collapseos/apps/zasm/io.asm
Virgil Dupras 7083116379 zasm: remove JUMP_ prefixes
They serve no purpose and make the code less flexible.
2019-05-17 09:50:11 -04:00

168 lines
4.4 KiB
NASM

; I/Os in zasm
;
; As a general rule, I/O in zasm is pretty straightfoward. We receive, as a
; parameter, two blockdevs: One that we can read and seek and one that we can
; write to (we never seek into it).
;
; zasm doesn't buffers its reads during tokenization, which simplifies its
; process. However, it also means that it needs, in certain cases, a "putback"
; mechanism, that is, a way to say "you see that character I've just read? that
; was out of my bounds. Could you make it as if I had never read it?". That
; buffer is one character big and is made with the expectation that ioPutBack
; is always called right after a ioGetC (when it's called).
;
; ioPutBack will mess up seek and tell offsets, so thath "put back" should be
; consumed before having to seek and tell.
;
; That's for the general rules.
;
; Now, let's enter includes. To simplify processing, we make include mostly
; transparent to all other units. They always read from ioGetC and a include
; directive should have the exact same effect as copy/pasting the contents of
; the included file in the caller.
;
; By the way: we don't support multiple level of inclusion. Only top level files
; can include.
;
; When we include, all we do here is open the file with fsOpen and set a flag
; indicating that we're inside an include. When that flag is on, GetC, Seek and
; Tell are transparently redirected to their fs* counterpart.
;
; When we reach EOF in an included file, we transparently unset the "in include"
; flag and continue on the general IN stream.
; *** Variables ***
.equ IO_IN_GETC IO_RAMSTART
.equ IO_IN_PUTC IO_IN_GETC+2
.equ IO_IN_SEEK IO_IN_PUTC+2
.equ IO_IN_TELL IO_IN_SEEK+2
.equ IO_OUT_GETC IO_IN_TELL+2
.equ IO_OUT_PUTC IO_OUT_GETC+2
.equ IO_OUT_SEEK IO_OUT_PUTC+2
.equ IO_OUT_TELL IO_OUT_SEEK+2
; Save pos for ioSavePos and ioRecallPos
.equ IO_SAVED_POS IO_OUT_TELL+2
; File handle for included source
.equ IO_INCLUDE_HDL IO_SAVED_POS+2
; see ioPutBack below
.equ IO_PUTBACK_BUF IO_INCLUDE_HDL+FS_HANDLE_SIZE
.equ IO_IN_INCLUDE IO_PUTBACK_BUF+1
.equ IO_RAMEND IO_IN_INCLUDE+1
; *** Code ***
ioInit:
xor a
ld (IO_PUTBACK_BUF), a
ld (IO_IN_INCLUDE), a
ret
ioGetC:
ld a, (IO_PUTBACK_BUF)
or a ; cp 0
jr nz, .getback
call ioInInclude
jr z, .normalmode
; We're in "include mode", read from FS
push de
ld de, IO_INCLUDE_HDL
call fsGetC
pop de
or a ; cp 0
ret nz ; not zero, all good
; We reached EOF. What we do depends on whether we're in Local Pass
; mode. Yes, I know, a bit hackish. Normally, we *should* be
; transparently getting of include mode and avoid meddling with global
; states, but here, we need to tell main.asm that the local scope if
; over *before* we get off include mode, otherwise, our IO_SAVED_POS
; will be wrong (an include IO_SAVED_POS used in global IN stream).
call zasmIsLocalPass
ld a, 0 ; doesn't affect Z flag
ret z ; local pass? return EOF
; regular pass (first or second)? transparently get off include mode.
ld (IO_IN_INCLUDE), a ; A already 0
; continue on to "normal" reading. We don't want to return our zero
.normalmode:
; normal mode, read from IN stream
ld ix, (IO_IN_GETC)
jp (ix)
.getback:
push af
xor a
ld (IO_PUTBACK_BUF), a
pop af
ret
; Put back non-zero character A into the "ioGetC stack". The next ioGetC call,
; instead of reading from IO_IN_GETC, will return that character. That's the
; easiest way I found to handle the readWord/gotoNextLine problem.
ioPutBack:
ld (IO_PUTBACK_BUF), a
ret
ioPutC:
ld ix, (IO_OUT_PUTC)
jp (ix)
ioSavePos:
call _ioTell
ld (IO_SAVED_POS), hl
ret
ioRecallPos:
ld hl, (IO_SAVED_POS)
jr _ioSeek
ioRewind:
ld hl, 0
jr _ioSeek
; always in absolute mode (A = 0)
_ioSeek:
call ioInInclude
ld a, 0 ; don't alter flags
jr nz, .include
; normal mode, seek in IN stream
ld ix, (IO_IN_SEEK)
jp (ix)
.include:
; We're in "include mode", seek in FS
push de
ld de, IO_INCLUDE_HDL
call fsSeek
pop de
ret
_ioTell:
call ioInInclude
jp nz, .include
; normal mode, seek in IN stream
ld ix, (IO_IN_TELL)
jp (ix)
.include:
; We're in "include mode", tell from FS
push de
ld de, IO_INCLUDE_HDL
call fsTell
pop de
ret
; Sets Z according to whether we're inside an include
ioInInclude:
ld a, (IO_IN_INCLUDE)
or a ; cp 0
ret
; Open include file name specified in (HL).
; Sets Z on success, unset on error.
ioOpenInclude:
call fsFindFN
ret nz
ld hl, IO_INCLUDE_HDL
call fsOpen
ld a, 1
ld (IO_IN_INCLUDE), a
cp a ; ensure Z
ret