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