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|
; extern void clear_ships_on_screen(void);
; optimized bzero() replacement.
; the real bzero() in cc65-2.19 is 129 bytes long.
; it's optimized for speed (has an unrolled loop) and shares
; code with memset(). we can do it in a lot less code here,
; especially since we only need to clear exactly 20 bytes
; located at a known absolute address.
; in C, we could write: for(i=0; i<len; i++) { arr[i] = 0; }
; ...which takes up around 64 bytes of code.
; instead, this: clear_ships_on_screen();
; ...takes 3 bytes for the function call, plus ~20 bytes for
; the function, or around 1/3 the size of the for loop, or under 1/4
; the size of bzero() plus its function call.
; we also have clear_hkw() and clear_hold().
.import _ships_on_screen, _hkw_, _hold_
.export _no_ships_on_screen
.export _hold_is_empty, _hkw_is_empty, _have_no_cargo
.export _clear_hkw, _clear_hold, _clear_ships_on_screen
.include "atari.inc"
.code
_clear_ships_on_screen:
lda #<(_ships_on_screen-1)
ldx #>(_ships_on_screen-1)
ldy #$14
; fall thru
clr_array:
; AX is array address minus one!
; Y is sizeof(array)
sta FR0
stx FR0+1
lda #0
@l:
sta (FR0),y
dey
bne @l
rts
_clear_hkw:
lda #<(_hkw_-1)
ldx #>(_hkw_-1)
ldy #$08
bne clr_array
_clear_hold:
lda #<(_hold_-1)
ldx #>(_hold_-1)
ldy #$10
bne clr_array
;;;;;
; Several places in the Taipan C code we have to check whether an
; array is all zero. A for loop in C takes up quite a bit of space,
; so write an array-checker in asm.
; Wrappers for array_is_empty():
; no_ships_on_screen()
; hold_is_empty()
; hkw_is_empty()
; have_no_cargo();
_no_ships_on_screen:
lda #<(_ships_on_screen-1)
ldx #>(_ships_on_screen-1)
ldy #$14
; fall thru
array_is_empty:
; AX is array address minus one!
; Y is sizeof(array)
sta FR0
stx FR0+1
@l:
lda (FR0),y
bne ret0
dey
bne @l
@ret1:
lda #1
rts
ret0:
lda #0
tax ; need this or not?
rts
_hkw_is_empty:
lda #<(_hkw_-1)
ldx #>(_hkw_-1)
ldy #$08
bne array_is_empty
_hold_is_empty:
lda #<(_hold_-1)
ldx #>(_hold_-1)
ldy #$10
bne array_is_empty
_have_no_cargo:
jsr _hkw_is_empty
beq ret0
bne _hold_is_empty
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