The following program
1. Prints out the array
2. Given a lower and upper bound input by user, determines the min and min index within that range
It runs the print array function.
However, I tried tracing the registers in QTSPIM, it does not correctly assign the lower bound and upper bound to $a0 and $a1 respectively. In fact, $v0 does not seem to even scan anything. To move the scanned input from $v0 to $t0, tried using "move $t0, $v0" instead. The problem still occurs.
# Ask the user for two indices
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (lower bound)
add $a0, $t9, $t0 # array pointer (lower bound)
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (upper bound)
add $a1, $t9, $t0 # array pointer (upper bound)
The full code is below. Can anyone enlighten me if there's anything wrong?
# arrayFunction.asm
.data
array: .word 8, 2, 1, 6, 9, 7, 3, 5, 0, 4
newl: .asciiz "\n"
.text
main:
# Print the original content of array
# setup the parameter(s)
la $a0, array # base address of array
add $t9, $a0, $zero # store base address
la $a1, 10 # number of elements in array
# call the printArray function
jal printArray # call function
# Ask the user for two indices
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (lower bound)
add $a0, $t9, $t0 # array pointer (lower bound)
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (upper bound)
add $a1, $t9, $t0 # array pointer (upper bound)
# Call the findMin function
# setup the parameter(s)
# call the function
jal findMin # call function
# Print the min item
# place the min item in $t3 for printing
addi $t3, $t1, 0
# Print an integer followed by a newline
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # print $t3
syscall # make system call
li $v0, 4 # system call code for print_string
la $a0, newl
syscall # print newline
#Calculate and print the index of min item
la $a0, array
add $t3, $v0, $a0
srl $t3, $t3, 2
# Place the min index in $t3 for printing
# Print the min index
# Print an integer followed by a newline
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # print $t3
syscall # make system call
li $v0, 4 # system call code for print_string
la $a0, newl #
syscall # print newline
# End of main, make a syscall to "exit"
li $v0, 10 # system call code for exit
syscall # terminate program
#######################################################################
### Function printArray ###
#Input: Array Address in $a0, Number of elements in $a1
#Output: None
#Purpose: Print array elements
#Registers used: $t0, $t1, $t2, $t3
#Assumption: Array element is word size (4-byte)
printArray:
addi $t1, $a0, 0 #$t1 is the pointer to the item
sll $t2, $a1, 2 #$t2 is the offset beyond the last item
add $t2, $a0, $t2 #$t2 is pointing beyond the last item
l1:
beq $t1, $t2, e1
lw $t3, 0($t1) #$t3 is the current item
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # integer to print
syscall # print it
addi $t1, $t1, 4
j l1 # Another iteration
e1:
li $v0, 4 # system call code for print_string
la $a0, newl #
syscall # print newline
jr $ra # return from this function
#######################################################################
### Student Function findMin ###
#Input: Lower Array Pointer in $a0, Higher Array Pointer in $a1
#Output: $v0 contains the address of min item
#Purpose: Find and return the minimum item
# between $a0 and $a1 (inclusive)
#Registers used: $t0 (counter), $t1 (max add), $t2 (min), $v0 (min pos), $t3 (current item)
#Assumption: Array element is word size (4-byte), $a0 <= $a1
findMin:
lw, $t2, 0($a0) # initialise min (value) to the lower bound
addi $t0, $a0, 0 # initialise $t0 (current pointer) to lower bound
addi $t1, $a1, 0 # initialise $t1 (add of end of array) to upper bound
Loop: slt $t4, $t1, $t0
bne $t4, $zero, End # branch to end if upper < lower
lw, $t3, 0($a0) # store the content of the lower array pointer
slt $t4, $t3, $t2 # if current ($t3) < min ($t2), store 1 in $t4
beq $t4, $zero, LoopEnd # if it is 0, go to LoopEnd
addi $t2, $t3, 0 # store content ($t3) as minimum ($t2)
addi $v0, $t0, 0 # store the address of min
LoopEnd: addi, $t0, 4 # increments current pointer lower bound
j Loop # Jump to loop
End:
jr $ra # return from this function
You read in the integers properly. The problems are elsewhere
findMin function you use lw, $t3, 0($a0), but you should use it with $t0 instead of $a0.$t1 as min value rather then $t2 which actually holds it.$v0 which holds the pointer for the min value, so you use some garbage data later on, not the intended one. add, but it should be sub.LoopEnd the add is syntactically wrong. It should be addi $t0, $t0, 4. But this maybe just some copy paste error.Here is the fixed code. Changed lined marked with ERROR.
# arrayFunction.asm
.data
array: .word 8, 2, 1, 6, 9, 7, 3, 5, 0, 4
newl: .asciiz "\n"
.text
main:
# Print the original content of array
# setup the parameter(s)
la $a0, array # base address of array
add $t9, $a0, $zero # store base address
la $a1, 10 # number of elements in array
# call the printArray function
jal printArray # call function
# Ask the user for two indices
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (lower bound)
add $a0, $t9, $t0 # array pointer (lower bound)
li $v0, 5 # System call code for read_int
syscall
add $t0, $v0, $zero # store input in $t0
sll $t0, $t0, 2 # relative address position (upper bound)
add $a1, $t9, $t0 # array pointer (upper bound)
# Call the findMin function
# setup the parameter(s)
# call the function
jal findMin # call function
# Print the min item
# place the min item in $t3 for printing
addi $t3, $t2, 0 # ERROR: min is in $t2 not $t1
addi $t4, $v0, 0 # ERROR: not saving the pointer to the min element
# Print an integer followed by a newline
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # print $t3
syscall # make system call
li $v0, 4 # system call code for print_string
la $a0, newl
syscall # print newline
#Calculate and print the index of min item
la $a0, array
sub $t3, $t4, $a0 # ERROR: sub should used not add
srl $t3, $t3, 2
# Place the min index in $t3 for printing
# Print the min index
# Print an integer followed by a newline
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # print $t3
syscall # make system call
li $v0, 4 # system call code for print_string
la $a0, newl #
syscall # print newline
# End of main, make a syscall to "exit"
li $v0, 10 # system call code for exit
syscall # terminate program
#######################################################################
### Function printArray ###
#Input: Array Address in $a0, Number of elements in $a1
#Output: None
#Purpose: Print array elements
#Registers used: $t0, $t1, $t2, $t3
#Assumption: Array element is word size (4-byte)
printArray:
addi $t1, $a0, 0 #$t1 is the pointer to the item
sll $t2, $a1, 2 #$t2 is the offset beyond the last item
add $t2, $a0, $t2 #$t2 is pointing beyond the last item
l1:
beq $t1, $t2, e1
lw $t3, 0($t1) #$t3 is the current item
li $v0, 1 # system call code for print_int
addi $a0, $t3, 0 # integer to print
syscall # print it
addi $t1, $t1, 4
j l1 # Another iteration
e1:
li $v0, 4 # system call code for print_string
la $a0, newl #
syscall # print newline
jr $ra # return from this function
#######################################################################
### Student Function findMin ###
#Input: Lower Array Pointer in $a0, Higher Array Pointer in $a1
#Output: $v0 contains the address of min item
#Purpose: Find and return the minimum item
# between $a0 and $a1 (inclusive)
#Registers used: $t0 (counter), $t1 (max add), $t2 (min), $v0 (min pos), $t3 (current item)
#Assumption: Array element is word size (4-byte), $a0 <= $a1
findMin:
lw, $t2, 0($a0) # initialise min (value) to the lower bound
addi $t0, $a0, 0 # initialise $t0 (current pointer) to lower bound
addi $t1, $a1, 0 # initialise $t1 (add of end of array) to upper bound
Loop:
slt $t4, $t1, $t0
bne $t4, $zero, End # branch to end if upper < lower
lw, $t3, 0($t0) # store the content of the lower array pointer, ERROR: t0 should be used not a0
slt $t4, $t3, $t2 # if current ($t3) < min ($t2), store 1 in $t4
beq $t4, $zero, LoopEnd # if it is 0, go to LoopEnd
addi $t2, $t3, 0 # store content ($t3) as minimum ($t2)
addi $v0, $t0, 0 # store the address of min
LoopEnd:
addi $t0, $t0, 4 # increments current pointer lower bound
j Loop # Jump to loop
End:
jr $ra # return from this function