--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/miscellany/less-177/input.c	Mon Apr 18 23:46:02 2005 +0900
@@ -0,0 +1,261 @@
+/*
+ * High level routines dealing with getting lines of input 
+ * from the file being viewed.
+ *
+ * When we speak of "lines" here, we mean PRINTABLE lines;
+ * lines processed with respect to the screen width.
+ * We use the term "raw line" to refer to lines simply
+ * delimited by newlines; not processed with respect to screen width.
+ */
+
+#include "less.h"
+
+extern int squeeze;
+extern int chopline;
+extern int sigs;
+
+/*
+ * Get the next line.
+ * A "current" position is passed and a "new" position is returned.
+ * The current position is the position of the first character of
+ * a line.  The new position is the position of the first character
+ * of the NEXT line.  The line obtained is the line starting at curr_pos.
+ */
+	public POSITION
+forw_line(curr_pos)
+	POSITION curr_pos;
+{
+	POSITION new_pos;
+	register int c;
+	int blankline;
+	int endline;
+
+	if (curr_pos == NULL_POSITION || ch_seek(curr_pos))
+	{
+		null_line();
+		return (NULL_POSITION);
+	}
+
+	prewind();
+	plinenum(curr_pos);
+	(void) ch_seek(curr_pos);
+
+	c = ch_forw_get();
+	if (c == EOI)
+	{
+		null_line();
+		return (NULL_POSITION);
+	}
+	blankline = (c == '\n' || c == '\r');
+
+	for (;;)
+	{
+		if (sigs)
+		{
+			null_line();
+			return (NULL_POSITION);
+		}
+		if (c == '\n' || c == EOI)
+		{
+			/*
+			 * End of the line.
+			 */
+			new_pos = ch_tell();
+			endline = 1;
+			break;
+		}
+
+		/*
+		 * Append the char to the line and get the next char.
+		 */
+		if (pappend(c))
+		{
+			/*
+			 * The char won't fit in the line; the line
+			 * is too long to print in the screen width.
+			 * End the line here.
+			 */
+			if (chopline)
+			{
+				do
+				{
+					c = ch_forw_get();
+				} while (c != '\n' && c != EOI);
+				new_pos = ch_tell();
+				endline = 1;
+			} else
+			{
+				new_pos = ch_tell() - 1;
+				endline = 0;
+			}
+			break;
+		}
+		c = ch_forw_get();
+	}
+	pdone(endline);
+
+	if (squeeze && blankline)
+	{
+		/*
+		 * This line is blank.
+		 * Skip down to the last contiguous blank line
+		 * and pretend it is the one which we are returning.
+		 */
+		while ((c = ch_forw_get()) == '\n' || c == '\r')
+			if (sigs)
+			{
+				null_line();
+				return (NULL_POSITION);
+			}
+		if (c != EOI)
+			(void) ch_back_get();
+		new_pos = ch_tell();
+	}
+
+	return (new_pos);
+}
+
+/*
+ * Get the previous line.
+ * A "current" position is passed and a "new" position is returned.
+ * The current position is the position of the first character of
+ * a line.  The new position is the position of the first character
+ * of the PREVIOUS line.  The line obtained is the one starting at new_pos.
+ */
+	public POSITION
+back_line(curr_pos)
+	POSITION curr_pos;
+{
+	POSITION new_pos, begin_new_pos;
+	int c;
+	int endline;
+
+	if (curr_pos == NULL_POSITION || curr_pos <= ch_zero() ||
+		ch_seek(curr_pos-1))
+	{
+		null_line();
+		return (NULL_POSITION);
+	}
+
+	if (squeeze)
+	{
+		/*
+		 * Find out if the "current" line was blank.
+		 */
+		(void) ch_forw_get();	/* Skip the newline */
+		c = ch_forw_get();	/* First char of "current" line */
+		(void) ch_back_get();	/* Restore our position */
+		(void) ch_back_get();
+
+		if (c == '\n')
+		{
+			/*
+			 * The "current" line was blank.
+			 * Skip over any preceding blank lines,
+			 * since we skipped them in forw_line().
+			 */
+			while ((c = ch_back_get()) == '\n' || c == '\r')
+				if (sigs)
+				{
+					null_line();
+					return (NULL_POSITION);
+				}
+			if (c == EOI)
+			{
+				null_line();
+				return (NULL_POSITION);
+			}
+			(void) ch_forw_get();
+		}
+	}
+
+	/*
+	 * Scan backwards until we hit the beginning of the line.
+	 */
+	for (;;)
+	{
+		if (sigs)
+		{
+			null_line();
+			return (NULL_POSITION);
+		}
+		c = ch_back_get();
+		if (c == '\n')
+		{
+			/*
+			 * This is the newline ending the previous line.
+			 * We have hit the beginning of the line.
+			 */
+			new_pos = ch_tell() + 1;
+			break;
+		}
+		if (c == EOI)
+		{
+			/*
+			 * We have hit the beginning of the file.
+			 * This must be the first line in the file.
+			 * This must, of course, be the beginning of the line.
+			 */
+			new_pos = ch_tell();
+			break;
+		}
+	}
+
+	/*
+	 * Now scan forwards from the beginning of this line.
+	 * We keep discarding "printable lines" (based on screen width)
+	 * until we reach the curr_pos.
+	 *
+	 * {{ This algorithm is pretty inefficient if the lines
+	 *    are much longer than the screen width, 
+	 *    but I don't know of any better way. }}
+	 */
+	if (ch_seek(new_pos))
+	{
+		null_line();
+		return (NULL_POSITION);
+	}
+	endline = 0;
+    loop:
+	begin_new_pos = new_pos;
+	prewind();
+	plinenum(new_pos);
+	(void) ch_seek(new_pos);
+
+	do
+	{
+		c = ch_forw_get();
+		if (c == EOI || sigs)
+		{
+			null_line();
+			return (NULL_POSITION);
+		}
+		new_pos++;
+		if (c == '\n')
+		{
+			endline = 1;
+			break;
+		}
+		if (pappend(c))
+		{
+			/*
+			 * Got a full printable line, but we haven't
+			 * reached our curr_pos yet.  Discard the line
+			 * and start a new one.
+			 */
+			if (chopline)
+			{
+				endline = 1;
+				break;
+			}
+			pdone(0);
+			(void) ch_back_get();
+			new_pos--;
+			goto loop;
+		}
+	} while (new_pos < curr_pos);
+
+	pdone(endline);
+
+	return (begin_new_pos);
+}