1
CS240 Computer Organization
Department of Computer Science
Wellesley College
Decisions
Shifting and branching
Programmer’s cheer
Shift to the left
Shift to the right
Pop up
Push down
Byte, byte, byte
3-2 Decisions
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MIPS Instruction Set: Decisions and Logical Operations, Study notes of Computer Science
An overview of various decisions and logical operations in the mips instruction set. Topics include shifting and branching, logical operations such as and, or, and not, and data transfer instructions. The document also discusses the use of constant values and the lack of a not operation, as well as conditional branches and compiling if-then-else and while loops.
Typology: Study notes
Pre 2010
1 / 6
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CS240 Computer Organization
Department of Computer Science
Wellesley College
Decisions
Shifting and branching
Programmer’s cheer
Shift to the left
Shift to the right
Pop up
Push down
Byte, byte, byte
Decisions 3-
Logical operations
add add $s1,$s2,$s3 $s1=$s2 + $s
Arithmetic subtract sub $s1,$s2,$s3 $s1=$s2 - $s
add immediate addi $s1,$s2,100 $s1=$s2 + 100
and and $s1,$s2,$s3 $s1=$s2 & $ s
or or $s1,$s2,$s3 $s1=$s2 | $s
nor nor $s1,$s2,$s3 $s1=~($s2 | $s3)
Logical and immediate andi $s1,$s2,100 $s1=$s2 & 100
or immediate ori $s1,$s2,100 $s1=$s2 | 100
sll sll $s1,$s2,10 $s1=$s2 << 10
srl srl $s1,$s2,10 $s1=$s2 >> 10
Data transfer load word lw $s1,100($s2) $s1=Mem[$s2+100]
store word sw $s1, 100($s2) Mem[$s2+100]=$s
Decisions 3-
sll $t2, $s0, 4
op rs rt rd shamt funct
000000 00000 10000 01010 00100 00000
6 bits 5 bits 5 bits 5 bits 5 bits 6 bits
*R-type (for register) or R-format.
Decisions 3-
Alas, no NOT
o In keeping with the two-operand format, the
designers of MIPS decided against a NOT
operation.
o A NOR operation is offered in consolation.*
nor $t0, $t1, $t2 # $t0 = ~($t1 | $t3)
*How does this help?
Decisions 3-
Conditional branches
o MIPS includes two decision-making instructions
similar to the infamous “if with goto”.
o Branch if equal:
beq register1, register2, label
o Branch if not equal:
beq register1, register2, label
Decisions 3-
Compiling if-then-else clauses
o Let’s try an easy one
if (i == j)
f = g + h;
else
f = g - h;
o We assume variable f to j
correspond to registers
$s0 to $s4.
i==j?
i=j
i≠j
Else:
f=g-h f=g+h
Exit:
Decisions 3-
Compiling while loops
o One only slightly harder
while (save[i] == k)
i += 1;
o We assume that i and k
correspond to registers
$s3 and $r5 and the base
address of save is in $s6.
$t1==k?
$t1=k
$t1≠k
i+=
Exit:
calc addr
of save[i]
ld to $t
Loop:
Decisions 3-