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Volume 1, Part 1: Floating-point Programming Model
5.4.1.3
Floating-point Exception Trap
A Floating-point Exception trap occurs if one of the following four circumstances arises:
1. The processor requests system software assistance to complete the operation, via
the Software Assist trap
2. The IEEE Overflow trap is enabled and an overflow occurs
3. The IEEE Underflow trap is enabled and an underflow occurs
4. The IEEE Inexact trap is enabled and an inexact result occurs
When an overflow, underflow, or inexact result occurs, the appropriate status flags are
updated in the FPSR. If enabled, a Floating-Point Exception trap occurs, and an
indication of which enabled trap occurred is stored in ISR.code and the fpa bit in
ISR.code (ISR{14}) is set as described in the next paragraph.
ISR.fpa is set to 1 when the magnitude of the delivered result is greater than the
magnitude of the infinitely precise result. It is set to 0 otherwise. The magnitude of the
delivered result may be greater if:
• The significand is incremented during rounding, or
• A larger pre-determined value (e.g., infinity) is substituted for the computed result
(e.g., when overflow is disabled).
There is no requirement that the Software Assist Floating-Point Exception trap ever be
signaled, nor is there a mode to force its use. In order to ensure maximum
floating-point performance, most implementations will not use this exception except in
difficult situations, such as operations creating denormal numbers. The occurrence of a
Software Assist trap is indicated when a trap bit is set in ISR.code, but that trap is
disabled. The destination register contains the trap enabled response for that trap.
The precedence among Floating-point Exception traps for arithmetic operations is
depicted in
.
Summary of Contents for ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Page 1: ......
Page 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Page 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Page 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Page 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Page 230: ......
Page 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Page 380: ...2 132 Volume 2 Part 1 Interruptions ...
Page 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Page 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Page 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Page 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Page 808: ...2 560 Volume 2 Part 2 Context Management ...
Page 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Page 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Page 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Page 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Page 891: ......
Page 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Page 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Page 1296: ......
Page 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...