write a specific memset only for clearing screen, so we can make it faster!

wip-hugo/routines/memory/clear_screen.s

@@ -0,0 +1,39 @@
+;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
+
+;; Sets memory in 'A'-registry to all addresses from 'A_start' until 'A_start' + 'length'
+;; Modifies A, X and A_start
+.proc clear_screen
+        .include "mem.inc"
+        VIC_bank = $4000
+        length_ = $1f40
+        low_length_3 = $C0 + $03 ;; we need one more.
+        Mov_16 A_start, A_start + 1, #<VIC_bank, #>VIC_bank
+        LDA #$00
+        ;; big_set sets the memory in $ff chunks.
+        ;; skipp if length >= $ff
+        LDX #>length_
+        BNE big_set
+        JMP small_set
+big_set: ;sets $ff of memory
+        ;; Y value do not matter, will go through all anyway!
+        .repeat $ff
+        STA (A_start), Y
+        DEY
+        .endrepeat
+        STA (A_start), Y ; dont forget Y =0
+big_set_end:
+        ;;set all hole $ff memory chunks!
+        INC A_start + 1
+        DEX ;; length +1 --
+        BEQ small_set
+        JMP big_set
+
+small_set:
+        LDX big_set + low_length_3
+        LDY #$60
+        STY big_set + low_length_3
+        LDY #<length_
+        JSR big_set
+        STX big_set + low_length_3
+        RTS
+.endproc