; 16-bit floats have an 11-bit signed value and a 5-bit signed precision.

; These control codes are required by the standard.
F16_INF    EQU $7BFF
F16_NEGINF EQU $7FFF
F16_NAN    EQU $FFFF

CastFloat16ToFixed48:
; de: f16
; hl: q48 *
; returns to *hl

; Arithmetically right-shift the precision
	ld b, d
	sra b
	sra b
	sra b

; Mask away the precision and extend the sign of the value
	ld a, d
	and $7
	bit 2, a
	jr z, .no_sign_extend
	or $f8
.no_sign_extend
	ld d, a

; Prepare the output buffer.  Fixed, big-endian 48-bit numbers have the binary point 32 bits in.
	ld a, 0
	jr z, .no_output_sign_extend
	dec a
.no_output_sign_extend
; Sign extend
	push hl
	ld [hli], a
	ld [hli], a
; Load the input float
	ld [hl], d
	inc hl
	ld [hl], e
	inc hl
; Fill the rest with 0
	xor a
	ld [hli], a
	ld [hl], a
	pop hl

; If the precision is 0, no shifting is needed
	ld a, b
	and a
	ret z
; Check the sign of the precision
	bit 7, a
	jr z, .precision_positive
; Right-shift to gain the required fixed-point precision
	cpl
	inc a
	ld b, a
	ld c, 6
.neg_prec_outer
	push hl
	push bc
	and a
.neg_prec_inner
	rr [hl]
	inc hl
	dec c
	jr nz, .neg_prec_inner
	pop bc
	pop hl
	dec b
	jr nz, .neg_prec_outer
	ret

.precision_positive
; Left-shift to gain the required fixed-point magnitude
	push hl
	ld de, 5
	add hl, de
	ld c, 6
.pos_prec_outer
	push hl
	push bc
	and a
.pos_prec_inner
	rl [hl]
	dec hl
	dec c
	jr nz, .pos_prec_inner
	pop bc
	pop hl
	dec b
	jr nz, .pos_prec_outer
	pop hl
	ret

CastFixed48ToFloat16:
; hl: q48 *
; returns f16 de
	bit 7, [hl]
	push af ; save sign
	jr z, .positive
	; take absolute value
	push hl
	ld c, 6
.cpl_loop
	ld a, [hl]
	cpl
	ld [hli], a
	dec c
	jr nz, .cpl_loop
	dec hl
	inc [hl]
	pop hl
.positive
	; find most significant position
	ld b, 16
.most_significant_position_loop
	ld c, 8
	ld a, [hli]
.most_significant_position_loop_inner
	add a
	jr c, .got_most_significant_position
	dec b
	dec c
	jr nz, .most_significant_position_loop
	jr .most_significant_position_loop

.got_most_significant_position
	push bc
	; calculate the shift
	ld a, b
	bit 7, a
	jr z, .shift_left
	cpl
	inc a
	ld b, a
	cp 16
	jr c, .shift_right
	; can't fit in an f16, return 0
	ld de, 0
	add sp, 4
	ret

.shift_left
	cp 11
	jr c, .okay_shift_left
	; can't fit in an f16, return infinity
	ld de, F16_INF
	pop af
	pop af
	ret z
	set 2, d
	ret

.okay_shift_left
	ld de, 5
	add hl, de
	inc e
	ld c, e
.shift_left_loop_outer
	push bc
	and a
.shift_left_loop_inner
	rl [hl]
	dec hl
	dec c
	jr nz, .shift_left_loop_inner
	pop bc
	add hl, de
	dec b
	jr nz, .shift_left_loop_outer
	inc hl
	jr .pack

.shift_right
	ld de, -6
	ld c, 6
.shift_right_loop_outer
	push bc
	and a
.shift_right_loop_inner
	rr [hl]
	inc hl
	dec c
	jr nz, .shift_right_loop_inner
	pop bc
	add hl, de
	dec b
	jr nz, .shift_right_loop_outer
.pack
	pop bc
	sla b
	sla b
	sla b
	inc hl
	inc hl
	ld a, [hli]
	ld e, [hl]
	and $3
	ld d, a
	pop af
	jr z, .no_cpl
	ld a, d
	cpl
	and $7
	ld d, a
	ld a, e
	cpl
	inc a
	ld e, a
.no_cpl
	ld a, d
	or b
	ld d, a
	ret