2020/c64/math.inc

// vim: filetype=kickass
.const udivmod32_dividend = $10 // 11,12,13
.const udivmod32_divisor = $14 // 15,16,17
.const udivmod32_result = $18 // 19,1a,1b
.const udivmod32_remainder = $1c // 1d,1e,1f

.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, $fd, $fe
.macro i16_mul10(dst) {
    i16_mul2(dst, dst + 1)

    lda dst
    sta $fd
    lda dst + 1
    sta $fe

    i16_mul4(dst, dst + 1)
    i16_i16_add(dst, $fd)
}

.macro u32_mul2(lsb) {
    asl lsb + 0
    rol lsb + 1
    rol lsb + 2
    rol lsb + 3
}

.macro u32_mul10(lsb) {
    u32_mul2(lsb)

    lda lsb + 0
    sta $2c + 0
    lda lsb + 1
    sta $2c + 1
    lda lsb + 2
    sta $2c + 2
    lda lsb + 3
    sta $2c + 3

    u32_mul2(lsb)
    u32_mul2(lsb)

    i32_i32_add(lsb, $2c)
}

.macro i32_i16_add(dst, src) {
    clc
    lda dst + 0
    adc src + 0
    sta dst + 0
    lda dst + 1
    adc src + 1
    sta dst + 1
    bcc !+
    inc dst + 2
!:
}

.macro i32_i32_add(dst, src) {
    clc
    lda dst + 0
    adc src + 0
    sta dst + 0
    lda dst + 1
    adc src + 1
    sta dst + 1
    lda dst + 2
    adc src + 2
    sta dst + 2
    lda dst + 3
    adc src + 3
    sta dst + 3
}

// Destroys: a
.macro i16_i8_add_a(dst) {
    clc
    adc dst
    sta dst
    bcc !cc+
    inc dst + 1
!cc:
}

// Destroys: a
.macro i16_i16_add(dst, src) {
    clc
    lda dst
    adc src
    sta dst
    lda dst + 1
    adc src + 1
    sta dst + 1
}

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

.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, imm, src) {
    lda src
    eor #$ff
    sec
    adc #<imm
    sta dst

    lda src + 1
    eor #$ff
    adc #>imm
    sta dst + 1
}

.macro i16_i16_cmp_bne(a, b, target) {
    lda a
    cmp b
    bne target
    lda a + 1
    cmp b + 1
    bne target
}