;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-

;;Moves data from buffer A to B.
;; Buffer A starts at 'A_start' and B starts att 'B_start'.
;; The data has length 'length'.
.proc memcpy
        .include "mem.inc"
        LDY #$00
loop:
        LDA (B_start), Y
        STA (A_start), Y
        INY
        BEQ y_overflow
change_length:
        DEC length
        BNE loop

        DEC length +1
        BPL loop
        RTS
y_overflow:
        ;; Y is now 0
        INC B_start + 1
        INC A_start + 1

        jmp change_length
.endproc