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/*
* Low level character input from the input file.
* We use these special purpose routines which optimize moving
* both forward and backward from the current read pointer.
*/
#include "less.h"
public int file = -1; /* File descriptor of the input file */
/*
* Pool of buffers holding the most recently used blocks of the input file.
*/
#define BUFSIZ 1024
struct buf {
struct buf *next, *prev;
long block;
int datasize;
char data[BUFSIZ];
};
public int nbufs;
/*
* The buffer pool is kept as a doubly-linked circular list,
* in order from most- to least-recently used.
* The circular list is anchored by buf_anchor.
*/
#define END_OF_CHAIN ((struct buf *)&buf_anchor)
#define buf_head buf_anchor.next
#define buf_tail buf_anchor.prev
static struct {
struct buf *next, *prev;
} buf_anchor = { END_OF_CHAIN, END_OF_CHAIN };
extern int clean_data;
extern int ispipe;
extern int autobuf;
extern int cbufs;
extern int sigs;
#if LOGFILE
extern int logfile;
#endif
/*
* Current position in file.
* Stored as a block number and an offset into the block.
*/
static long ch_block;
static int ch_offset;
/*
* Length of file, needed if input is a pipe.
*/
static POSITION ch_fsize;
/*
* Number of bytes read, if input is standard input (a pipe).
*/
static POSITION last_piped_pos;
/*
* Get the character pointed to by the read pointer.
* ch_get() is a macro which is more efficient to call
* than fch_get (the function), in the usual case
* that the block desired is at the head of the chain.
*/
#define ch_get() ((buf_head->block == ch_block && \
ch_offset < buf_head->datasize) ? \
buf_head->data[ch_offset] : fch_get())
static int
fch_get()
{
register struct buf *bp;
register int n;
register char *p;
POSITION pos;
/*
* Look for a buffer holding the desired block.
*/
for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next)
if (bp->block == ch_block)
{
if (ch_offset >= bp->datasize)
/*
* Need more data in this buffer.
*/
goto read_more;
/*
* On a pipe, we don't sort the buffers LRU
* because this can cause gaps in the buffers.
* For example, suppose we've got 12 1K buffers,
* and a 15K input stream. If we read the first 12K
* sequentially, then jump to line 1, then jump to
* the end, the buffers have blocks 0,4,5,6,..,14.
* If we then jump to line 1 again and try to
* read sequentially, we're out of luck when we
* get to block 1 (we'd get the "pipe error" below).
* To avoid this, we only sort buffers on a pipe
* when we actually READ the data, not when we
* find it already buffered.
*/
if (ispipe)
return (bp->data[ch_offset]);
goto found;
}
/*
* Block is not in a buffer.
* Take the least recently used buffer
* and read the desired block into it.
* If the LRU buffer has data in it,
* and autobuf is true, and input is a pipe,
* then try to allocate a new buffer first.
*/
if (autobuf && ispipe && buf_tail->block != (long)(-1))
(void) ch_addbuf(1);
bp = buf_tail;
bp->block = ch_block;
bp->datasize = 0;
read_more:
pos = (ch_block * BUFSIZ) + bp->datasize;
if (ispipe)
{
/*
* The data requested should be immediately after
* the last data read from the pipe.
*/
if (pos != last_piped_pos)
{
error("pipe error");
quit();
}
} else
lseek(file, pos, 0);
/*
* Read the block.
* If we read less than a full block, we just return the
* partial block and pick up the rest next time.
*/
n = iread(file, &bp->data[bp->datasize], BUFSIZ - bp->datasize);
if (n == READ_INTR)
return (EOI);
if (n < 0)
{
error("read error");
quit();
}
if (ispipe)
last_piped_pos += n;
#if LOGFILE
/*
* If we have a log file, write the new data to it.
*/
if (logfile >= 0 && n > 0)
write(logfile, &bp->data[bp->datasize], n);
#endif
bp->datasize += n;
/*
* Set an EOI marker in the buffered data itself.
* Then ensure the data is "clean": there are no
* extra EOI chars in the data and that the "meta"
* bit (the 0200 bit) is reset in each char.
*/
if (n == 0)
{
ch_fsize = pos;
bp->data[bp->datasize++] = EOI;
}
if (!clean_data)
{
p = &bp->data[bp->datasize];
while (--n >= 0)
{
*--p &= 0177;
if (*p == EOI)
*p = '@';
}
}
found:
if (buf_head != bp)
{
/*
* Move the buffer to the head of the buffer chain.
* This orders the buffer chain, most- to least-recently used.
*/
bp->next->prev = bp->prev;
bp->prev->next = bp->next;
bp->next = buf_head;
bp->prev = END_OF_CHAIN;
buf_head->prev = bp;
buf_head = bp;
}
if (ch_offset >= bp->datasize)
/*
* After all that, we still don't have enough data.
* Go back and try again.
*/
goto read_more;
return (bp->data[ch_offset]);
}
#if LOGFILE
/*
* Close the logfile.
* If we haven't read all of standard input into it, do that now.
*/
public void
end_logfile()
{
static int tried = 0;
if (logfile < 0)
return;
if (!tried && ch_fsize == NULL_POSITION)
{
tried = 1;
ierror("finishing logfile");
while (ch_forw_get() != EOI)
if (sigs)
break;
}
close(logfile);
logfile = -1;
}
/*
* Start a log file AFTER less has already been running.
* Invoked from the - command; see toggle_option().
* Write all the existing buffered data to the log file.
*/
public void
sync_logfile()
{
register struct buf *bp;
register int n;
long block;
long last_block;
last_block = (last_piped_pos + BUFSIZ - 1) / BUFSIZ;
for (block = 0; block <= last_block; block++)
for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next)
if (bp->block == block)
{
n = bp->datasize;
if (bp->data[n-1] == EOI)
n--;
write(logfile, bp->data, n);
break;
}
}
#endif
/*
* Determine if a specific block is currently in one of the buffers.
*/
static int
buffered(block)
long block;
{
register struct buf *bp;
for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next)
if (bp->block == block)
return (1);
return (0);
}
/*
* Seek to a specified position in the file.
* Return 0 if successful, non-zero if can't seek there.
*/
public int
ch_seek(pos)
register POSITION pos;
{
long new_block;
new_block = pos / BUFSIZ;
if (!ispipe || pos == last_piped_pos || buffered(new_block))
{
/*
* Set read pointer.
*/
ch_block = new_block;
ch_offset = pos % BUFSIZ;
return (0);
}
return (1);
}
/*
* Seek to the end of the file.
*/
public int
ch_end_seek()
{
if (!ispipe)
return (ch_seek(ch_length()));
/*
* Do it the slow way: read till end of data.
*/
while (ch_forw_get() != EOI)
if (sigs)
return (1);
return (0);
}
/*
* Seek to the beginning of the file, or as close to it as we can get.
* We may not be able to seek there if input is a pipe and the
* beginning of the pipe is no longer buffered.
*/
public int
ch_beg_seek()
{
register struct buf *bp, *firstbp;
/*
* Try a plain ch_seek first.
*/
if (ch_seek((POSITION)0) == 0)
return (0);
/*
* Can't get to position 0.
* Look thru the buffers for the one closest to position 0.
*/
firstbp = bp = buf_head;
if (bp == END_OF_CHAIN)
return (1);
while ((bp = bp->next) != END_OF_CHAIN)
if (bp->block < firstbp->block)
firstbp = bp;
ch_block = firstbp->block;
ch_offset = 0;
return (0);
}
/*
* Return the length of the file, if known.
*/
public POSITION
ch_length()
{
if (ispipe)
return (ch_fsize);
return ((POSITION)(lseek(file, (offset_t)0, 2)));
}
/*
* Return the current position in the file.
*/
public POSITION
ch_tell()
{
return (ch_block * BUFSIZ + ch_offset);
}
/*
* Get the current char and post-increment the read pointer.
*/
public int
ch_forw_get()
{
register int c;
c = ch_get();
if (c != EOI && ++ch_offset >= BUFSIZ)
{
ch_offset = 0;
ch_block ++;
}
return (c);
}
/*
* Pre-decrement the read pointer and get the new current char.
*/
public int
ch_back_get()
{
if (--ch_offset < 0)
{
if (ch_block <= 0 || (ispipe && !buffered(ch_block-1)))
{
ch_offset = 0;
return (EOI);
}
ch_offset = BUFSIZ - 1;
ch_block--;
}
return (ch_get());
}
/*
* Allocate buffers.
* Caller wants us to have a total of at least want_nbufs buffers.
* keep==1 means keep the data in the current buffers;
* otherwise discard the old data.
*/
public void
ch_init(want_nbufs, keep)
int want_nbufs;
int keep;
{
register struct buf *bp;
char message[80];
cbufs = nbufs;
if (nbufs < want_nbufs && ch_addbuf(want_nbufs - nbufs))
{
/*
* Cannot allocate enough buffers.
* If we don't have ANY, then quit.
* Otherwise, just report the error and return.
*/
sprintf(message, "cannot allocate %d buffers",
want_nbufs - nbufs);
error(message);
if (nbufs == 0)
quit();
return;
}
if (keep)
return;
/*
* We don't want to keep the old data,
* so initialize all the buffers now.
*/
for (bp = buf_head; bp != END_OF_CHAIN; bp = bp->next)
bp->block = (long)(-1);
last_piped_pos = (POSITION)0;
ch_fsize = NULL_POSITION;
(void) ch_seek((POSITION)0);
}
/*
* Allocate some new buffers.
* The buffers are added to the tail of the buffer chain.
*/
static int
ch_addbuf(nnew)
int nnew;
{
register struct buf *bp;
register struct buf *newbufs;
/*
* We don't have enough buffers.
* Allocate some new ones.
*/
newbufs = (struct buf *) calloc(nnew, sizeof(struct buf));
if (newbufs == NULL)
return (1);
/*
* Initialize the new buffers and link them together.
* Link them all onto the tail of the buffer list.
*/
nbufs += nnew;
cbufs = nbufs;
for (bp = &newbufs[0]; bp < &newbufs[nnew]; bp++)
{
bp->next = bp + 1;
bp->prev = bp - 1;
bp->block = (long)(-1);
}
newbufs[nnew-1].next = END_OF_CHAIN;
newbufs[0].prev = buf_tail;
buf_tail->next = &newbufs[0];
buf_tail = &newbufs[nnew-1];
return (0);
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.