implement general divition

wip-hugo/routines/arithmatic/arithmatic.inc

@@ -1,4 +1,5 @@
 ;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
 ;; public args
-VAL_A = ARGVEC + 0
-VAL_B = ARGVEC + 1
+VAL_B = ARGVEC + 0
+VAL_A = ARGVEC + 1
+;; Note that we use VAL_A +1 as a temp variable, this is a hack to make it faster.

wip-hugo/routines/arithmatic/div.s

@@ -0,0 +1,43 @@
+;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
+.proc div; user-procedure :clobbers (A,X) :clobbers-arguments 3
+        ;; https://en.wikipedia.org/wiki/Division_algorithm#Restoring_division
+        ;;VAL_A / VAL_B = X
+        ;; Remainder (after) = VAL_A
+        ;; only works if VAL_A > VAL_B
+
+        ;; Because the algorithm R needs to be signed 16-bit
+        ;; We make it unsigned by storing the sign-bit in the branching.
+        .include "arithmatic.inc"
+        R = VAL_A
+        LDA #$00
+        STA VAL_A + 1
+        D = VAL_B
+        count =$E0
+
+        LDA #%10000000
+        STA count ;; this is 2^i
+        LDX #$00
+for_i:; for i in 7-0 do
+        ;; R = R*2 -D*2^8
+        ;; R*2
+        Mult_16 R, R + 1
+
+        ;; -D* 2^8
+        SEC
+        LDA R + 1
+        SBC D
+        BMI R_neg
+        STA R + 1
+R_pos: ; R >= 0
+        ;; X(i) = 1
+        TXA
+        EOR count
+        TAX
+R_neg: ; R < 0
+;; We need to take back R
+;; We did that by not saving the arithmatic :)
+        LSR count
+        BNE for_i
+for_i_end:
+        RTS
+.endproc

wip-hugo/routines/arithmatic/div_test.s

@@ -0,0 +1,10 @@
+;;; -*- Mode: asm; indent-tabs-mode: t; tab-width: 8 -*-
+;;Calculates $EE /$05 = $33
+.scope div_test
+        .include "arithmatic.inc"
+        LDA #$05
+        STA VAL_A
+        LDA #$02
+        STA VAL_B
+        JSR div; X = $02 if it works as it should
+.endscope

wip-hugo/source.s

@@ -8,7 +8,8 @@
 .include "STARTUP.s"
 ;.include "dubbel_buffer/raster_irqs.s"
 
-.include "routines/arithmatic/mult_test.s"
+;.include "routines/arithmatic/mult_test.s"
+.include "routines/arithmatic/div_test.s"
 ;.include "routines/line/line_test.s"
 ;.include "routines/text/char_draw_test.s"
 ;.include "routines/pixel/pixel_test.s"
@@ -25,4 +26,5 @@ JMP exit
 .include "routines/memory/memset.s"
 .include "routines/memory/memcpy.s"
 .include "routines/arithmatic/mult.s"
+.include "routines/arithmatic/div.s"
 .include "END.s"