.org 0x08000000

        b ProgramStart

        ;cartridge header goes here


;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;	
; Program Start

	.equ ramarea, 0x02000000
	.equ CursorX,ramarea		
	.equ CursorY,ramarea+1
	.equ hailstoneram,0x02000004
	
	
ProgramStart:
	mov sp,#0x03000000			;Init Stack Pointer
	
	mov r4,#0x04000000  		        ;DISPCNT - LCD Video Controller
	mov r2,#0x403    			;4= Layer 2 on / 3= ScreenMode 3
	str	r2,[r4]         	        ;now the user can see the screen

	bl ResetTextCursors			;set text cursors to top left of screen. This routine, as well as the other I/O
	                                        ;     routines, were omitted to keep this entry short.
	mov r0,#27
	adr r1,HailStoneMessage_Init
	bl PrintString
	bl NewLine
	bl ShowHex32
	bl NewLine
	bl NewLine
	
	
	bl Hailstone
	
                ;function is complete, return the output
	        adr r1,HailStoneMessage_0
		bl PrintString
		bl NewLine
		ldr r1,HailStoneRam_Mirror		;mov r2,0x02000004
		
		
		ldr r0,[r1],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r1],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r1],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r1],#4
		bl ShowHex32
		bl NewLine
		bl NewLine
		
		adr r1,HailStoneMessage_1
		bl PrintString
		bl NewLine
		
		ldr r0,[r2],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r2],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r2],#4
		bl ShowHex32
		bl NewLine
		
		ldr r0,[r2],#4
		bl ShowHex32
		bl NewLine
		bl NewLine
		
		adr r1,HailStoneMessage_2
		bl PrintString
		bl NewLine
		mov r0,r3
		bl ShowHex32	

forever:
	b forever              ;we're done, so trap the program counter.
	
Hailstone:
	;input: R0 = n.
	;out: 	r2 = pointer to last 4 entries
	;	r3 = length of sequence
	
	
	;reg usage:
	;R1 = scratchpad
	;R3 = counter for entries in the sequence.
	;R5 = pointer to output ram
	stmfd sp!,{r4-r12,lr}

		mov r5,#0x02000000
		add r5,r5,#4
		str r0,[r5],#4				;store in hailstone ram and post-inc by 4
		mov r3,#0
loop_hailstone:
		add r3,r3,#1				;represents number of entries in the sequence
		cmp r0,#1
		beq hailstone_end
		tst r0,#1
		;;;; executes only if r0 was even
		moveq r0,r0,lsr #1			;divide 		
		
		;;;; executes only if r0 was odd
		movne r1,r0
		movne r0,r0,lsl #1
		addne r0,r1,r0
		addne r0,r0,#1
		
		str r0,[r5],#4			;store in hailstone ram, post inc by 4
		
		b loop_hailstone
		
		
hailstone_end:
		sub r5,r5,#16			;subtract 16 to get pointer to last 4 entries.
		mov r2,r5				;output ptr to last 4 entries to r2.
		;pointer to first 4 entries is 0x02000004
		ldmfd sp!,{r4-r12,pc}
	
HailStoneRam_Mirror:
	.long 0x02000004
HailstoneMessage_Init:
	.byte "Your input was:",255
	.align 4
HailstoneMessage_0:
	.byte "First 4 numbers are:",255
	.align 4
HailstoneMessage_1:
	.byte "Last 4 numbers are:",255
	.align 4	
HailstoneMessage_2:
	.byte "Sequence length is:",255
	.align 4

;;;;;;;;;;; EVERYTHING PAST THIS POINT IS JUST I/O ROUTINES FOR PRINTING NUMBERS AND WORDS TO THE GAME BOY ADVANCE'S SCREEN
;;;;;;;;;;; I ASSURE YOU THAT ALL OF IT WORKS BUT CHANCES ARE YOU DIDN'T COME HERE TO SEE THAT.
;;;;;;;;;;; THANKS TO KEITH OF CHIBIAKUMAS.COM FOR WRITING THEM!