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|
;;;
;; list.nes - a small library to maintain big lists on the NES.
;;
;; Copyright (C) Miquel Sabaté Solà <mikisabate@gmail.com>
;;
;; This library is free software: you can redistribute it and/or modify
;; it under the terms of the GNU Lesser General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;;
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public License
;; along with this library. If not, see <https://www.gnu.org/licenses/>.
;; Initialize a new list which starts at the given 16-bit address.
.macro LIST_INIT address
lda #.lobyte(address)
sta List::ptr
sta List::last
lda #.hibyte(address)
sta List::ptr + 1
sta List::last + 1
.endmacro
;; For an already initialized list, reset the `List::ptr` variable so the list
;; can be iterated with functions like `List::get`.
.macro LIST_IT_FROM address
lda #.lobyte(address)
sta List::ptr
lda #.hibyte(address)
sta List::ptr + 1
.endmacro
;; Move the `List::ptr` variable so to point to the next element.
.macro LIST_NEXT
clc
lda #1
adc List::ptr
sta List::ptr
lda #0
adc List::ptr + 1
sta List::ptr + 1
.endmacro
;;;
;; List provides the scope for the variables and subroutines that have been
;; defined in order to maintain and manipulate big lists on the NES.
;;
;; This library can also work for smaller lists but there are other more
;; performant ways to achieve the same thing. Thus, use this library only if you
;; need to have a list that may store more than 255 bytes and indexing in the
;; usual ways might be a problem otherwise.
;;
;; For more information on the usage and the API check the documentation
;; (README.md file on the https://git.mssola.com/nes/list.nes repository).
.scope List
;; NOTE (important): this library needs 4 bytes to store information of this
;; list. These are two 16-bit pointers which are used for the subroutines
;; being defined here. The exact location of these pointers are set to
;; $60-$63 by default, but they can be changed by providing definitions for
;; `LIST_PTR_ADDRESS` and `LIST_LAST_ADDRESS`.
.ifdef LIST_PTR_ADDRESS
ptr = LIST_PTR_ADDRESS
.else
ptr = $60
.endif
.ifdef LIST_LAST_ADDRESS
last = LIST_LAST_ADDRESS
.else
last = $62
.endif
;; Set the value of `a` into the list and advance one position without
;; growing the list.
;;
;; Use this function instead of `List::push` if you have already set
;; `List::ptr` as desired (e.g. with `LIST_IT_FROM`) and you just want to
;; set a specific value to this address. That is, the list has already been
;; defined somewhere else and you are just modifying some position.
;;
;; If the list pointer is already at the end and the operation is not
;; possible, then `y` is set to $FF, otherwise `y` will be set to 0.
;;
;; NOTE: registers modified: `a` and `y`.
.proc set
tay
;; Check if `List::ptr` >= `List::last` (16-bit comparison). If this is
;; the case, then we are actually done, otherwise we can proceed to set
;; the value as desired.
lda List::ptr + 1
cmp List::last + 1
bcc @do
bne @done
lda List::ptr
cmp List::last
bcc @do
@done:
;; We were actually done: set `y` to `$FF` to denote "end of list".
ldy #$FF
lda #0
rts
@do:
tya
ldy #0
sta (List::ptr), y
LIST_NEXT
rts
.endproc
;; Push the value of `a` after the last position of the list and grow one
;; more byte.
;;
;; Note that this subroutine assumes that we are already at the last item of
;; the list. Hence, if you reset `List::ptr` (e.g. with `LIST_IT_FROM`) and
;; then call this subroutine, you will also move the `List::last` pointer
;; accordingly and thus you might have (accidentally) shrinked the list. If
;; this is not a behavior that you want (you just want to set a value at a
;; specific location), then take a look at `List::set` instead.
;;
;; NOTE: registers modified: `a` and `y`.
;; NOTE: this subroutine might set the carry flag.
.proc push
ldy #0
sta (List::ptr), y
clc
lda #1
adc List::ptr
sta List::ptr
sta List::last
lda #0
adc List::ptr + 1
sta List::ptr + 1
sta List::last + 1
rts
.endproc
;; Get the contents of the current position of the list pointer and advance
;; it.
;;
;; The byte will be stored into the 'a' register. If the list pointer is
;; already at the end and won't fetch relevant data, then `y` is set to $FF,
;; otherwise `y` will be set to 0.
;;
;; NOTE: registers modified: 'a' and 'y'.
;; NOTE: this subroutine might set the carry flag.
.proc get
;; Check if `List::ptr` >= `List::last` (16-bit comparison). If this is
;; the case, then we are actually done, otherwise we can proceed to
;; fetch the value as desired.
lda List::ptr + 1
cmp List::last + 1
bcc @do
bne @done
lda List::ptr
cmp List::last
bcc @do
@done:
;; We were actually done: set `y` to `$FF` to denote "end of list" and
;; zero out the returned value.
ldy #$FF
lda #0
rts
@do:
;; Fetch the value and push it into the stack since `LIST_NEXT` will
;; actually mess with the `a` register.
ldy #0
lda (List::ptr), y
pha
LIST_NEXT
;; Get the value back from the stack so to set the proper return value.
pla
rts
.endproc
.endscope
|
