(20 pts) Exercise 2-28
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(10 pts) Add comments to the MIPS code above. This code processes two arrays and
produces an important value in register $v0. Assume that each array consists of 2500
words indexed 0 through 2499, that the base addresses of the arrays are stored in $a0 and
$a1 respectively, and their sizes (2500) and stored in $a2 and $a3, respectively. In your
comments, call the arrays Array1 and Array2.
(10 pts) In one sentence, what does this code compute and store in $v0? Be very specific
(make sure that your answer doesn’t have more than one interpretation of what it means)
The code determines the total number of matching elements between the two
arrays (in any position) and returns this number in register $v0.
Another way of saying this is as follows:
Let ci = the number of times that array1[i] appears at any position in array2.
Then this program computes c0 + c1 + … + c2499.
(5 pts) Exercise 2-31
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Suppose you are given the code for the following function:
int function1(int a, int b);
Write MIPS code to call function1(3, 7) and then store the result in $s0
addi $a0, $zero, 3
addi $a1, $zero, 7
jal function1
move $s0, $v0
(5 pts) Exercise 2-32
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Now you have this definition for function1:
int function1(int a, int b) {
return (a – b);
}
Write MIPS code to define function1.
function1:
sub $v0, $a0, $a1
jr $ra
(10 pts) Exercise 2-33
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Write MIPS code to define the following function:
int cat(int a, int b) {
cat:
if (a < b)
blt $a0, $a1, DoA # skip ahead if a<b
return a;
move $vo, $a1
# if not, retval = b
else
j Exit
return b;
DoA:
}
move $v0, $a0
# retval = a
Exit:
jr $ra
# actually return
(5 pts) Exercise 2-36
Save $ra b/c nested
Save $a0 because need ‘a’ after sub-call
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Write the MIPS code to define the following function
int function2(int g, int h)
{ return g + function1(g, h); }
(You will need to store something on the stack – why?)
function2:
addi $sp, $sp, -8
sw $ra, 4($sp)
sw $a0, 0($sp)
jal function1
lw $ra, 4($sp)
lw $a0, 0($sp)
addi $sp, $sp, 8
add $v0, $v0, $a0
jr $ra
A VITAL exercise to understand for the project.
(5 pts)
MustExercise
store results of2-37
function6(a) and param b (saving param ‘a’ is optional)
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Soln A:We use $s0 to store result of function6 –so must save/restore $s0!
Solnthe
B: Store
the stackfunction
Write
MIPS result
code of
to function6
define theon
following
int function3(int a, int b)
{ return function6(a) + function7(b); }
(You will need to store something on the stack – why?)
function3:
# Solution A
addi $sp, $sp, -16
sw $ra, 0($sp)
sw $a0, 4($sp)
sw $a1, 8($sp)
sw $s0, 12($sp) # we modify, so must save!
jal function6 # args in right place already
move $s0, $v0 # save for later
function3:
addi $sp, $sp, -16
sw $ra, 0($sp)
sw $a0, 4($sp)
sw $a1, 8($sp)
# Solution B
jal function6 # args in right place already
sw $v0, 12($sp) # save for later
lw $a0, 8($sp) # get b
jal function7
add $v0, $v0, $s0 # add two results
lw $a0, 8($sp) # get b
jal function7
lw $t0, 12($sp)
# get function6 result back
add $v0, $v0, $t0 # add two results
lw $ra, 0($sp)
lw $s0, 12($sp) # must restore
addi $sp, $sp, 16
jr $ra
lw $ra, 0($sp)
addi $sp, $sp, 16
jr $ra
(15 pts) Exercise 2-38
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Write the MIPS code to define the following function
int lemur(int a, int b)
lemur:
{ return panda(a) + b; }
addi $sp, $sp, -8
sw $ra, 4($sp)
sw $a1, 0($sp) # save ‘b’ for later
# ‘a’ already in $a0, so call panda now
jal panda
# result now in $v0
# warning -- $a0, $a1, others now clobbered!
# reload stored values and fix up stack
lw $ra, 0($sp)
lw $a1, 4($sp)
# reload b (was clobbered)
addi $sp, $sp, 8
# add panda result to ‘b’, put in $v0
add $v0, $v0, $a1
jr $ra
(15 pts) Exercise 2-39
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Write the MIPS code to define the following
alpaca: function
int alpaca(int x, int y, int z)
addi $sp, $sp, -8
function2:
sw
$ra, 4($sp)
{ int temp = ferret(y, z);
$sp, -8# save ‘x’ for later
swaddi
$a1,$sp,
0($sp)
return hedgehog(temp + x);
sw $ra, 4($sp)
}
sw $a0,
$a1, $a1
0($sp)# set
# save
later
move
first ‘b’
argfor
to ‘y’
move $a1, $a2 # set second arg to ‘z’
‘a’ already in $a0,
so call
jal#ferret
# result
nowpanda
in $v0now
(temp)
jal panda
# result now in $v0
lw $a0, 4($sp)
# reload x
# reload
stored
fix up (get
stacktemp
add
$a0, $a0,
$v0values
# addand
in ‘temp’
$ra, 0($sp) # call hedgehog(temp+x)
jallw
hedgehog
lw $a1, 4($sp)
# reload b
addi $sp,
$sp,values
8
# reload
stored
and fix up stack
lw $ra, 0($sp)
# add
addi
$sp,panda
$sp, 8result to ‘b’, put in $v0
add $v0, $v0, $a1
$ra
jr jr
$ra