2020/c64/btree.asm

// vim: filetype=kickass

.const next_index = $02
.const input = $03
// NOTE Assumes the tree is zeroed
tree_insert:
    ldx #0

    !loop:
        lda tree_values_lo, x
        bne !not_zero+
        lda tree_values_hi, x
        bne !not_zero+

            // Insert the node
            lda input
            sta tree_values_lo, x
            lda input + 1
            sta tree_values_hi, x

            inc next_index
            rts

    !not_zero:
        sec
        lda tree_values_lo, x
        sbc input
        lda tree_values_hi, x
        sbc input + 1
        bcc !greater+

        !less:
            lda tree_left, x
            bne !+
                lda next_index
                sta tree_left, x
            !:
            lda tree_left, x
            tax

            jmp !loop-

        !greater:
            lda tree_right, x
            bne !+
                lda next_index
                sta tree_right, x
            !:
            lda tree_right, x
            tax

            jmp !loop-

    brk


tree_contains:
    ldx #0

    !loop:
        sec
        lda tree_values_lo, x
        sbc input
        beq !lo_eq+
        lda tree_values_hi, x
        sbc input + 1
        bcc !greater+

        !less:
            lda tree_left, x
            beq !not_found+
            tax
            jmp !loop-

        !greater:
            lda tree_right, x
            beq !not_found+
            tax
            jmp !loop-

        !not_found:
            // Match not found, set 1 so bne branches
            lda #1
            rts

        !lo_eq:
            lda tree_values_hi, x
            sbc input + 1
            bne !less-

            // Match found, set 0 so beq branches
            lda #0
            rts

    brk


    .align $100
tree_values_lo:
    .fill 256, 0
tree_values_hi:
    .fill 256, 0
tree_left:
    .fill 256, 0
tree_right:
    .fill 256, 0