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362
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 3:
User Programming Model
R
CR1 Field
In PowerPC
®
implementations that support floating-point operations, the CR1 field can be
updated by the processor to reflect the result of those operations. Because the PPC405 does
not support floating-point operations in hardware, CR1 is not updated in this manner.
CR
n
Fields (Compare Instructions)
Any one of the eight CR
n
fields (including CR0 and CR1) can be updated to reflect the
result of a compare instruction. The CR
n
-field bits are interpreted as described in
Table 3-1:
CR0-Field Bit Settings
Bit
Name
Function
Description
0
LT
Negative
0—Result is not negative.
1—Result is negative.
This bit is set when the result is negative, otherwise it is cleared.
1
GT
Positive
0—Result is not positive.
1—Result is positive.
This bit is set when the result is positive (and not zero), otherwise
it is cleared.
2
EQ
Zero
0—Result is not equal to zero.
1—Result is equal to zero.
This bit is set when the result is zero, otherwise it is cleared.
3
SO
Summary overflow
0—No overflow occurred.
1—Overflow occurred.
This is a copy of the final state of XER[SO] at the completion of the
instruction.
Table 3-2:
CR
n
-Field Bit Settings
Bit
Name
Function
Description
0
LT
Less than
0—
r
A is not less than.
1—
r
A is less than.
This bit is set when
r
A
<
SIMM or
r
B (signed comparison), or
r
A
<
UIMM or
r
B (unsigned comparison),
otherwise it is cleared.
1
GT
Greater than
0—
r
A is not greater than.
1—
r
A is greater than.
This bit is set when
r
A
>
SIMM or
r
B (signed comparison), or
r
A
>
UIMM or
r
B (unsigned comparison),
otherwise it is cleared.
2
EQ
Equal to
0—
r
A is not equal.
1—
r
A is equal.
This bit is set when
r
A
=
SIMM or
r
B (signed comparison), or
r
A
=
UIMM or
r
B (unsigned comparison),
otherwise it is cleared.
3
SO
Summary overflow
0—No overflow occurred.
1—Overflow occurred.
This is a copy of the final state of XER[SO] at the completion of the
instruction.
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