd
Second operand (
rs2
) is a denormalized number.
FADDs
,
FSUBs
,
FADDd
,
FSUBd
1. One of the operands is a denormalized number, and the other operand is a normal,
nonzero floating-point number (except for a NaN and an infinity)
1
.
2. Both operands are denormalized numbers.
3. Both operands are normal nonzero floating-point numbers (except for a NaN and
an infinity), eres < 1, and
TEM.UFM
= 0.
Summary of Contents for SPARC JPS1
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Page 118: ...F APPENDIX 107 G Assembly Language Syntax Please refer to Appendix G of Commonality ...
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Page 120: ...F APPENDIX 109 H Software Considerations Please refer to Appendix H of Commonality ...
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Page 124: ...F APPENDIX 113 J Changes from SPARC V8 to SPARC V9 Please refer to Appendix K of Commonality ...
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Page 126: ...F APPENDIX 115 K Programming with the Memory Models Please refer to Appendix J of Commonality ...
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Page 234: ...223 F CHAPTER Bibliography General References Please refer to Bibliography in Commonality ...
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