Usenet 1994 January/usenetsourcesnewsgroupsinfomagicjanuary1994.iso/sources/unix/volume16/less5/part03/input.c

C/C++ Source or Header | 1988-09-22 | 4.2 KB | 201 lines

/*
 * High level routines dealing with getting lines of input
 * from the file being viewed.
 *
 * When we speak of "lines" here, we mean PRINTABLE lines;
 * lines processed with respect to the screen width.
 * We use the term "raw line" to refer to lines simply
 * delimited by newlines; not processed with respect to screen width.
 */

#include "less.h"

extern int squeeze;
extern int sigs;
extern char *line;

/*
 * Get the next line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the NEXT line.  The line obtained is the line starting at curr_pos.
 */
    public POSITION
forw_line(curr_pos)
    POSITION curr_pos;
{
    POSITION new_pos;
    register int c;

    if (curr_pos == NULL_POSITION || ch_seek(curr_pos))
        return (NULL_POSITION);

    c = ch_forw_get();
    if (c == EOI)
        return (NULL_POSITION);

    prewind();
    for (;;)
    {
        if (sigs)
            return (NULL_POSITION);
        if (c == '\n' || c == EOI)
        {
            /*
             * End of the line.
             */
            new_pos = ch_tell();
            break;
        }

        /*
         * Append the char to the line and get the next char.
         */
        if (pappend(c))
        {
            /*
             * The char won't fit in the line; the line
             * is too long to print in the screen width.
             * End the line here.
             */
            new_pos = ch_tell() - 1;
            break;
        }
        c = ch_forw_get();
    }
    (void) pappend('\0');

    if (squeeze && *line == '\0')
    {
        /*
         * This line is blank.
         * Skip down to the last contiguous blank line
         * and pretend it is the one which we are returning.
         */
        while ((c = ch_forw_get()) == '\n')
            if (sigs)
                return (NULL_POSITION);
        if (c != EOI)
            (void) ch_back_get();
        new_pos = ch_tell();
    }

    return (new_pos);
}

/*
 * Get the previous line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the PREVIOUS line.  The line obtained is the one starting at new_pos.
 */
    public POSITION
back_line(curr_pos)
    POSITION curr_pos;
{
    POSITION new_pos, begin_new_pos;
    int c;

    if (curr_pos == NULL_POSITION || curr_pos <= (POSITION)0 ||
        ch_seek(curr_pos-1))
        return (NULL_POSITION);

    if (squeeze)
    {
        /*
         * Find out if the "current" line was blank.
         */
        (void) ch_forw_get();    /* Skip the newline */
        c = ch_forw_get();    /* First char of "current" line */
        (void) ch_back_get();    /* Restore our position */
        (void) ch_back_get();

        if (c == '\n')
        {
            /*
             * The "current" line was blank.
             * Skip over any preceeding blank lines,
             * since we skipped them in forw_line().
             */
            while ((c = ch_back_get()) == '\n')
                if (sigs)
                    return (NULL_POSITION);
            if (c == EOI)
                return (NULL_POSITION);
            (void) ch_forw_get();
        }
    }

    /*
     * Scan backwards until we hit the beginning of the line.
     */
    for (;;)
    {
        if (sigs)
            return (NULL_POSITION);
        c = ch_back_get();
        if (c == '\n')
        {
            /*
             * This is the newline ending the previous line.
             * We have hit the beginning of the line.
             */
            new_pos = ch_tell() + 1;
            break;
        }
        if (c == EOI)
        {
            /*
             * We have hit the beginning of the file.
             * This must be the first line in the file.
             * This must, of course, be the beginning of the line.
             */
            new_pos = ch_tell();
            break;
        }
    }

    /*
     * Now scan forwards from the beginning of this line.
     * We keep discarding "printable lines" (based on screen width)
     * until we reach the curr_pos.
     *
     * {{ This algorithm is pretty inefficient if the lines
     *    are much longer than the screen width,
     *    but I don't know of any better way. }}
     */
    if (ch_seek(new_pos))
        return (NULL_POSITION);
    loop:
    begin_new_pos = new_pos;
    prewind();

    do
    {
        c = ch_forw_get();
        if (c == EOI || sigs)
            return (NULL_POSITION);
        new_pos++;
        if (c == '\n')
            break;
        if (pappend(c))
        {
            /*
             * Got a full printable line, but we haven't
             * reached our curr_pos yet.  Discard the line
             * and start a new one.
             */
            (void) pappend('\0');
            (void) ch_back_get();
            new_pos--;
            goto loop;
        }
    } while (new_pos < curr_pos);

    (void) pappend('\0');

    return (begin_new_pos);
}