--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/miscellany/less-177/ch.c	Mon Apr 18 23:46:02 2005 +0900
@@ -0,0 +1,567 @@
+/*
+ * 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 */
+public int ignore_eoi;
+
+/*
+ * Pool of buffers holding the most recently used blocks of the input file.
+ */
+#define BUFSIZ	1024
+struct buf {
+	struct buf *next, *prev;  /* Must be first to match struct filestate */
+	long block;
+	unsigned int datasize;
+	unsigned char data[BUFSIZ];
+};
+
+/*
+ * 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 the file state "thisfile".
+ *
+ * The file state is maintained in a filestate structure.
+ * There are two such structures, one used when input is a pipe
+ * and the other when input is an ordinary file.
+ * This is so that we can leave a pipe, look and other files,
+ * and return to the pipe without losing buffered data.
+ * Buffered data can be reconstructed for a non-pipe file by
+ * simply re-reading the file, but a pipe cannot be re-read.
+ */
+
+struct filestate {
+	struct buf *next, *prev;   /* Must be first to match struct buf */
+	POSITION fpos;
+	int nbufs;
+	long block;
+	int offset;
+	POSITION fsize;
+};
+
+#define	END_OF_CHAIN	((struct buf *)thisfile)
+#define	buf_head	thisfile->next
+#define	buf_tail	thisfile->prev
+#define	ch_nbufs	thisfile->nbufs
+#define	ch_block	thisfile->block
+#define	ch_offset	thisfile->offset
+#define	ch_fpos		thisfile->fpos
+#define	ch_fsize	thisfile->fsize
+
+static struct filestate pipefile =
+	{ (struct buf *)&pipefile, (struct buf *)&pipefile };
+
+static struct filestate nonpipefile = 
+	{ (struct buf *)&nonpipefile, (struct buf *)&nonpipefile };
+
+static struct filestate *thisfile;
+
+extern int ispipe;
+extern int autobuf;
+extern int sigs;
+#if LOGFILE
+extern int logfile;
+extern char *namelogfile;
+#endif
+
+static int ch_addbuf();
+
+
+/*
+ * 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()   ((ch_block == buf_head->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 int slept;
+	POSITION pos;
+	POSITION len;
+
+	slept = 0;
+
+	/*
+	 * 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;
+			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))
+		if (ch_addbuf(1))
+			/*
+			 * Allocation failed: turn off autobuf.
+			 */
+			autobuf = 0;
+	bp = buf_tail;
+	bp->block = ch_block;
+	bp->datasize = 0;
+
+    read_more:
+	pos = (ch_block * BUFSIZ) + bp->datasize;
+	if ((len = ch_length()) != NULL_POSITION && pos >= len)
+		/*
+		 * At end of file.
+		 */
+		return (EOI);
+
+	if (pos != ch_fpos)
+	{
+		/*
+		 * Not at the correct position: must seek.
+		 * If input is a pipe, we're in trouble (can't seek on a pipe).
+		 * Some data has been lost: just return "?".
+		 */
+		if (ispipe)
+			return ('?');
+		if (lseek(file, (offset_t)pos, 0) == BAD_LSEEK)
+		{
+ 			error("seek error", NULL_PARG);
+ 			quit(1);
+ 		}
+ 		ch_fpos = pos;
+ 	}
+
+	/*
+	 * Read the block.
+	 * If we read less than a full block, that's ok.
+	 * We use partial block and pick up the rest next time.
+	 */
+	n = iread(file, &bp->data[bp->datasize], 
+		(unsigned int)(BUFSIZ - bp->datasize));
+	if (n == READ_INTR)
+		return (EOI);
+	if (n < 0)
+	{
+		error("read error", NULL_PARG);
+		quit(1);
+	}
+	ch_fpos += n;
+
+#if LOGFILE
+	/*
+	 * If we have a log file, write the new data to it.
+	 */
+	if (logfile >= 0 && n > 0)
+		write(logfile, (char *) &bp->data[bp->datasize], n);
+#endif
+
+	bp->datasize += n;
+
+	/*
+	 * If we have read to end of file, set ch_fsize to indicate
+	 * the position of the end of file.
+	 */
+	if (n == 0)
+	{
+		ch_fsize = pos;
+		if (ignore_eoi)
+		{
+			/*
+			 * We are ignoring EOF.
+			 * Wait a while, then try again.
+			 */
+			if (!slept)
+				ierror("Waiting for data", NULL_PARG);
+			sleep(1);
+			slept = 1;
+		}
+		if (sigs)
+			return (EOI);
+	}
+
+    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", NULL_PARG);
+		while (ch_forw_get() != EOI)
+			if (sigs)
+				break;
+	}
+	close(logfile);
+	logfile = -1;
+	namelogfile = NULL;
+}
+
+/*
+ * 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;
+	long block;
+	long last_block;
+
+	last_block = (ch_fpos + 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)
+			{
+				write(logfile, (char *) bp->data, bp->datasize);
+				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;
+	POSITION len;
+
+	len = ch_length();
+	if (pos < ch_zero() || (len != NULL_POSITION && pos > len))
+		return (1);
+
+	new_block = pos / BUFSIZ;
+	if (ispipe && pos != ch_fpos && !buffered(new_block))
+		return (1);
+	/*
+	 * Set read pointer.
+	 */
+	ch_block = new_block;
+	ch_offset = pos % BUFSIZ;
+	return (0);
+}
+
+/*
+ * Seek to the end of the file.
+ */
+	public int
+ch_end_seek()
+{
+	POSITION len;
+
+	if (!ispipe)
+		ch_fsize = filesize(file);
+
+	len = ch_length();
+	if (len != NULL_POSITION)
+		return (ch_seek(len));
+
+	/*
+	 * 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(ch_zero()) == 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 (ignore_eoi)
+		return (NULL_POSITION);
+	return (ch_fsize);
+}
+
+/*
+ * Return the current position in the file.
+ */
+#define	tellpos(blk,off)   ((POSITION)((((long)(blk)) * BUFSIZ) + (off)))
+
+	public POSITION
+ch_tell()
+{
+	return (tellpos(ch_block, 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)
+		return (EOI);
+	if (ch_offset < BUFSIZ-1)
+		ch_offset++;
+	else
+	{
+#if __ZOFFSET /* NOT WORKING */
+		if (ch_fsize != NULL_POSITION && 
+		    tellpos(ch_block+1, 0) >= ch_fsize)
+			return (EOI);
+#endif
+		ch_block ++;
+		ch_offset = 0;
+	}
+	return (c);
+}
+
+/*
+ * Pre-decrement the read pointer and get the new current char.
+ */
+	public int
+ch_back_get()
+{
+	if (ch_offset > 0)
+		ch_offset --;
+	else
+	{
+#if __ZOFFSET /* NOT WORKING */
+		if (tellpos(ch_block-1, BUFSIZ-1) < ch_zero())
+			return (EOI);
+#else
+		if (ch_block <= 0)
+			return (EOI);
+#endif
+		if (ispipe && !buffered(ch_block-1))
+			return (EOI);
+		ch_block--;
+		ch_offset = BUFSIZ-1;
+	}
+	return (ch_get());
+}
+
+/*
+ * Allocate buffers.
+ * Caller wants us to have a total of at least want_nbufs buffers.
+ */
+	public int
+ch_nbuf(want_nbufs)
+	int want_nbufs;
+{
+	PARG parg;
+
+	if (ch_nbufs < want_nbufs && ch_addbuf(want_nbufs - ch_nbufs))
+	{
+		/*
+		 * Cannot allocate enough buffers.
+		 * If we don't have ANY, then quit.
+		 * Otherwise, just report the error and return.
+		 */
+		parg.p_int = want_nbufs - ch_nbufs;
+		error("Cannot allocate %d buffers", &parg);
+		if (ch_nbufs == 0)
+			quit(1);
+	}
+	return (ch_nbufs);
+}
+
+/*
+ * Flush any saved file state, including buffer contents.
+ */
+	public void
+ch_flush()
+{
+	register struct buf *bp;
+
+	if (ispipe)
+	{
+		/*
+		 * If input is a pipe, we don't flush buffer contents,
+		 * since the contents can't be recovered.
+		 */
+		ch_fsize = NULL_POSITION;
+		return;
+	}
+
+	/*
+	 * Initialize all the buffers.
+	 */
+	for (bp = buf_head;  bp != END_OF_CHAIN;  bp = bp->next)
+		bp->block = (long)(-1);
+
+	/*
+	 * Figure out the size of the file, if we can.
+	 */
+	ch_fsize = filesize(file);
+
+	/*
+	 * Seek to a known position: the beginning of the file.
+	 */
+	ch_fpos = 0;
+	ch_block = ch_fpos / BUFSIZ;
+	ch_offset = ch_fpos % BUFSIZ;
+
+	if (lseek(file, (offset_t)0, 0) == BAD_LSEEK)
+	{
+		/*
+		 * Warning only; even if the seek fails for some reason,
+		 * there's a good chance we're at the beginning anyway.
+		 * {{ I think this is bogus reasoning. }}
+		 */
+		error("seek error to 0", NULL_PARG);
+	}
+}
+
+/*
+ * 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.
+	 */
+	ch_nbufs += nnew;
+	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);
+}
+
+/*
+ * Use the pipe file state.
+ */
+	public void
+ch_pipe()
+{
+	thisfile = &pipefile;
+}
+
+/*
+ * Use the non-pipe file state.
+ */
+	public void
+ch_nonpipe()
+{
+	thisfile = &nonpipefile;
+}