2020/c64/day01.asm

// vim: filetype=kickass

* = * "Day 01"


//
// day01
//
// Destroys:
//   a, x, y, $02..$04, $10..$1c, $20..$25, $fd..$fe, everything you've ever loved
//
.const input_pointer  = $20
.const atoi_result    = $03  // Needs to be $03 for tree_insert

.const loop_pointer = $20
.const remainder    = $24

// Need to be $26 and $fd due to multiply_16bit_unsigned
.const outer_value    = $26
.const inner_value    = $fd

day01:
    move_16_imm($03, str_title)
    jsr write_string

    //
    // Parse the input at day01_input into an array of integers.
    //
    move_16_imm(input_pointer, day01_input)
    ldy #0

!line:
    // Create a temporary 16-bit integer to store the result in
    // in between digits.
    move_16_imm(atoi_result, 0)

!digit:
    // Check for the newline character at the end of the line.
    lda (input_pointer), y
    cmp #'\n'
    beq !newline+

    // Multiply the stored number by 10.
    i16_mul10(atoi_result)

    // Subtract '0' from the current digit to convert it to "binary".
    lda (input_pointer), y
    sec
    sbc #'0'

    // Add the binary digit to the stored number
    i16_i8_add_a(atoi_result)

    // Increment y.
    iny
    bne !digit-

    // If y overflows, increment the MSB of the input pointer as well,
    // for a 16-bit increment.
    inc input_pointer + 1
    jmp !digit-

!newline:
    // Insert the converted number into the tree.
    jsr tree_insert

    iny
    bne !+
        inc input_pointer + 1
    !:

    // Check for the null terminator.
    lda (input_pointer), y
    bne !line-

    move_16_imm($03, str_parse_done)
    jsr write_string

    ldy #0
    !loop:
        // Subtract the number from 2020 to find the needed value.
        lda tree_values_lo, y
        sta $fd
        eor #$ff
        sec
        adc #<2020
        sta $03
        sta $26

        lda tree_values_hi, y
        sta $fe
        eor #$ff
        adc #>2020
        sta $04
        sta $27

        iny
        jsr tree_contains
        bne !loop-

    // Multiply the results together
    sec
    jsr multiply_16bit_unsigned

    move_16_imm($03, str_calc_done)
    jsr write_string

    // Print the 32-bit result as decimal.
    lda $25
    sta udivmod32_dividend + 3
    lda $24
    sta udivmod32_dividend + 2
    lda $23
    sta udivmod32_dividend + 1
    lda $22
    sta udivmod32_dividend + 0
    jsr print_decimal_u32

    rts

!error:
    move_16_imm($03, str_no_result)
    jsr write_string
    rts


str_title:
    .text "# Day 01, part 1:"
    .byte '\n', 0

str_parse_done:
    .text "* Finished parsing"
    .byte '\n', 0

str_calc_done:
    .text "* Finished calculating"
    .byte '\n', 0

str_no_result:
    .byte '\n'
    .text "! Could not find a result"
    .byte '\n', 0