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Revision 1.3, Thu Aug 7 10:30:45 2003 UTC (17 years, 2 months ago) by agc
Move UCB-licensed code from 4-clause to 3-clause licence. Patches provided by Joel Baker in PR 22309, verified by myself.
.\" $NetBSD: pxin3.n,v 1.3 2003/08/07 10:30:45 agc Exp $ .\" .\" Copyright (c) 1979 The Regents of the University of California. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)pxin3.n 5.2 (Berkeley) 4/17/91 .\" .if !\n(xx .so tmac.p .ta 8n 16n 24n .nr H1 2 .if n .ND .NH Input/output .NH 2 The files structure .PP Each file in the Pascal environment is represented by a pointer to a .I files structure in the heap. At the location addressed by the pointer is the element in the file's window variable. Behind this window variable is information about the file, at the following offsets: .so table3.1.n .PP Here .SM FBUF is a pointer to the system FILE block for the file. The standard system I/O library is used that provides block buffered input/output, with 1024 characters normally transferred at each read or write. .PP The files in the Pascal environment, are all linked together on a single file chain through the .SM FCHAIN links. For each file the .SM FLEV pointer gives its associated file variable. These are used to free files at block exit as described in section 3.3 below. .PP The FNAME and PFNAME give the associated file name for the file and the name to be used when printing error diagnostics respectively. Although these names are usually the same, .I input and .I output usually have no associated file name so the distinction is necessary. .PP The FUNIT word contains a set of flags. whose representations are: .TS center; l l l. EOF 0x0100 At end-of-file EOLN 0x0200 At end-of-line (text files only) SYNC 0x0400 File window is out of sync TEMP 0x0800 File is temporary FREAD 0x1000 File is open for reading FWRITE 0x2000 File is open for writing FTEXT 0x4000 File is a text file; process EOLN FDEF 0x8000 File structure created, but file not opened .TE .PP The EOF and EOLN bits here reflect the associated built-in function values. TEMP specifies that the file has a generated temporary name and that it should therefore be removed when its block exits. FREAD and FWRITE specify that .I reset and .I rewrite respectively have been done on the file so that input or output operations can be done. FTEXT specifies the file is a text file so that EOLN processing should be done, with newline characters turned into blanks, etc. .PP The SYNC bit, when true, specifies that there is no usable image in the file buffer window. As discussed in the .I "Berkeley Pascal User's Manual," the interactive environment necessitates having ``input^'' undefined at the beginning of execution so that a program may print a prompt before the user is required to type input. The SYNC bit implements this. When it is set, it specifies that the element in the window must be updated before it can be used. This is never done until necessary. .NH 2 Initialization of files .PP All the variables in the Pascal runtime environment are cleared to zero on block entry. This is necessary for simple processing of files. If a file is unused, its pointer will be .B nil. All references to an inactive file are thus references through a .B nil pointer. If the Pascal system did not clear storage to zero before execution it would not be possible to detect inactive files in this simple way; it would probably be necessary to generate (possibly complicated) code to initialize each file on block entry. .PP When a file is first mentioned in a .I reset or .I rewrite call, a buffer of the form described above is associated with it, and the necessary information about the file is placed in this buffer. The file is also linked into the active file chain. This chain is kept sorted by block mark address, the FLEV entries. .NH 2 Block exit .PP When block exit occurs the interpreter must free the files that are in use in the block and their associated buffers. This is simple and efficient because the files in the active file chain are sorted by increasing block mark address. This means that the files for the current block will be at the front of the chain. For each file that is no longer accessible the interpreter first flushes the files buffer if it is an output file. The interpreter then returns the file buffer and the files structure and window to the free space in the heap and removes the file from the active file chain. .NH 2 Flushing .PP Flushing all the file buffers at abnormal termination, or on a call to the procedure .I flush or .I message is done by flushing each file on the file chain that has the FWRITE bit set in its flags word. .NH 2 The active file .PP For input-output, .I px maintains a notion of an active file. Each operation that references a file makes the file it will be using the active file and then does its operation. A subtle point here is that one may do a procedure call to .I write that involves a call to a function that references another file, thereby destroying the active file set up before the .I write. Thus the active file is saved at block entry in the block mark and restored at block exit.\*(Dg .FS \*(dg\ It would probably be better to dispense with the notion of active file and use another mechanism that did not involve extra overhead on each procedure and function call. .FE .NH 2 File operations .PP Files in Pascal can be used in two distinct ways: as the object of .I read, .I write, .I get, and .I put calls, or indirectly as though they were pointers. The second use as pointers must be careful not to destroy the active file in a reference such as .LS write(output, input\(ua) .LE or the system would incorrectly write on the input device. .PP The fundamental operator related to the use of a file is .SM FNIL. This takes the file variable, as a pointer, insures that the pointer is not .B nil, and also that a usable image is in the file window, by forcing the .SM SYNC bit to be cleared. .PP A simple example that demonstrates the use of the file operators is given by .LS writeln(f) .LE that produces .DS .mD .TS lp-2w(8) l. RV:\fIl f\fP UNIT WRITLN .TE .DE .NH 2 Read operations .SH GET .IP Advance the active file to the next input element. .SH FNIL .IP A file pointer is on the stack. Insure that the associated file is active and that the file is synced so that there is input available in the window. .SH READ* .IP If the file is a text file, read a block of text and convert it to the internal type of the specified operand. If the file is not a text file then do an unformatted read of the next record. The procedure .SM READLN reads upto and including the next end of line character. .SH READE A .IP The operator .SM READE reads a string name of an enumerated type and converts it to its internal value. .SM READE takes a pointer to a data structure as shown in figure 3.2. .so fig3.2.n See the description of .SM NAM in the next section for an example. .NH 2 Write operations .SH PUT .IP Output the element in the active file window. .SH WRITEF s .IP The argument(s) on the stack are output by the .I fprintf standard .SM I/O library routine. The sub-opcode .I s specifies the number of longword arguments on the stack. .SH WRITEC .IP The character on the top of the stack is output without formatting. Formatted characters must be output with .SM WRITEF . .SH WRITES .IP The string specified by the pointer on the top of the stack is output by the .I fwrite standard .SM I/O library routine. All characters including nulls are printed. .SH WRITLN .IP A linefeed is output to the active file. The line-count for the file is incremented and checked against the line limit. .SH PAGE .IP A formfeed is output to the active file. .SH NAM A .IP The value on the top of the stack is converted to a pointer to an enumerated type string name. The address .SM A points to an enumerated type structure identical to that used by .SM READE . An error is raised if the value is out of range. The form of this structure for the predefined type .B boolean is shown in figure 3.3. .so fig3.3.n The code for .SM NAM is .DS .mD _NAM: \fBincl\fR lc \fBaddl3\fR (lc)+,ap,r6 #r6 points to scalar name list \fBmovl\fR (sp)+,r3 #r3 has data value \fBcmpw\fR r3,(r6)+ #check value out of bounds \fBbgequ\fR enamrng \fBmovzwl\fR (r6)[r3],r4 #r4 has string index \fBpushab\fR (r6)[r4] #push string pointer \fBjmp\fR (loop) enamrng: \fBmovw\fR $ENAMRNG,_perrno \fBjbr\fR error .DE The address of the table is calculated by adding the base address of the interpreter code, .I ap to the offset pointed to by .I lc . The first word of the table gives the number of records and provides a range check of the data to be output. The pointer is then calculated as .DS .mD tblbase = ap + A; size = *tblbase++; return(tblbase + tblbase[value]); .DE .SH MAX s,w .IP The sub-opcode .I s is subtracted from the integer on the top of the stack. The maximum of the result and the second argument, .I w , replaces the value on the top of the stack. This function verifies that variable specified width arguments are non-negative, and meet certain minimum width requirements. .SH MIN s .IP The minimum of the value on the top of the stack and the sub-opcode replaces the value on the top of the stack. .sp 1 .LP The uses of files and the file operations are summarized in an example which outputs a real variable (r) with a variable width field (i). .LS writeln('r =',r:i,' ',true); .LE that generates the code .DS .mD .TS lp-2w(8) l. UNITOUT FILE CON14:1 CON14:3 LVCON:4 "r =" WRITES RV8\fI:l r\fP RV4\fI:l i\fP MAX:8 1 RV4\fI:l i\fP MAX:1 1 LVCON:8 " %*.*E" FILE WRITEF:6 CONC4 \' \' WRITEC CON14:1 NAM \fIbool\fP LVCON:4 "%s" FILE WRITEF:3 WRITLN .TE .DE .PP Here the operator .SM UNITOUT is an abbreviated form of the operator .SM UNIT that is used when the file to be made active is .I output . A file descriptor, record count, string size, and a pointer to the constant string ``r ='' are pushed and then output by .SM WRITES . Next the value of .I r is pushed on the stack and the precision size is calculated by taking seven less than the width, but not less than one. This is followed by the width that is reduced by one to leave space for the required leading blank. If the width is too narrow, it is expanded by .I fprintf . A pointer to the format string is pushed followed by a file descriptor and the operator .SM WRITEF that prints out .I r . The value of six on .SM WRITEF comes from two longs for .I r and a long each for the precision, width, format string pointer, and file descriptor. The operator .SM CONC4 pushes the .I blank character onto a long on the stack that is then printed out by .SM WRITEC . The internal representation for .I true is pushed as a long onto the stack and is then replaced by a pointer to the string ``true'' by the operator .SM NAM using the table .I bool for conversion. This string is output by the operator .SM WRITEF using the format string ``%s''. Finally the operator .SM WRITLN appends a newline to the file. .NH 2 File activation and status operations .SH UNIT* .IP The file pointed to by the file pointer on the top of the stack is converted to be the active file. The opcodes .SM UNITINP and .SM UNITOUT imply standard input and output respectively instead of explicitly pushing their file pointers. .SH FILE .IP The standard .SM I/O library file descriptor associated with the active file is pushed onto the stack. .SH EOF .IP The file pointed to by the file pointer on the top of the stack is checked for end of file. A boolean is returned with .I true indicating the end of file condition. .SH EOLN .IP The file pointed to by the file pointer on the top of the stack is checked for end of line. A boolean is returned with .I true indicating the end of line condition. Note that only text files can check for end of line. .NH 2 File housekeeping operations .SH DEFNAME .IP Four data items are passed on the stack; the size of the data type associated with the file, the maximum size of the file name, a pointer to the file name, and a pointer to the file variable. A file record is created with the specified window size and the file variable set to point to it. The file is marked as defined but not opened. This allows .B program statement association of file names with file variables before their use by a .SM RESET or a .SM REWRITE . .SH BUFF s .IP The sub-opcode is placed in the external variable .I _bufopt to specify the amount of I/O buffering that is desired. The current options are: .DS 0 \- character at a time buffering 1 \- line at a time buffering 2 \- block buffering .DE The default value is 1. .SH RESET .br REWRITE .IP Four data items are passed on the stack; the size of the data type associated with the file, the maximum size of the name (possibly zero), a pointer to the file name (possibly null), and a pointer to the file variable. If the file has never existed it is created as in .SM DEFNAME . If no file name is specified and no previous name exists (for example one created by .SM DEFNAME ) then a system temporary name is created. .SM RESET then opens the file for input, while .SM REWRITE opens the file for output. .sp 1 .PP The three remaining file operations are .SM FLUSH that flushes the active file, .SM REMOVE that takes the pointer to a file name and removes the specified file, and .SM MESSAGE that flushes all the output files and sets the standard error file to be the active file.