
1:106
Volume 1, Part 1: Floating-point Programming Model
then inexactness is signaled. If the significand was rounded by adding a one to its least
significant bit, then bit
fpa
in ISR.code is set to 1. Finally, an interruption due to a
Floating-Point Exception trap will occur.
Note that when rounding to single, double, or double-extended real, the overflow trap
enabled response for normal (non Parallel FP) arithmetic instructions is not guaranteed
to be in the range of a valid single, double, or double-extended real quantity, because it
is in 17-bit exponent format.
5.4.3
Definition of Tininess, Inexact and Underflow
Tininess
is detected after rounding, and is said to occur when a non-zero result
(computed as though the exponent range were unbounded) would lie strictly between
+2
Emin
and -2
Emin
. See
for the values of Emin for each real type. Creation of
a tiny result may cause an exception later (such as overflow upon division because it is
so small).
Inexactness
is said to occur when the result differs from what would have been
computed if both the exponent range and precision were unbounded.
How tininess and inexactness trigger the underflow exception depends on whether the
Underflow Floating-Point Exception trap is disabled or enabled. If the trap is disabled
then the underflow exception is signaled when the result is both tiny and inexact. If the
trap is enabled then the underflow exception is signaled when the result is tiny,
regardless of inexactness. Note that in the event that the Underflow Floating-Point
Exception trap is disabled and tininess but not inexactness occurs, then neither
underflow nor inexactness is signaled, and the result is a denormal.
The IEEE Underflow Floating-Point Exception trap disabled response for all normal and
Parallel-FP arithmetic instructions is to denormalize the infinitely precise result and then
round it to the destination precision. The result may be a denormal, zero, or a normal.
The inexact exception is signaled when appropriate.
The IEEE Underflow Floating-Point Exception trap enabled response for all normal
arithmetic instructions is to return the true biased exponent value MOD 2
17
and for all
Parallel-FP arithmetic instructions is to return the true biased exponent value MOD 2
8
.
The significand is rounded to the specified precision and written to the destination
register independent of the possibility of the exponent calculation requiring a borrow. If
the rounded value is different from the infinitely-precise value, then inexactness is
signaled. If the significand was rounded by adding a one to its least significant bit, then
bit
fpa
in ISR.code is set to 1. Finally, an interruption due to a Floating-Point Exception
trap will occur.
Note:
When rounding to single, double, or double-extended real, the underflow trap
enabled response for normal (non Parallel FP) arithmetic instructions is not
guaranteed to be in the range of a valid single, double, or double-extended real
quantity, because it is in 17-bit exponent format.
When Flush-to-Zero mode is enabled, the behavior for tiny results is different. If an
instruction would deliver a tiny result, a correctly signed zero is delivered instead and
the appropriate FPSR.sf
x
.u and FPSR.sf
x
.i bits are set. This mode may improve the
Содержание ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Страница 1: ......
Страница 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 12: ...1 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I Application Architecture Guide ...
Страница 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Страница 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Страница 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Страница 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Страница 230: ......
Страница 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 249: ...2 1 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part I System Architecture Guide ...
Страница 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Страница 380: ...2 132 Volume 2 Part 1 Interruptions ...
Страница 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Страница 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Страница 749: ...2 501 Intel Itanium Architecture Software Developer s Manual Rev 2 3 Part II System Programmer s Guide ...
Страница 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Страница 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Страница 808: ...2 560 Volume 2 Part 2 Context Management ...
Страница 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Страница 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Страница 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Страница 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Страница 891: ......
Страница 941: ...3 42 Volume 3 Instruction Reference cmp illegal_operation_fault PR p1 0 PR p2 0 Interruptions Illegal Operation fault ...
Страница 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Страница 1191: ...3 292 Volume 3 Pseudo Code Functions Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Страница 1296: ......
Страница 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Страница 1564: ...4 262 Volume 4 Base IA 32 Instruction Reference LES Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1565: ...Volume 4 Base IA 32 Instruction Reference 4 263 LFS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1568: ...4 266 Volume 4 Base IA 32 Instruction Reference LGS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1583: ...Volume 4 Base IA 32 Instruction Reference 4 281 LSS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Страница 1663: ...Volume 4 Base IA 32 Instruction Reference 4 361 SHL SHR Shift Instructions See entry for SAL SAR SHL SHR ...
Страница 1668: ...4 366 Volume 4 Base IA 32 Instruction Reference SIDT Store Interrupt Descriptor Table Register See entry for SGDT SIDT ...
Страница 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Страница 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Страница 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...