1/*
2 * Copyright (C) 1984-2023  Mark Nudelman
3 *
4 * You may distribute under the terms of either the GNU General Public
5 * License or the Less License, as specified in the README file.
6 *
7 * For more information, see the README file.
8 */
9
10
11/*
12 * Routines dealing with the "position" table.
13 * This is a table which tells the position (in the input file) of the
14 * first char on each currently displayed line.
15 *
16 * {{ The position table is scrolled by moving all the entries.
17 *    Would be better to have a circular table
18 *    and just change a couple of pointers. }}
19 */
20
21#include "less.h"
22#include "position.h"
23
24static POSITION *table = NULL;  /* The position table */
25static int table_size = 0;
26
27extern int sc_width, sc_height;
28extern int header_lines;
29
30/*
31 * Return the starting file position of a line displayed on the screen.
32 * The line may be specified as a line number relative to the top
33 * of the screen, but is usually one of these special cases:
34 *      the top (first) line on the screen
35 *      the second line on the screen
36 *      the bottom line on the screen
37 *      the line after the bottom line on the screen
38 */
39public POSITION position(int sindex)
40{
41	switch (sindex)
42	{
43	case BOTTOM:
44		sindex = sc_height - 2;
45		break;
46	case BOTTOM_PLUS_ONE:
47		sindex = sc_height - 1;
48		break;
49	case MIDDLE:
50		sindex = (sc_height - 1) / 2;
51		break;
52	}
53	return (table[sindex]);
54}
55
56/*
57 * Add a new file position to the bottom of the position table.
58 */
59public void add_forw_pos(POSITION pos)
60{
61	int i;
62
63	/*
64	 * Scroll the position table up.
65	 */
66	for (i = 1;  i < sc_height;  i++)
67		table[i-1] = table[i];
68	table[sc_height - 1] = pos;
69}
70
71/*
72 * Add a new file position to the top of the position table.
73 */
74public void add_back_pos(POSITION pos)
75{
76	int i;
77
78	/*
79	 * Scroll the position table down.
80	 */
81	for (i = sc_height - 1;  i > 0;  i--)
82		table[i] = table[i-1];
83	table[0] = pos;
84}
85
86/*
87 * Initialize the position table, done whenever we clear the screen.
88 */
89public void pos_clear(void)
90{
91	int i;
92
93	for (i = 0;  i < sc_height;  i++)
94		table[i] = NULL_POSITION;
95}
96
97/*
98 * Allocate or reallocate the position table.
99 */
100public void pos_init(void)
101{
102	struct scrpos scrpos;
103
104	if (sc_height <= table_size)
105		return;
106	/*
107	 * If we already have a table, remember the first line in it
108	 * before we free it, so we can copy that line to the new table.
109	 */
110	if (table != NULL)
111	{
112		get_scrpos(&scrpos, TOP);
113		free((char*)table);
114	} else
115		scrpos.pos = NULL_POSITION;
116	table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
117	table_size = sc_height;
118	pos_clear();
119	if (scrpos.pos != NULL_POSITION)
120		table[scrpos.ln-1] = scrpos.pos;
121}
122
123/*
124 * See if the byte at a specified position is currently on the screen.
125 * Check the position table to see if the position falls within its range.
126 * Return the position table entry if found, -1 if not.
127 */
128public int onscreen(POSITION pos)
129{
130	int i;
131
132	if (pos < table[0])
133		return (-1);
134	for (i = 1;  i < sc_height;  i++)
135		if (pos < table[i])
136			return (i-1);
137	return (-1);
138}
139
140/*
141 * See if the entire screen is empty.
142 */
143public int empty_screen(void)
144{
145	return (empty_lines(0, sc_height-1));
146}
147
148public int empty_lines(int s, int e)
149{
150	int i;
151
152	for (i = s;  i <= e;  i++)
153		if (table[i] != NULL_POSITION && table[i] != 0)
154			return (0);
155	return (1);
156}
157
158/*
159 * Get the current screen position.
160 * The screen position consists of both a file position and
161 * a screen line number where the file position is placed on the screen.
162 * Normally the screen line number is 0, but if we are positioned
163 * such that the top few lines are empty, we may have to set
164 * the screen line to a number > 0.
165 */
166public void get_scrpos(struct scrpos *scrpos, int where)
167{
168	int i;
169	int dir;
170	int last;
171
172	switch (where)
173	{
174	case TOP:
175		i = 0; dir = +1; last = sc_height-2;
176		break;
177	case BOTTOM: case BOTTOM_PLUS_ONE:
178		i = sc_height-2; dir = -1; last = 0;
179		break;
180	default:
181		i = where;
182		if (table[i] == NULL_POSITION) {
183			scrpos->pos = NULL_POSITION;
184			return;
185		}
186		/* Values of dir and last don't matter after this. */
187		break;
188	}
189
190	/*
191	 * Find the first line on the screen which has something on it,
192	 * and return the screen line number and the file position.
193	 */
194	for (;; i += dir)
195	{
196		if (table[i] != NULL_POSITION)
197		{
198			scrpos->ln = i+1;
199			scrpos->pos = table[i];
200			return;
201		}
202		if (i == last) break;
203	}
204	/*
205	 * The screen is empty.
206	 */
207	scrpos->pos = NULL_POSITION;
208}
209
210/*
211 * Adjust a screen line number to be a simple positive integer
212 * in the range { 0 .. sc_height-2 }.
213 * (The bottom line, sc_height-1, is reserved for prompts, etc.)
214 * The given "sline" may be in the range { 1 .. sc_height-1 }
215 * to refer to lines relative to the top of the screen (starting from 1),
216 * or it may be in { -1 .. -(sc_height-1) } to refer to lines
217 * relative to the bottom of the screen.
218 */
219public int sindex_from_sline(int sline)
220{
221	/*
222	 * Negative screen line number means
223	 * relative to the bottom of the screen.
224	 */
225	if (sline < 0)
226		sline += sc_height;
227	/*
228	 * Can't be less than 1 or greater than sc_height.
229	 */
230	if (sline <= 0)
231		sline = 1;
232	if (sline > sc_height)
233		sline = sc_height;
234	/*
235	 * Return zero-based line number, not one-based.
236	 */
237	return (sline-1);
238}
239