xref: /freebsd/contrib/less/position.c (revision 1e413cf93298b5b97441a21d9a50fdcd0ee9945e)
1 /*
2  * Copyright (C) 1984-2007  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 about less, or for information on how to
8  * contact the author, see the README file.
9  */
10 
11 
12 /*
13  * Routines dealing with the "position" table.
14  * This is a table which tells the position (in the input file) of the
15  * first char on each currently displayed line.
16  *
17  * {{ The position table is scrolled by moving all the entries.
18  *    Would be better to have a circular table
19  *    and just change a couple of pointers. }}
20  */
21 
22 #include "less.h"
23 #include "position.h"
24 
25 static POSITION *table = NULL;	/* The position table */
26 static int table_size;
27 
28 extern int sc_width, sc_height;
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  */
39 	public POSITION
40 position(where)
41 	int where;
42 {
43 	switch (where)
44 	{
45 	case BOTTOM:
46 		where = sc_height - 2;
47 		break;
48 	case BOTTOM_PLUS_ONE:
49 		where = sc_height - 1;
50 		break;
51 	case MIDDLE:
52 		where = (sc_height - 1) / 2;
53 	}
54 	return (table[where]);
55 }
56 
57 /*
58  * Add a new file position to the bottom of the position table.
59  */
60 	public void
61 add_forw_pos(pos)
62 	POSITION pos;
63 {
64 	register int i;
65 
66 	/*
67 	 * Scroll the position table up.
68 	 */
69 	for (i = 1;  i < sc_height;  i++)
70 		table[i-1] = table[i];
71 	table[sc_height - 1] = pos;
72 }
73 
74 /*
75  * Add a new file position to the top of the position table.
76  */
77 	public void
78 add_back_pos(pos)
79 	POSITION pos;
80 {
81 	register int i;
82 
83 	/*
84 	 * Scroll the position table down.
85 	 */
86 	for (i = sc_height - 1;  i > 0;  i--)
87 		table[i] = table[i-1];
88 	table[0] = pos;
89 }
90 
91 /*
92  * Initialize the position table, done whenever we clear the screen.
93  */
94 	public void
95 pos_clear()
96 {
97 	register int i;
98 
99 	for (i = 0;  i < sc_height;  i++)
100 		table[i] = NULL_POSITION;
101 }
102 
103 /*
104  * Allocate or reallocate the position table.
105  */
106 	public void
107 pos_init()
108 {
109 	struct scrpos scrpos;
110 
111 	if (sc_height <= table_size)
112 		return;
113 	/*
114 	 * If we already have a table, remember the first line in it
115 	 * before we free it, so we can copy that line to the new table.
116 	 */
117 	if (table != NULL)
118 	{
119 		get_scrpos(&scrpos);
120 		free((char*)table);
121 	} else
122 		scrpos.pos = NULL_POSITION;
123 	table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
124 	table_size = sc_height;
125 	pos_clear();
126 	if (scrpos.pos != NULL_POSITION)
127 		table[scrpos.ln-1] = scrpos.pos;
128 }
129 
130 /*
131  * See if the byte at a specified position is currently on the screen.
132  * Check the position table to see if the position falls within its range.
133  * Return the position table entry if found, -1 if not.
134  */
135 	public int
136 onscreen(pos)
137 	POSITION pos;
138 {
139 	register int i;
140 
141 	if (pos < table[0])
142 		return (-1);
143 	for (i = 1;  i < sc_height;  i++)
144 		if (pos < table[i])
145 			return (i-1);
146 	return (-1);
147 }
148 
149 /*
150  * See if the entire screen is empty.
151  */
152 	public int
153 empty_screen()
154 {
155 	return (empty_lines(0, sc_height-1));
156 }
157 
158 	public int
159 empty_lines(s, e)
160 	int s;
161 	int e;
162 {
163 	register int i;
164 
165 	for (i = s;  i <= e;  i++)
166 		if (table[i] != NULL_POSITION)
167 			return (0);
168 	return (1);
169 }
170 
171 /*
172  * Get the current screen position.
173  * The screen position consists of both a file position and
174  * a screen line number where the file position is placed on the screen.
175  * Normally the screen line number is 0, but if we are positioned
176  * such that the top few lines are empty, we may have to set
177  * the screen line to a number > 0.
178  */
179 	public void
180 get_scrpos(scrpos)
181 	struct scrpos *scrpos;
182 {
183 	register int i;
184 
185 	/*
186 	 * Find the first line on the screen which has something on it,
187 	 * and return the screen line number and the file position.
188 	 */
189 	for (i = 0; i < sc_height;  i++)
190 		if (table[i] != NULL_POSITION)
191 		{
192 			scrpos->ln = i+1;
193 			scrpos->pos = table[i];
194 			return;
195 		}
196 	/*
197 	 * The screen is empty.
198 	 */
199 	scrpos->pos = NULL_POSITION;
200 }
201 
202 /*
203  * Adjust a screen line number to be a simple positive integer
204  * in the range { 0 .. sc_height-2 }.
205  * (The bottom line, sc_height-1, is reserved for prompts, etc.)
206  * The given "sline" may be in the range { 1 .. sc_height-1 }
207  * to refer to lines relative to the top of the screen (starting from 1),
208  * or it may be in { -1 .. -(sc_height-1) } to refer to lines
209  * relative to the bottom of the screen.
210  */
211 	public int
212 adjsline(sline)
213 	int sline;
214 {
215 	/*
216 	 * Negative screen line number means
217 	 * relative to the bottom of the screen.
218 	 */
219 	if (sline < 0)
220 		sline += sc_height;
221 	/*
222 	 * Can't be less than 1 or greater than sc_height-1.
223 	 */
224 	if (sline <= 0)
225 		sline = 1;
226 	if (sline >= sc_height)
227 		sline = sc_height - 1;
228 	/*
229 	 * Return zero-based line number, not one-based.
230 	 */
231 	return (sline-1);
232 }
233