Add less 643

third_party/less/position.c

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+/*
+ * Copyright (C) 1984-2023  Mark Nudelman
+ *
+ * You may distribute under the terms of either the GNU General Public
+ * License or the Less License, as specified in the README file.
+ *
+ * For more information, see the README file.
+ */
+
+
+/*
+ * Routines dealing with the "position" table.
+ * This is a table which tells the position (in the input file) of the
+ * first char on each currently displayed line.
+ *
+ * {{ The position table is scrolled by moving all the entries.
+ *    Would be better to have a circular table 
+ *    and just change a couple of pointers. }}
+ */
+
+#include "less.h"
+#include "position.h"
+
+static POSITION *table = NULL;  /* The position table */
+static int table_size = 0;
+
+extern int sc_width, sc_height;
+extern int header_lines;
+
+/*
+ * Return the starting file position of a line displayed on the screen.
+ * The line may be specified as a line number relative to the top
+ * of the screen, but is usually one of these special cases:
+ *      the top (first) line on the screen
+ *      the second line on the screen
+ *      the bottom line on the screen
+ *      the line after the bottom line on the screen
+ */
+public POSITION position(int sindex)
+{
+	switch (sindex)
+	{
+	case BOTTOM:
+		sindex = sc_height - 2;
+		break;
+	case BOTTOM_PLUS_ONE:
+		sindex = sc_height - 1;
+		break;
+	case MIDDLE:
+		sindex = (sc_height - 1) / 2;
+		break;
+	}
+	return (table[sindex]);
+}
+
+/*
+ * Add a new file position to the bottom of the position table.
+ */
+public void add_forw_pos(POSITION pos)
+{
+	int i;
+
+	/*
+	 * Scroll the position table up.
+	 */
+	for (i = 1;  i < sc_height;  i++)
+		table[i-1] = table[i];
+	table[sc_height - 1] = pos;
+}
+
+/*
+ * Add a new file position to the top of the position table.
+ */
+public void add_back_pos(POSITION pos)
+{
+	int i;
+
+	/*
+	 * Scroll the position table down.
+	 */
+	for (i = sc_height - 1;  i > 0;  i--)
+		table[i] = table[i-1];
+	table[0] = pos;
+}
+
+/*
+ * Initialize the position table, done whenever we clear the screen.
+ */
+public void pos_clear(void)
+{
+	int i;
+
+	for (i = 0;  i < sc_height;  i++)
+		table[i] = NULL_POSITION;
+}
+
+/*
+ * Allocate or reallocate the position table.
+ */
+public void pos_init(void)
+{
+	struct scrpos scrpos;
+
+	if (sc_height <= table_size)
+		return;
+	/*
+	 * If we already have a table, remember the first line in it
+	 * before we free it, so we can copy that line to the new table.
+	 */
+	if (table != NULL)
+	{
+		get_scrpos(&scrpos, TOP);
+		free((char*)table);
+	} else
+		scrpos.pos = NULL_POSITION;
+	table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
+	table_size = sc_height;
+	pos_clear();
+	if (scrpos.pos != NULL_POSITION)
+		table[scrpos.ln-1] = scrpos.pos;
+}
+
+/*
+ * See if the byte at a specified position is currently on the screen.
+ * Check the position table to see if the position falls within its range.
+ * Return the position table entry if found, -1 if not.
+ */
+public int onscreen(POSITION pos)
+{
+	int i;
+
+	if (pos < table[0])
+		return (-1);
+	for (i = 1;  i < sc_height;  i++)
+		if (pos < table[i])
+			return (i-1);
+	return (-1);
+}
+
+/*
+ * See if the entire screen is empty.
+ */
+public int empty_screen(void)
+{
+	return (empty_lines(0, sc_height-1));
+}
+
+public int empty_lines(int s, int e)
+{
+	int i;
+
+	for (i = s;  i <= e;  i++)
+		if (table[i] != NULL_POSITION && table[i] != 0)
+			return (0);
+	return (1);
+}
+
+/*
+ * Get the current screen position.
+ * The screen position consists of both a file position and
+ * a screen line number where the file position is placed on the screen.
+ * Normally the screen line number is 0, but if we are positioned
+ * such that the top few lines are empty, we may have to set
+ * the screen line to a number > 0.
+ */
+public void get_scrpos(struct scrpos *scrpos, int where)
+{
+	int i;
+	int dir;
+	int last;
+
+	switch (where)
+	{
+	case TOP:
+		i = 0; dir = +1; last = sc_height-2;
+		break;
+	case BOTTOM: case BOTTOM_PLUS_ONE:
+		i = sc_height-2; dir = -1; last = 0;
+		break;
+	default:
+		i = where;
+		if (table[i] == NULL_POSITION) {
+			scrpos->pos = NULL_POSITION;
+			return;
+		}
+		/* Values of dir and last don't matter after this. */
+		break;
+	}
+
+	/*
+	 * Find the first line on the screen which has something on it,
+	 * and return the screen line number and the file position.
+	 */
+	for (;; i += dir)
+	{
+		if (table[i] != NULL_POSITION)
+		{
+			scrpos->ln = i+1;
+			scrpos->pos = table[i];
+			return;
+		}
+		if (i == last) break;
+	}
+	/*
+	 * The screen is empty.
+	 */
+	scrpos->pos = NULL_POSITION;
+}
+
+/*
+ * Adjust a screen line number to be a simple positive integer
+ * in the range { 0 .. sc_height-2 }.
+ * (The bottom line, sc_height-1, is reserved for prompts, etc.)
+ * The given "sline" may be in the range { 1 .. sc_height-1 }
+ * to refer to lines relative to the top of the screen (starting from 1),
+ * or it may be in { -1 .. -(sc_height-1) } to refer to lines
+ * relative to the bottom of the screen.
+ */
+public int sindex_from_sline(int sline)
+{
+	/*
+	 * Negative screen line number means
+	 * relative to the bottom of the screen.
+	 */
+	if (sline < 0)
+		sline += sc_height;
+	/*
+	 * Can't be less than 1 or greater than sc_height.
+	 */
+	if (sline <= 0)
+		sline = 1;
+	if (sline > sc_height)
+		sline = sc_height;
+	/*
+	 * Return zero-based line number, not one-based.
+	 */
+	return (sline-1);
+}