# 3827 Homework 3, problem 2, "eval" # # , # # Invoke with, e.g., spim -file eval.s # .text # $a0 : pointer to an expression eval: # Your solution here li $v0, 0 jr $ra ###################################################################### # # Test harness: extend to add tests # .data # Expression nodes take three forms: # .word 0, 1 # Leaf: value # .word '!', e10 # Unary negation operator # .word '+', e42, e17 # Binary operator: +, left is e42, right is e17 e1: .word 0, 1 e0: .word 0, 0 e4: .word 0, 4 eadd: .word '+', e0, e4 eadd2: .word '+', e0, e1 eadd3: .word '+', e1, e1 eadd4: .word '+', e1, e4 e2: .word 0, 2 e3: .word 0, 3 eadd5: .word '+', e2, e3 eadd6: .word '+', eadd4, eadd2 e5: .word 0, 7 emult1: .word '*', e5, eadd3 exor1: .word '^', e0, e0 exor2: .word '^', e0, e1 exor3: .word '^', e1, e1 exor4: .word '^', eadd, eadd4 eneg1: .word '!', e3 eneg2: .word '!', exor4 # Add more test expressions here nl: .asciiz "\n" lparen: .asciiz "(" onechar: .asciiz " " rparen: .asciiz ")" equals: .asciiz " = " .text # Print an expression tree # $a0 : address of the root of the expression tree print: lb $t0, 0($a0) bne $t0, $0, prbranch lw $a0, 4($a0) # leaf: print its value li $v0, 1 syscall jr $ra prbranch: addiu $sp, $sp, -8 # Save $ra and $s0 on the stack sw $ra, 0($sp) sw $s0, 4($sp) move $s0, $a0 # Remember the tree node bne $t0, '!', .L1 la $a0, onechar sb $t0, 0($a0) li $v0, 4 syscall la $a0, lparen # print ( li $v0, 4 syscall lw $a0, 4($s0) # print(left) jal print b .L2 .L1: la $a0, lparen # print ( li $v0, 4 syscall lw $a0, 4($s0) # print(left) jal print lb $t0, 0($s0) # print(op) la $a0, onechar sb $t0, 0($a0) li $v0, 4 syscall lw $a0, 8($s0) # print(right) jal print .L2: la $a0, rparen # print ) li $v0, 4 syscall lw $ra, 0($sp) # Restore $ra and $s0 lw $s0, 4($sp) addiu $sp, $sp, 8 jr $ra # Print an expression tree, evaluate it, and print the result # $a0 : address of the root of the expression tree preval: addiu $sp, $sp, -8 # Save $ra and $s0 sw $ra, 0($sp) sw $s0, 4($sp) move $s0, $a0 jal print # Print the expression la $a0, equals # Print " = " li $v0, 4 syscall move $a0, $s0 # Call eval on the expression jal eval move $a0, $v0 # Print the (integer) result li $v0, 1 syscall la $a0, nl # Print a newline li $v0, 4 syscall lw $ra, 0($sp) # Restore $ra and $s0 lw $s0, 4($sp) addiu $sp, $sp, 8 jr $ra .globl main # Run a number of tests main: move $s0, $ra la $a0, e1 # preval(e1) jal preval la $a0, e0 jal preval la $a0, e4 jal preval la $a0, eadd jal preval la $a0, eadd2 jal preval la $a0, eadd3 jal preval la $a0, eadd4 jal preval la $a0, emult1 jal preval la $a0, eadd5 jal preval la $a0, eadd6 jal preval la $a0, eneg1 jal preval la $a0, exor1 jal preval la $a0, exor2 jal preval la $a0, exor3 jal preval la $a0, exor4 jal preval la $a0, eneg2 jal preval # Add your own tests here move $ra, $s0 jr $ra