Add Immediate - Altera Nios II User Manual

8–8
addi
Operation:
Assembler Syntax:
Example:
Description:
Usage:
Exceptions:
Instruction Type:
Instruction Fields:
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A
Nios II Processor Reference Handbook
rB ← rA + σ (IMM16)
addi rB, rA, IMM16
addi r6, r7, -100
Sign-extends the 16-bit immediate value and adds it to the value of rA. Stores the sum in rB.
Carry Detection (unsigned operands):
Following an addi operation, a carry out of the MSB can be detected by checking whether the
unsigned sum is less than one of the unsigned operands. The carry bit can be written to a
register, or a conditional branch can be taken based on the carry condition. The following code
shows both cases:
addi rB, rA, IMM16
cmpltu rD, rB, rA
addi rB, rA, IMM16
bltu rB, rA, label
Overflow Detection (signed operands):
An overflow is detected when two positives are added and the sum is negative, or when two
negatives are added and the sum is positive. The overflow condition can control a conditional
branch, as shown in the following code:
addi rB, rA, IMM16
xor rC, rB, rA
xorhi rD, rB, IMM16
and rC, rC, rD
blt rC, r0,label
None
I
A = Register index of operand rA
B = Register index of operand rB
IMM16 = 16-bit signed immediate value
24 23 22 21 20 19 18 17
B
# The original add operation
# rD is written with the carry bit
# The original add operation
# Branch if carry generated
# The original add operation
# Compare signs of sum and rA
# Compare signs of sum and IMM16
# Combine comparisons
# Branch if overflow occurred
16 15 14 13 12 11 10 9
IMM16
Chapter 8: Instruction Set Reference
Instruction Set Reference

add immediate

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February 2014 Altera Corporation
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