1/*	$NetBSD: position.c,v 1.2 2011/07/03 19:51:26 tron Exp $	*/
2
3/*
4 * Copyright (C) 1984-2011  Mark Nudelman
5 *
6 * You may distribute under the terms of either the GNU General Public
7 * License or the Less License, as specified in the README file.
8 *
9 * For more information about less, or for information on how to
10 * contact the author, see the README file.
11 */
12
13
14/*
15 * Routines dealing with the "position" table.
16 * This is a table which tells the position (in the input file) of the
17 * first char on each currently displayed line.
18 *
19 * {{ The position table is scrolled by moving all the entries.
20 *    Would be better to have a circular table
21 *    and just change a couple of pointers. }}
22 */
23
24#include "less.h"
25#include "position.h"
26
27static POSITION *table = NULL;	/* The position table */
28static int table_size;
29
30extern int sc_width, sc_height;
31
32/*
33 * Return the starting file position of a line displayed on the screen.
34 * The line may be specified as a line number relative to the top
35 * of the screen, but is usually one of these special cases:
36 *	the top (first) line on the screen
37 *	the second line on the screen
38 *	the bottom line on the screen
39 *	the line after the bottom line on the screen
40 */
41	public POSITION
42position(where)
43	int where;
44{
45	switch (where)
46	{
47	case BOTTOM:
48		where = sc_height - 2;
49		break;
50	case BOTTOM_PLUS_ONE:
51		where = sc_height - 1;
52		break;
53	case MIDDLE:
54		where = (sc_height - 1) / 2;
55	}
56	return (table[where]);
57}
58
59/*
60 * Add a new file position to the bottom of the position table.
61 */
62	public void
63add_forw_pos(pos)
64	POSITION pos;
65{
66	register int i;
67
68	/*
69	 * Scroll the position table up.
70	 */
71	for (i = 1;  i < sc_height;  i++)
72		table[i-1] = table[i];
73	table[sc_height - 1] = pos;
74}
75
76/*
77 * Add a new file position to the top of the position table.
78 */
79	public void
80add_back_pos(pos)
81	POSITION pos;
82{
83	register int i;
84
85	/*
86	 * Scroll the position table down.
87	 */
88	for (i = sc_height - 1;  i > 0;  i--)
89		table[i] = table[i-1];
90	table[0] = pos;
91}
92
93/*
94 * Initialize the position table, done whenever we clear the screen.
95 */
96	public void
97pos_clear()
98{
99	register int i;
100
101	for (i = 0;  i < sc_height;  i++)
102		table[i] = NULL_POSITION;
103}
104
105/*
106 * Allocate or reallocate the position table.
107 */
108	public void
109pos_init()
110{
111	struct scrpos scrpos;
112	scrpos.pos = scrpos.ln = 0;	/* XXX: GCC */
113
114	if (sc_height <= table_size)
115		return;
116	/*
117	 * If we already have a table, remember the first line in it
118	 * before we free it, so we can copy that line to the new table.
119	 */
120	if (table != NULL)
121	{
122		get_scrpos(&scrpos);
123		free((char*)table);
124	} else
125		scrpos.pos = NULL_POSITION;
126	table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
127	table_size = sc_height;
128	pos_clear();
129	if (scrpos.pos != NULL_POSITION)
130		table[scrpos.ln-1] = scrpos.pos;
131}
132
133/*
134 * See if the byte at a specified position is currently on the screen.
135 * Check the position table to see if the position falls within its range.
136 * Return the position table entry if found, -1 if not.
137 */
138	public int
139onscreen(pos)
140	POSITION pos;
141{
142	register int i;
143
144	if (pos < table[0])
145		return (-1);
146	for (i = 1;  i < sc_height;  i++)
147		if (pos < table[i])
148			return (i-1);
149	return (-1);
150}
151
152/*
153 * See if the entire screen is empty.
154 */
155	public int
156empty_screen()
157{
158	return (empty_lines(0, sc_height-1));
159}
160
161	public int
162empty_lines(s, e)
163	int s;
164	int e;
165{
166	register int i;
167
168	for (i = s;  i <= e;  i++)
169		if (table[i] != NULL_POSITION)
170			return (0);
171	return (1);
172}
173
174/*
175 * Get the current screen position.
176 * The screen position consists of both a file position and
177 * a screen line number where the file position is placed on the screen.
178 * Normally the screen line number is 0, but if we are positioned
179 * such that the top few lines are empty, we may have to set
180 * the screen line to a number > 0.
181 */
182	public void
183get_scrpos(scrpos)
184	struct scrpos *scrpos;
185{
186	register int i;
187
188	/*
189	 * Find the first line on the screen which has something on it,
190	 * and return the screen line number and the file position.
191	 */
192	for (i = 0; i < sc_height;  i++)
193		if (table[i] != NULL_POSITION)
194		{
195			scrpos->ln = i+1;
196			scrpos->pos = table[i];
197			return;
198		}
199	/*
200	 * The screen is empty.
201	 */
202	scrpos->pos = NULL_POSITION;
203}
204
205/*
206 * Adjust a screen line number to be a simple positive integer
207 * in the range { 0 .. sc_height-2 }.
208 * (The bottom line, sc_height-1, is reserved for prompts, etc.)
209 * The given "sline" may be in the range { 1 .. sc_height-1 }
210 * to refer to lines relative to the top of the screen (starting from 1),
211 * or it may be in { -1 .. -(sc_height-1) } to refer to lines
212 * relative to the bottom of the screen.
213 */
214	public int
215adjsline(sline)
216	int sline;
217{
218	/*
219	 * Negative screen line number means
220	 * relative to the bottom of the screen.
221	 */
222	if (sline < 0)
223		sline += sc_height;
224	/*
225	 * Can't be less than 1 or greater than sc_height-1.
226	 */
227	if (sline <= 0)
228		sline = 1;
229	if (sline >= sc_height)
230		sline = sc_height - 1;
231	/*
232	 * Return zero-based line number, not one-based.
233	 */
234	return (sline-1);
235}
236