FizzBuzz

; FizzBuzz for 4Chan anons :)
;
                ;       R0 - Current number
                ;       R1 - Current number (copy)
                ;       R2 - Mod value
                ;       R3 - Mod sucess
                ;       R4 - Memory Address
                ;       R5 - Fizz
                ;       R6 - Buzz
                ;       R7 - Newline
                ;       R8 - Temp, used for moving data round
char_F          EQU     0x46
char_I          EQU     0x69
char_Z          EQU     0x7A
char_B          EQU     0x42
char_U          EQU     0x75
NEWLINE         EQU     0x0A

main
                ;       ----- SETUP REGISTERS ----- ;

                ;       Stores the beginning address of the RAM in R4
                MOV     R4, #0x10000

                ;       Store Fizz in R5
                MOV     R8, #char_F
                STRB    R8, [R4]
                MOV     R8, #char_I
                STRB    R8, [R4, #1]
                MOV     R8, #char_Z
                STRB    R8, [R4, #2]
                MOV     R8, #char_Z
                STRB    R8, [R4, #3]
                LDR     R5, [R4]

                ;       Store Buzz in R6
                MOV     R8, #char_B
                STRB    R8, [R4]
                MOV     R8, #char_U
                STRB    R8, [R4, #1]
                LDR     R6, [R4]

                ;       Store Newline in R7
                MOV     R7, #NEWLINE


                ;       Set up the FizzBuzz counter and run the loop
                MOV     R0, #100
                B       _fizzBuzzLoop



_mod_loop
                SUB     R1, R1, R2
                CMP     R1, #0
                BGT     _mod_loop           ; If we still have numbers left, keep looping
                BLT     _return_false       ; The mod flag will be false as R3 does not fit into R1
                MOV     R3, #1              ; Set the mod flag to true

_return_false
                MOV     PC, R14             ; Return to the branch link





_fizzBuzzLoop
                ;       Test FizzBuzz (%15)
                MOV     R1, R0
                MOV     R2, #15
                BL      _mod_loop
                CMP     R3, #1
                BEQ     _write_FizzBuzz

                ;       Test Fizz (%5)
                MOV     R1, R0
                MOV     R2, #5
                BL      _mod_loop
                CMP     R3, #1
                BEQ     _write_Fizz

                ;       Test Buzz (%3)
                MOV     R1, R0
                MOV     R2, #3
                BL      _mod_loop
                CMP     R3, #1
                BEQ     _write_Buzz

                ;       All test failed, write the normal number
                STR     R0, [R4]
                B       _write_Newline


_write_Fizz
                STR     R5, [R4]
                B       _write_Newline
_write_Buzz
                STR     R6, [R4]
                B       _write_Newline
_write_FizzBuzz
                STR     R5, [R4]
                ADD     R4, R4, #8
                STR     R6, [R4]
                ;       Fallthrough
_write_Newline
                ADD     R4, R4, #8
                STRB    R7, [R4]
                ADD     R4, R4, #8

                MOV     R3, #0      ; Reset the Mod register
                SUB     R0, R0, #1  ; Decrement R0
                CMP     R0, #0      ; Check if we are done
                BGT     _fizzBuzzLoop

                END