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Volume 4: Base IA-32 Instruction Reference
FUCOM/FUCOMP/FUCOMPP—Unordered Compare Real
Description
Performs an unordered comparison of the contents of register ST(0) and ST(i) and sets
condition code flags C0, C2, and C3 in the FPU status word according to the results (see
the table below). If no operand is specified, the contents of registers ST(0) and ST(1)
are compared. The sign of zero is ignored, so that -0.0 = +0.0.
An unordered comparison checks the class of the numbers being compared (see
). The FUCOM instructions perform the same
operation as the FCOM instructions. The only difference is that the FUCOM instruction
raises the invalid-arithmetic-operand exception (#IA) only when either or both
operands is an SNaN or is in an unsupported format; QNaNs cause the condition code
flags to be set to unordered, but do not cause an exception to be generated. The FCOM
instruction raises an invalid-operation exception when either or both of the operands is
a NaN value of any kind or is in an unsupported format.
As with the FCOM instructions, if the operation results in an invalid-arithmetic-operand
exception being raised, the condition code flags are set only if the exception is masked.
The FUCOMP instructions pop the register stack following the comparison operation and
the FUCOMPP instructions pops the register stack twice following the comparison
operation. To pop the register stack, the processor marks the ST(0) register as empty
and increments the stack pointer (TOP) by 1.
Operation
CASE (relation of operands) OF
ST > SRC:
C3, C2, C0
000;
ST < SRC:
C3, C2, C0
001;
ST = SRC:
C3, C2, C0
100;
ESAC;
IF ST(0) or SRC = QNaN, but not SNaN or unsupported format
Opcode
Instruction
Description
DD E0+i
FUCOM ST(i)
Compare ST(0) with ST(i)
DD E1
FUCOM
Compare ST(0) with ST(1)
DD E8+i
FUCOMP ST(i)
Compare ST(0) with ST(i) and pop register stack
DD E9
FUCOMP
Compare ST(0) with ST(1) and pop register stack
DA E9
FUCOMPP
Compare ST(0) with ST(1) and pop register stack twice
Comparison Results
C3
C2
C0
ST0 > ST(i)
0
0
0
ST0 < ST(i)
0
0
1
ST0 = ST(i)
1
0
0
Unordered
a
a. Flags not set if unmasked invalid-arithmetic- operand
(#IA) exception is generated.
1
1
1
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 ...