[entry: main]
[enable: logical_registers]

// Renders the Mandelbrot set as ASCII art. The evolving z value is kept in a
// Complex struct on the stack (accessed through its field offsets), while the
// per-pixel constant c stays in xmm2/xmm3. Uses double-precision floats and the
// logical_registers extension (r1..r14 name the general-purpose registers).

const SYS_WRITE = 1
const SYS_EXIT = 60
const STDOUT = 1

const W = 80
const H = 30
const MAX_ITER = 32

struct Complex
{
    re: qword
    im: qword
}

data palette = " .:-=+*#%@"

proc main
{
    stack z[Complex.size]
    stack row[W + 1]

    r11 = 0             // py

row_loop:
    // ci = py * 0.08 - 1.2
    xmm3 = r11
    xmm7 = 0.08
    xmm3 *= xmm7
    xmm7 = 1.2
    xmm3 -= xmm7

    r12 = 0             // px

col_loop:
    // cr = px * 0.04375 - 2.5
    xmm2 = r12
    xmm7 = 0.04375
    xmm2 *= xmm7
    xmm7 = 2.5
    xmm2 -= xmm7

    // z = 0 + 0i
    xmm0 = 0.0
    r5 = z
    r5 += Complex.re
    ^r5 = xmm0          // z.re = 0
    r5 = z
    r5 += Complex.im
    ^r5 = xmm0          // z.im = 0

    r2 = 0              // iteration count

iter_loop:
    // load z into xmm0 (zr) and xmm1 (zi)
    r5 = z
    r5 += Complex.re
    xmm0 = ^r5
    r5 = z
    r5 += Complex.im
    xmm1 = ^r5

    // zr2 = zr*zr, zi2 = zi*zi
    xmm4 = xmm0
    xmm4 *= xmm0
    xmm5 = xmm1
    xmm5 *= xmm1

    // escape when zr2 + zi2 > 4.0
    xmm6 = xmm4
    xmm6 += xmm5
    if xmm6 > 4.0
        goto plot

    // new_zi = 2*zr*zi + ci   (uses the old zr and zi)
    xmm6 = xmm0
    xmm6 *= xmm1
    xmm6 += xmm6
    xmm6 += xmm3
    xmm7 = xmm6         // stash new_zi

    // new_zr = zr2 - zi2 + cr
    xmm4 -= xmm5
    xmm4 += xmm2

    // store the new z back into the struct
    r5 = z
    r5 += Complex.re
    ^r5 = xmm4          // z.re = new_zr
    r5 = z
    r5 += Complex.im
    ^r5 = xmm7          // z.im = new_zi

    r2 += 1
    if r2 < MAX_ITER
        goto iter_loop

plot:
    // index = iter * 9 / MAX_ITER, then char = palette[index]
    r1 = r2
    r1 *= 9
    r3 = MAX_ITER
    r1 /= r3

    r5 = palette
    r5 += r1
    r4 = ^byte r5

    r6 = row
    r6 += r12
    ^byte r6 = r4

    r12 += 1
    if r12 < W
        goto col_loop

    // terminate the row with a newline and write it
    r6 = row
    r6 += W
    r1 = 10
    ^byte r6 = r1

    r1 = SYS_WRITE
    r6 = STDOUT
    r5 = row
    r4 = W
    r4 += 1
    syscall

    r11 += 1
    if r11 < H
        goto row_loop

    r1 = SYS_EXIT
    r6 = 0
    syscall
}