IPR-NIOS Altera, IPR-NIOS Datasheet - Page 282

• Manufacturer Part Number: IPR-NIOS
• Description: IP NIOS II MEGACORE RENEW
• Manufacturer: Altera
• Type: MegaCorer

Specifications of IPR-NIOS

• License: Renewal License
• Lead Free Status / RoHS Status: Not applicable / Not applicable

8–96
sub
Nios II Processor Reference Handbook
Operation:
Assembler Syntax:
Example:
Description:
Usage:
Exceptions:
Instruction Type:
Instruction Fields:
31
30
29
A
28
27
26
25
24
B
rC ← rA – rB
sub rC, rA, rB
sub r6, r7, r8
Subtract rB from rA and store the result in rC.
Carry Detection (unsigned operands):
The carry bit indicates an unsigned overflow. Before or after a sub operation, a carry out of
the MSB can be detected by checking whether the first operand is less than the second
operand. The carry bit can be written to a register, or a conditional branch can be taken based
on the carry condition. Both cases are shown below.
sub rC, rA, rB
cmpltu rD, rA, rB
sub rC, rA, rB
bltu rA, rB, label
Overflow Detection (signed operands):
Detect overflow of signed subtraction by comparing the sign of the difference that is written
to rC with the signs of the operands. If rA and rB have different signs, and the sign of rC is
different than the sign of rA, an overflow occurred. The overflow condition can control a
conditional branch, as shown below.
sub rC, rA, rB
xor rD, rA, rB
xor rE, rA, rC
and rD, rD, rE
blt rD, r0, label
None
R
A = Register index of operand rA
B = Register index of operand rB
C = Register index of operand rC
23
22
21
20
19
C
18
17
16
# The original sub operation (optional)
# rD is written with the carry bit
# The original sub operation (optional)
# Branch if carry generated
# The original sub operation
# Compare signs of rA and rB
# Compare signs of rA and rC
# Combine comparisons
# Branch if overflow occurred
15
14
0x39
13
12
11
10
9
0
8
Chapter 8: Instruction Set Reference
December 2010 Altera Corporation
7
6
5
Instruction Set Reference
4
0x3a
3
subtract
2
1
0