1. Conditional Branches
What distinguishes a computer from a simple calculator is its ability to make decisions
Decisions are made using the if statement, sometimes combined with “go to” statements and “labels”.
MIPS assembly language includes many decision-making instructions. Two of them are BEQ and BNE.

2. Branch on Equal if ($u == $v) then jump to “Label” beq u,v,Label
if the bit patterns in register $u == register $v
PC <-- address of Label
after a delay of one machine cycle.
else
Continue the sequence of instructions without jumping.
bit patterns – unsigned or two’s complement ?

3. “If” structure IF $8 equals to $9 then go to CONT.
Otherwise do the block of statements
Then again go through the CONT

4. “If” structure on assembly
The bit patterns in two registers are compared.
If the bit patterns are the same, the PC is changed to the branch address.
There is a branch delay following the instruction (just as for a jump instruction).
# load values into $8 and $9
beq $8,$9,cont # branch if equal sll $0,$0, # branch delay slot
# conditionally
# executed
# statements
cont: add $10,$10,$11 # always executed

5. ? Two – way decision ... # load values into # $8 and $9
beq $8,$9,equal # branch if equal
sll $0,$0, # branch delay slot #
# false branch
j cont
equal: #
# true branch
cont: add $10,$10,$11 # always executed ?

6. Branch on Not Equal if ($u != $v) then jump to “Label” bne u, v, Label
if register $u != register $v
PC <-- address of Label
after a delay of one machine cycle.
else
Continue the sequence of instructions without jumping.

7. Absolute Value calculation
# Get A
lui $10,0x # base register
lw $8,0($10) # Load A
sll $0,$0, # no-op
# Is A Negative?
srl $9,$8, # Shift sign bit
beq $0,$9,done # sign bit == zero
# Store –A
sub $8,$0,$8 # negate A
sw $8,0($10) # save it
done: sll $0,$0, # target of the branch
.data
A: .word -1

8. BEQ instruction format
beq $0, $9, done
beq $0 $
opcode oprnd dest offset(2’s comp.)
New PC = PC + Off*4
= 0x x0003*4
= 0x x C
= 0x
[0x ] 0x3c0a1000 lui $10, 4096
[0x ] 0x8d lw $8, 0($10)
[0x ] 0x nop
[0x c] 0x00084fc2 srl $9, $8, 31
PC+4 [0x ] 0x beq $0,$9,12 [done-0x ]
[0x ] 0x nop
+12 [0x ] 0x sub $8, $0, $8
[0x c] 0xad sw $8, 0($10)
done:[0x ] 0x nop

9. Addressing Modes
4. BEQ and BNE use PC-relative addressing, where the branch address is the sum of the PC and a
constant in the instruction
Addressing mode – One of several addressing regimes delimited by their varied use of operands and or addresses.