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746
March 2002 Release
1-800-255-7778
Virtex-II Pro™ Platform FPGA Documentation
Chapter 11:
Instruction Set
R
subfme
Subtract from Minus One Extended
Description
The value -1 is added to the one’s complement of register
r
A. The contents of XER[CA] are
added to the result. The result is loaded into register
r
D.
XER[CA] is updated to reflect the unsigned magnitude of the result.
The subtract-from extended instructions can be used to perform subtraction on integers
larger than 32 bits, as described on
.
Pseudocode
(
r
D)
← ¬
(
r
A) + 0xFFF XER[CA]
if
(
r
D)
2
32
−
1
then XER[CA]
←
1
else
XER[CA]
←
0
Registers Altered
•
r
D.
•
XER[CA].
•
CR[CR0]
LT, GT, EQ, SO
if Rc
=
1.
•
XER[SO, OV] if OE
=
1.
Exceptions
Execution of any of the following invalid-instruction forms results in a boundedly-
undefined result rather than a program exception:
•
Reserved bits containing a non-zero value.
Compatibility
This instruction is defined by the PowerPC user instruction-set architecture (UISA). It is
implemented by all PowerPC processors.
subfme
r
D,
r
A
(OE=0, Rc=0)
subfme.
r
D,
r
A
(OE=0, Rc=1)
subfmeo
r
D,
r
A
(OE=1, Rc=0)
subfmeo.
r
D,
r
A
(OE=1, Rc=1)
XO Instruction Form
31
r
D
r
A
0
0
0
0
0
OE
232
Rc
0
6
1
1
1
6
2
1
2
2
3
1
>
u
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