1. The University of Adelaide, School of Computer Science
17 January 2019
Lecture 2
Instructions:
Logical Operations
Chapter 2 — Instructions: Language of the Computer

2. Objectives
Perform left/right shift operations on the contents of registers
Perform bitwise operations on contents
Perform zero extension on 16-bit immediate values
Chapter 2 — Instructions: Language of the Computer — 2

3. Coverage Textbook Chapter 2.6
Chapter 2 — Instructions: Language of the Computer — 3

4. The University of Adelaide, School of Computer Science
17 January 2019
Logical Operations
Instructions for bitwise manipulation
§2.6 Logical Operations
Operation C
Java
MIPS
Shift left
<<
sll
Shift right
>>
>>>
srl
Bitwise AND
&
and, andi
Bitwise OR |
or, ori
Bitwise NOT ~
nor
Useful for extracting and inserting groups of bits in a word
Chapter 2 — Instructions: Language of the Computer — 4
Chapter 2 — Instructions: Language of the Computer

5. The University of Adelaide, School of Computer Science
17 January 2019
Shift Operations - sll op rs rt rd
shamt
funct
6 bits
5 bits
shamt: how many positions to shift
Shift left logical
Shift left and fill with 0 bits
sll by i bits: multiplies by 2i
sll $rd, $rt, shamt # R[rd]=R[rt]<<shamt
sll $t0, $t0, 4 8 4
6 bits
5 bits
Chapter 2 — Instructions: Language of the Computer — 5
Chapter 2 — Instructions: Language of the Computer

6. The University of Adelaide, School of Computer Science
17 January 2019
Shift Operations - srl op rs rt rd
shamt
funct
6 bits
5 bits
shamt: how many positions to shift
Shift right logical
Shift right and fill with 0 bits
srl by i bits: divides by 2i
For non-negative number only
srl $rd, $rt, shamt # R[rd]=R[rt]>>shamt
srl $s0, $t0, 4 8 16 4 2
6 bits
5 bits
Chapter 2 — Instructions: Language of the Computer — 6
Chapter 2 — Instructions: Language of the Computer

7. Bitwise Operations Bitwise logical operations in MIPS ISA
and $rd, $rs, $rt # R[rd] = R[rs] & R[rt]
or $rd, $rs, $rt # R[rd] = R[rs] | R[rt]
nor $rd, $rs, $rt # R[rd] = ~ (R[rs] | R[rt])
Instruction Format (R format) op rs rt rd
shamt
funct
6 bits
5 bits
nor $t0, $t1, $t2 9 10 8
0x24
Chapter 2 — Instructions: Language of the Computer — 7

8. The University of Adelaide, School of Computer Science
17 January 2019
AND Operations
Useful to mask bits in a word
Select some bits, clear others to 0
and $t0, $t1, $t2
$t2
$t1
$t0
Chapter 2 — Instructions: Language of the Computer — 8
Chapter 2 — Instructions: Language of the Computer

9. The University of Adelaide, School of Computer Science
17 January 2019
OR Operations
Useful to set bits in a word
Set some bits to 1, leave others unchanged
or $t0, $t1, $t2
$t2
$t1
$t0
Chapter 2 — Instructions: Language of the Computer — 9
Chapter 2 — Instructions: Language of the Computer

10. The University of Adelaide, School of Computer Science
17 January 2019
NOT Operations
Useful to invert bits in a word
Change 0 to 1, and 1 to 0
MIPS does not have NOT instruction
MIPS has NOR 3-operand instruction
a NOR b == NOT ( a OR b )
nor $t0, $t1, $zero
Register 0: always read as zero
$t1
$t0
Chapter 2 — Instructions: Language of the Computer — 10
Chapter 2 — Instructions: Language of the Computer

11. Logical Operations with Immediate
Bitwise logical operations with immediate
andi $rt, $rs, Imm # R[rt] = R[rs] & ZeroExtImm
ori $rt, $rs, Imm # R[rt] = R[rs] | ZeroExtImm
Instruction Format (I format) op rs rt
Immediate
6 bits
5 bits
16 bits
andi $t0, $t1, 0xFF00
0x0C 9 8
0xFF00
6 bits
5 bits
16 bits
Chapter 2 — Instructions: Language of the Computer — 11