MIPS input

Please enter MIPS code below to see the assembler output. A subset of MIPS is implemented. (Only guaranteed to work with the Ackermann function: Reset.) Comments should start with #. Or, view source code (now also on Github). See also: MIPhpS, the online MIPS simulator.

######################################################## # Ackermann's function implementation using MIPS assembly # C interface: # int AckermannFunc (int m,int n) ######################################################## .text .globl AckermannFunc # Preconditions: # 1st parameter ($a0) m # 2nd parameter ($a1) n # Postconditions: # result in ($v0) = value of A(m,n) # we are going to use $s0 as a temporary registers to store m sometimes AckermannFunc: # make space on stack addi $sp, $sp, -8 # preserve registers used by this function sw $s0, 4($sp) # preserve return address sw $ra, 0($sp) # move the parameter registers to temporary - no, only when nec. LABEL_IF: # check whether m==0 # if not then branch to LABEL_ELSE_IF bne $a0, $zero, LABEL_ELSE_IF # code for "result = n+1" addi $v0, $a1, 1 # jump to LABEL_DONE j LABEL_DONE LABEL_ELSE_IF: # check whether n==0 #if not then branch to LABEL_ELSE bne $a1, $zero, LABEL_ELSE # need to call A(m-1,1) # so initiate $a0,$a1 with m-1 and 1 addi $a0, $a0, -1 addi $a1, $zero, 1 # call AckermannFunc jal AckermannFunc # Return value already in $v0 # jump to LABEL_DONE j LABEL_DONE LABEL_ELSE: # This block may be a bit tricky ! ################################### # Save "m" to preserve it for the second ackermann call add $s0, $a0, $zero # call to acker(m, (n - 1)) addi $a1, $a1, -1 jal AckermannFunc # return value will be used very soon! # call to acker(m-1, acker(m, (n - 1))) # Take the "m" we saved and decrement it to be the new "m-1" :) addi $a0, $s0, -1 add $a1, $v0, $zero jal AckermannFunc # jump to LABEL_DONE j LABEL_DONE LABEL_DONE: # ALREADY loaded the return value register $v0 with result. # restore registers used by this function lw $s0, 4($sp) # restore return address lw $ra, 0($sp) # restore stack pointer addi $sp, $sp, 8 # return from this function jr $ra .text .globl Print # print: Print a message. # Preconditions: # 1st parameter (a0) m # 2nd parameter (a1) n # 3rd parameter (a2) value # Postconditions: # Prints the "Ackermann(m,n)=value" on the screen. Print: addi $sp, $sp, -4 # make space on stack sw $a0, 0($sp) # preserve first parameter m; la $a0, msg1 # load address of msg1 li $v0, 4 # load the "print string" syscall number syscall lw $a0, 0($sp) # load first parameter = m li $v0, 1 # load the "print integer" syscall number syscall la $a0, comma # load address of comma li $v0, 4 # load the "print string" syscall number syscall move $a0,$a1 # load second parameter = n li $v0, 1 # load the "print integer" syscall number syscall la $a0, msg2 # load address of msg2 li $v0, 4 # load the "print string" syscall number syscall move $a0, $a2 # load third parameter = value li $v0, 1 # load the "print integer" syscall number syscall la $a0, endl # load address of endl li $v0, 4 # load the "print string" syscall number syscall lw $a0, 0($sp) # restore first parameter addi $sp, $sp, 4 # restore stack pointer jr $ra # return .globl main # main: Test the towers function. main: addi $sp, $sp, -16 # make space on stack. sw $ra, 0($sp) # preserve return address. sw $s0, 4($sp) # preserve registers s0 through s2 sw $s1, 8($sp) # as we may clobber it in main sw $s2, 12($sp) la $a0, prompt_m # first parameter = prompt li $v0, 4 # load the "print string" syscall number syscall li $v0, 5 # load the "read integer" syscall number syscall move $s0, $v0 # m = s0 = value returned in v0 la $a0, prompt_n # second parameter = prompt li $v0, 4 # load the "print string" syscall number syscall li $v0, 5 # load the "read integer" syscall number syscall move $s1, $v0 # n = s1 = value returned in v0 # Ackermann parameter setup move $a0, $s0 # first parameter = m move $a1, $s1 # second parameter = n jal AckermannFunc move $s2, $v0 # Ackermann value = s2 = value returned # Print parameter setup move $a0, $s0 # first parameter = m move $a1, $s1 # second parameter = n move $a2, $s2 # jal Print li $v0, 0 # return value for main lw $ra, 0($sp) # restore return address lw $s0, 4($sp) # restore registers s0 through s3 lw $s1, 8($sp) # before exiting main lw $s2, 12($sp) addi $sp, $sp, 16 # restore stack pointer jr $ra # return to Operating System .data prompt_m: .asciiz "m=" prompt_n: .asciiz "n=" msg1: .asciiz "Ackermann(" msg2: .asciiz ")=" comma: .asciiz "," endl: .asciiz "\n"
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