Assembler Directives Example program: .data # DATA segment city: .asciiz “Seattle” .align 2 num: .word 2210, 2341, 26, 0x022ec, 0x11110087 .byte 65, 79, 253 .text # CODE segment .globl main # declaring “main” as global main: li $v0, 4 # syscall for print_string la $a0, city # argument in $a0 syscall la $t0, num # get address of first number lw $s0, 0($t0) # s0 = 2210 lw $s1, 4($t0) # s1 = 2341 add $s0, $s0, $s1 # s0 = 2210+2341 li $v0, 1 # syscall for print_int move $a0, $s0 # argument in $a0 syscall .end main

General format of MIPS programs Xspim on our machines automatically loads some assembly code that takes care of calling “main” Need to write code that looks roughly like the following: .data # DATA segment lab1: .byte ……… lab2: .asciiz …… # some static data .float ……… lab3: .double ……... .text # CODE segment .globl main # declaring “main” as global main: <your part of the code> … ... .end main

If-then-else in MIPS What does the following C code looks like in MIPS assembly language: if (a < b) { a = a + 1; b = b - 1; } else { a = a * 2; b = b / 2; } Assume $s0 contains a, and $s1 contains b.

If-then-else (cont.) # if (a < b) slt $t0, $s0, $s1 beq $t0, $zero, else_label # a = a + 1, b = b - 1 addi $s0, $s0, 1 subi $s1, $s1, 1 j end_label # else a = a * 2, b = b / 2 else_label: sll $s0, $s0, 1 sra $s1, $s1, 1 # end of if-then-else end: <statements following if-then-else>

From C Program to Machine Language Stages in the transformation: C program Compiler Assembly Language program Assembler Object : Machine Language Module Library routines Machine Lang Linker Executable (Machine Language) Loader Memory