;;; -*- 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