2020/c64/math.inc

// vim: filetype=kickass

.macro i8_div5_a() {
    sta zp_temp
    lsr
    adc #13
    adc zp_temp
    ror
    lsr
    lsr
    adc zp_temp
    ror
    adc zp_temp
    ror
    lsr
    lsr
}

.macro i16_div8(lo, hi) {
    lsr cursor_pointer_hi
    ror cursor_pointer_lo

    lsr cursor_pointer_hi
    ror cursor_pointer_lo

    lsr cursor_pointer_hi
    ror cursor_pointer_lo
}

//
// u16_div10
//
// Divides an unsigned 16-bit integer by 10.
//
// d = n * (1 / 10)
//   = floor(n * floor(65536 / 10) / 65536)
//   = floor(n * 6553 / 65536)
//   = floor(n * 6553 >> 16)
//
// Input:
//  - $03..$04 - 16-bit unsigned value
//  - Generated multiplication table
//
// Output:
//  - $24..$25 - 16-bit unsigned result
//
// Destroys: a, x, $22..$25, $fd, $fe
//
.macro u16_div10() {
    lda #$19
    sta $fe
    lda #$99
    sta $fd

    sec
    jsr multiply_16bit_unsigned
}

.macro i8_mul5_a() {
    sta zp_temp
    asl
    asl
    clc
    adc zp_temp
}

// Destroys: lo, hi
.macro i16_mul2(lo, hi) {
    asl lo
    rol hi
}

// Destroys: lo, hi
.macro i16_mul4(lo, hi) {
    i16_mul2(lo, hi)
    i16_mul2(lo, hi)
}

// Destroys: lo, hi
.macro i16_mul8(lo, hi) {
    i16_mul4(lo, hi)
    i16_mul2(lo, hi)
}

// Destroys: a, lo, hi, $fd, $fe
.macro i16_mul10(lo, hi) {
    i16_mul2(lo, hi)

    lda lo
    sta $fd
    lda hi
    sta $fe

    i16_mul4(lo, hi)
    i16_i16_add(lo, hi, $fd, $fe)
}

// Destroys: a, dst_lo, dst_hi
.macro i16_i8_add_a(dst_lo, dst_hi) {
    clc
    adc dst_lo
    sta dst_lo
    bcc !cc+
    inc dst_hi
!cc:
}

// Destroys: a, dst_lo, dst_hi
.macro i16_i16_add(dst_lo, dst_hi, src_lo, src_hi) {
    clc
    lda dst_lo
    adc src_lo
    sta dst_lo
    lda dst_hi
    adc src_hi
    sta dst_hi
}

// Destroys: a, dst_lo, dst_hi
.macro i16_inc(lo, hi) {
    lda #1
    i16_i8_add_a(lo, hi)
}

.macro i16_i16_sub_imm(dst_lo, dst_hi, src_lo, src_hi, imm) {
    sec

    lda src_lo
    sbc #<imm
    sta dst_lo

    lda src_hi
    sbc #>imm
    sta dst_hi
}

// Destroys: a
.macro i16_i16_sub(dst_lo, dst_hi, a_lo, a_hi, b_lo, b_hi) {
    sec

    lda a_lo
    sbc b_lo
    sta dst_lo
    lda a_hi
    sbc b_hi
    sta dst_hi
}

.macro i16_imm_i16_sub(dst_lo, dst_hi, imm, src_lo, src_hi) {
    lda src_lo
    eor #$ff
    sec
    adc #<imm
    sta dst_lo

    lda src_hi
    eor #$ff
    adc #>imm
    sta dst_hi
}

.macro i16_i16_cmp_bne(a_lo, a_hi, b_lo, b_hi, target) {
    lda a_lo
    cmp b_lo
    bne target
    lda a_hi
    cmp b_hi
    bne target
}