project in z80

Project:
;hl is Z, de is Y, bc is X
;hl<32768, if hl is sup - return early
    add hl, hl
; return if neg
    ret c
    ld  a, h
    or  a
    jr  z, _scale_up
_scale_down_loop:
    srl a
    rr  l
    sra d
    rr  e
    sra b
    rr  c
    or  a
    jp  nz, _scale_down_loop
_scale_up:
;l, e, c are significant
    ld  a, l
    or  a
    ret z
    cp  98
    jp  z, _no_bissect
    jr  nc, _scale_done
_scale_up_loop:
    sla e
    sla c
    add a, a
    cp  98
    jp  c, _scale_up_loop
_scale_done:
    rra
    ld  l, a
; l = Z, e = X, c = Y
    xor a
    ld  h, a
    ld  d, a
    ld  b, a
#macro  bissect_iter()
    ld  a, l
    add a, h
    srl a
    cp  49
; calculate midpoint and classify
    jr  nc, $+18
; store to h
    ld  h, a
    ld  a, e
    add a, d
    inc a
    sra a
    ld  d, a
    ld  a, c
    add a, b
    inc a
    sra a
    ld  b, a
    jp  $+16
; store it to l
    ld  l, a
    ld  a, e
    add a, d
    inc a
    sra a
    ld  e, a
    ld  a, c
    add a, b
    inc a
    sra a
    ld  c, a
#endmacro

; 6 iter to match precision
bissect_iter()
bissect_iter()
bissect_iter()
bissect_iter()
bissect_iter()
bissect_iter()

; finish:

    ld  a, e
    add a, d
    inc a
    sra a
    add a, 48
; or whatever
    ld  (gScreenX), a
    ld  a, c
    add a, b
    inc a
    sra a
    ld  c, a
    ld  a, 32
    sub c
    ld  (gScreenY), a
    ret
_no_bissect:
    ld  a, e
    add a, 48
    ld  (gScreenX), a
    ld  a, 32
    sub c
    ld  (gScreenY), a
    ret