如何正确读取 MIPS 中的整数输入？
How do you properly read an integer input in MIPS?
以下程序
1. 打印出数组
2. 给定用户输入的下限和上限，确定该范围内的最小值和最小索引
它运行打印数组函数。
但是，我尝试跟踪 QTSPIM 中的寄存器，它没有正确地将下限和上限分别分配给 $a0 和 $a1。事实上，$v0 似乎甚至没有扫描任何东西。要将扫描的输入从 $v0 移动到 $t0，请尝试改用 "move $t0, $v0"。问题依旧。
# 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)
完整代码如下。如果有什么不对，谁能赐教？
# 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
您正确读入了整数。问题在别处
- 在
findMin 函数中您使用 lw, $t3, 0($a0)，但您应该将它与 $t0 一起使用而不是 $a0。
- 在你从这个函数 return 之后，你不小心将
$t1 保存为最小值，而不是实际保存它的 $t2。
- 此外，您没有保存保存最小值指针的
$v0，因此您稍后会使用一些垃圾数据，而不是预期的数据。
- 当你从你使用
add的指针计算最小值的索引时，但它应该是sub。
- 此外，正如
LoopEnd 的评论中提到的那样，add 在语法上是错误的。应该是addi $t0, $t0, 4。但这可能只是一些复制粘贴错误。
这是固定代码。已更改标有错误的行。
# 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
以下程序
1. 打印出数组
2. 给定用户输入的下限和上限，确定该范围内的最小值和最小索引
它运行打印数组函数。
但是，我尝试跟踪 QTSPIM 中的寄存器，它没有正确地将下限和上限分别分配给 $a0 和 $a1。事实上，$v0 似乎甚至没有扫描任何东西。要将扫描的输入从 $v0 移动到 $t0，请尝试改用 "move $t0, $v0"。问题依旧。
# 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)
完整代码如下。如果有什么不对，谁能赐教？
# 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
您正确读入了整数。问题在别处
- 在
findMin函数中您使用lw, $t3, 0($a0)，但您应该将它与$t0一起使用而不是$a0。 - 在你从这个函数 return 之后，你不小心将
$t1保存为最小值，而不是实际保存它的$t2。 - 此外，您没有保存保存最小值指针的
$v0，因此您稍后会使用一些垃圾数据，而不是预期的数据。 - 当你从你使用
add的指针计算最小值的索引时，但它应该是sub。 - 此外，正如
LoopEnd的评论中提到的那样，add 在语法上是错误的。应该是addi $t0, $t0, 4。但这可能只是一些复制粘贴错误。
这是固定代码。已更改标有错误的行。
# 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