Main.s

@ Main.s
@ This program generates a random number between 1 and 6 twice and adds them together.
 @ It does this 1000 times and keeps track of how many times each sum (2-12) is rolled 
 @ using an array. It then prints the empirical distribution of each sum rolled.

.cpu cortex-a53
.fpu neon-fp-armv8

.data

.text
.align 2
.global main
.syntax unified
.type main, %function

main:
	push	{fp, lr}		@ Pushes fp and lr onto the stack
   	add 	fp, sp, #4		@ Adds 4 to sp and stores it in fp

	mov	r0, #13			@ Moves the size of the array + 2 (13) into r0
	mov	r0, r0, LSL #2		@ Multiplies r0 by 4 and moves that into r0
					 @ This is the amount of memory needed
	sub	sp, sp, r0		@ Moves the stack pointer to point to the start of the array
	str	sp, [fp, #-8]		@ Stores the stack pointer address into the first available memory address	
	mov	r0, #11			@ Moves #11 into r0
	str	r0, [fp, #-12]		@ Stores array size into second available memory address	
	ldr	r1, [fp, #-12]		@ Loads size of array into r1
	ldr	r0, [fp, #-8]		@ Loads the address of the first array index into r0

	bl	initArray		@ Branches to initArray function

	mov	r9, #0			@ Moves #0 into r9. This is the counter for our primary loop
	mov	r0, #0			@ Moves 0 into r0 for the time and srand calls
	bl	time			@ Gets time from clock
	bl	srand			@ Sets seed for srand

loop1:
	cmp	r9, #1000		@ Compares r9 with 1000
	bge	outloop1		@ If it is greater than or equal to 1000, exit loop
	
	bl 	rollDie			@ Branches to rollDie function
	mov	r4, r0			@ Moves number returned by rollDie into r4
	bl	rollDie			@ Branches to rollDie function
	add	r4, r4, r0		@ Adds the number returned by rollDie function to the number stored in r4
	ldr	r0, [fp, #-8]		@ Loads address of first array index into r0
	ldr	r1, [fp, #-12]		@ Loads array size into r1
	mov	r2, r4			@ Moves the value in r4 into r2

	bl	incArray		@ Calls the function to increment the correct array index

	add	r9, r9, #1		@ Increments r9 by 1
	bl	loop1			@ Branches back to the start of the loop

outloop1:

	ldr	r0, [fp, #-8]		@ Loads address of first array index into r0
	ldr	r1, [fp, #-12]		@ Loads array size into r1
	bl	printTable		@ Calls the function to print the histogram

	sub 	sp, fp, #4		@ Moves down one memory location from fp and stores it in sp
	pop 	{fp, pc}		@ Pops fp and pc from the stack