Category : C++ Source Code
Archive : VCCRT2.ZIP
Filename : _FILBUF.ASM
Output of file : _FILBUF.ASM contained in archive : VCCRT2.ZIP
title _filbuf - fill buffer and get character
;***
;_filbuf.asm - fill buffer and get character
;
; Copyright (c) 1985-1992, Microsoft Corporation. All rights reserved.
;
;Purpose:
; defines _filbuf() - fill buffer and read first character, allocate
; buffer if there is none. Used by the getc() macro. Also directly
; referenced in FREAD.ASM.
;
;*******************************************************************************
;
; --- C VERSION OF ROUTINE
;
; #include
; #include
; #include
; #include
; #include
; #include
; #include
; #ifdef MTHREAD
; #include
; #endif
;
;
; int cdecl _LOAD_DS
; _filbuf (str)
; FILE *str;
; {
; REG1 FILE _NEAR_ *stream;
; REG2 FILE2 _NEAR_ *stream2;
;
; assert(str,"str==NULL");
;
; /* Init pointer to _iob2 entry. */
; stream = (FILE _NEAR_ *) FP_OFF(str);
; stream2 = &(_iob2_(stream));
;
; if (!inuse(stream) || stream->_flag & _IOSTRG)
; return(EOF);
;
; if (stream->_flag & _IOWRT) {
; stream->_flag |= _IOERR;
; return(EOF);
; }
;
; stream->_flag |= _IOREAD;
;
; /* Get a buffer, if necessary. */
;
; if (!anybuf2(stream,stream2))
; _getbuf(stream);
; else
; stream->_ptr = stream->_base;
;
; stream->_cnt = _read(fileno(stream), stream->_base, stream2->_bufsiz);
;
; if ((stream->_cnt == 0) || (stream->_cnt == -1)) {
; stream->_flag |= stream->_cnt ? _IOERR : _IOEOF;
; stream->_cnt = 0;
; return(EOF);
; }
;
; if ( !(stream->_flag & (_IOWRT|_IORW))
; && ((_osfile[fileno(stream)] & (FTEXT|FEOFLAG)) == (FTEXT|FEOFLAG)) )
; stream2->_flag2 |= _IOCTRLZ;
;
; stream->_cnt--;
;
; return(0xff & *stream->_ptr++);
; }
;
; --- END OF C VERSION
;
.xlist
include version.inc
include cmacros.inc
include stdio.inc
include msdos.inc
.list
sBegin data
assumes ds,data
externW _iob
externW _iob2
externB _osfile ; array of handle attributes
sEnd data
externNP _getbuf ; buffer a stream
externP _read ; write to file handle
sBegin code
assumes cs,code
assumes ds,data
;***
;int _filbuf(stream) - fill buffer and get first character
;
;Purpose:
; get a buffer if the file doesn't have one, read into it, return first char.
; try to get a buffer, if a user buffer is not assigned. intended to be
; called by the user only thru the getc macro. assume no input stream is to
; remain unbuffered when memory is available unless it is marked _IONBF. at
; worst, give it a single char buffer. the need for a buffer, no matter how
; small, becomes evident when we consider the ungetc's necessary in scanf
;
; [NOTE 1: Multi-thread - _filbuf() assumes that the caller has aquired
; the stream lock, if needed.]
;
; [NOTE 2: The code depends on _iob[] and _iob2[] being near arrays of the
; total size and element size.]
;
; [NOTE 3: The use of _IOCTRLZ is tied closely to ftell() and also to
; lowio read()'s FEOFLAG flag.]
;
;Entry:
; FILE *stream - stream to read from
;
;Exit:
; returns first character from buffer (next character to be read)
; returns EOF if the FILE is actually a string, or not open for reading, or
; if open for writing or if no more chars to read.
; all fields in FILE structure may be changed except _file.
;
;Exceptions:
;
;*******************************************************************************
cProc _filbuf,
parmDP stream
cBegin
mov si,word ptr [stream] ; set si = stream = _iob entry
mov al,[si]._flag ; set al = stream->_flag
;**
; Check that stream is in use, and neither _IOSTRG nor _IOWRT
; is set.
test al,(_IOREAD OR _IORW OR _IOWRT) ; stream in use?
jz reteof ; no, error
test al,_IOSTRG ; is it a string iob?
jnz reteof ; yup, error
test al,_IOWRT ; write only file?
jnz seterr1 ; yup, error
;**
; Set:
; set _IOREAD (in stream->_flag)
; di = _iob2 entry (i.e., stream2 pointer)
or al,_IOREAD
mov [si]._flag,al
mov di,si
sub di,dataOFFSET _iob
add di,dataOFFSET _iob2
test al,_IOMYBUF OR _IONBF
jnz doread
test [di]._flag2,_IOYOURBUF
jnz doread
;**
; No buffer, try to get one.
if sizeD
push ds ; push arg
push si
else
push si ; push arg
endif
call _getbuf ; _getbuf(stream)
if sizeD
add sp,4 ; clean off arg
else
pop ax ; clean off arg
endif
; fall thru
;**
; Call lowio's read() to fill the buffer. Note that if the stream/handle
; is in text mode, the number of bytes read may well be less than _bufsiz.
doread:
mov ax,word ptr [si]._base ; set _ptr equal to _base (note: even
mov word ptr [si]._ptr,ax ; in large model, only need to change
; the offset portino of _ptr)
push [di]._bufsiz ; push args
if sizeD
push word ptr [si]._base + 2
push ax
else
push ax
endif
xor bx,bx
mov bl,[si]._file ; bl=_file / bh=0 (for later)
push bx
callcrt _read ; _read(_file, _base, _bufsiz)
if sizeD
add sp,8 ; clean off stack
else
add sp,6 ; clean off stack
endif
or ax,ax ; 0 bytes read?
jz seteof ; yes, we've hit eof
cmp ax,-1 ; did an error occur?
jne read_ok ; no, continue with good read code
;fall through to seterr2 ; yes, go set _flag and ret value
;**
; --- Error handling code ---
; (located in the middle of the source so all paths can get to it)
;
seterr2:
or [si]._flag,_IOERR
jmp short zerocnt
seterr1:
or [si]._flag,_IOERR
jmp short reteof
seteof:
or [si]._flag,_IOEOF
; fall thru
zerocnt:
mov [si]._cnt,0
; fall thru
reteof:
mov ax,EOF
jmp short done ; return the error
;**
;**
; The call to read() was successful.
;**
; If the file is read-only, text mode, and we hit a ^Z char, set _IOCTRLZ flag.
; ax = read count
; bl=stream->_file
; bh=0
read_ok:
mov bh,byte ptr [bx + dataOFFSET _osfile] ; bh =_osfile[fd]
and bh,(FTEXT OR FEOFLAG) ; get lowio text mode and ^Z bits
cmp bh,(FTEXT OR FEOFLAG) ; are they both on ??
jne end_ctrlz ; if not, jump out
mov bh,[si]._flag ; bh = stream->_flag
test bh,(_IORW OR _IOWRT) ; is file read-only ??
jnz end_ctrlz ; if not, jump out
or [di]._flag2,_IOCTRLZ ; flip ^Z flag on
end_ctrlz:
;**
; Get the first char out of the stream buffer (to be the return value).
; ax = read count
dec ax
mov [si]._cnt,ax
if sizeD
les bx,[si]._ptr
xor ax,ax
mov al,byte ptr es:[bx]
else
mov bx,[si]._ptr
xor ax,ax
mov al,byte ptr [bx]
endif
inc bx
mov word ptr [si]._ptr,bx
done:
cEnd
sEnd code
end
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