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71 lines
1.5 KiB
71 lines
1.5 KiB
5 years ago
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# Simple routine to demo functions
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# NOT using a stack in this example.
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# Thus, the function does not preserve values
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# of calling function!
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# ------------------------------------------------------------------
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.text
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.globl main
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main:
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# Register assignments
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# $s0 = x
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# $s1 = y
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# Initialize registers
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lw $s0, x # Reg $s0 = x
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lw $s1, y # Reg $s1 = y
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# Call function
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move $a0, $s0 # Argument 1: x ($s0)
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jal fun # Save current PC in $ra, and jump to fun
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move $s1,$v0 # Return value saved in $v0. This is y ($s1)
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# Print msg1
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li $v0, 4 # print_string syscall code = 4
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la $a0, msg1
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syscall
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# Print result (y)
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li $v0,1 # print_int syscall code = 1
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move $a0, $s1 # Load integer to print in $a0
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syscall
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# Print newline
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li $v0,4 # print_string syscall code = 4
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la $a0, lf
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syscall
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# Exit
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li $v0,10 # exit
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syscall
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# ------------------------------------------------------------------
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# FUNCTION: int fun(int a)
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# Arguments are stored in $a0
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# Return value is stored in $v0
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# Return address is stored in $ra (put there by jal instruction)
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# Typical function operation is:
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fun: # Do the function math
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li $s0, 3
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mul $s1,$s0,$a0 # s1 = 3*$a0 (i.e. 3*a)
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addi $s1,$s1,5 # 3*a+5
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# Save the return value in $v0
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move $v0,$s1
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# Return from function
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jr $ra # Jump to addr stored in $ra
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# ------------------------------------------------------------------
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# Start .data segment (data!)
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.data
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x: .word 5
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y: .word 0
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msg1: .asciiz "y="
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lf: .asciiz "\n"
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