uemacs/line.c

/*	line.c
 *
 * The functions in this file are a general set of line management utilities.
 * They are the only routines that touch the text. They also touch the buffer
 * and window structures, to make sure that the necessary updating gets done.
 * There are routines in this file that handle the kill buffer too. It isn't
 * here for any good reason.
 *
 * Note that this code only updates the dot and mark values in the window list.
 * Since all the code acts on the current window, the buffer that we are
 * editing must be being displayed, which means that "b_nwnd" is non zero,
 * which means that the dot and mark values in the buffer headers are nonsense.
 *
 */

#include "line.h"

#include <assert.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "buffer.h"
#include "estruct.h"
#include "mlout.h"
#include "window.h"


int tabwidth = 8 ;			/* column span of a tab */

static int ldelnewline( void) ;

/* The editor holds deleted text chunks in the struct kill buffer. The
 * kill buffer is logically a stream of ascii characters, however
 * due to its unpredicatable size, it gets implemented as a linked
 * list of chunks. (The d_ prefix is for "deleted" text, as k_
 * was taken up by the keycode structure).
 */

#define	KBLOCK	250		/* sizeof kill buffer chunks    */

struct kill {
	struct kill *d_next;   /* Link to next chunk, NULL if last. */
	char d_chunk[KBLOCK];  /* Deleted text. */
};

static struct kill *kbufp = NULL ;	/* current kill buffer chunk pointer */
static struct kill *kbufh = NULL ;	/* kill buffer header pointer */
static int kused = KBLOCK ;		/* # of bytes used in kill buffer */
static int klen ;					/* length of kill buffer content */
static char *value = NULL ;			/* temp buffer for value */

/*
 * return some of the contents of the kill buffer
 */
char *getkill( void) {
	struct kill *kp ;
	char *cp ;

	if (kbufh == NULL)
		/* no kill buffer....just a null string */
		return "" ;

	if( value != NULL)
		free( value) ;

	value = (char *) malloc( klen + 1) ;
	cp = value ;
	for( kp = kbufh ; kp != NULL ; kp = kp->d_next) {
		int size ;
		
		if( kp->d_next != NULL)
			size = KBLOCK ;
		else
			size = kused ;
			
		memcpy( cp, kp->d_chunk, size) ;
		cp += size ;
	}
	
	*cp = 0 ;

	/* and return the constructed value */
	return value;
}

/*
 * Move the cursor backwards by "n" characters. If "n" is less than zero call
 * "forwchar" to actually do the move. Otherwise compute the new cursor
 * location. Error if you try and move out of the buffer. Set the flag if the
 * line pointer for dot changes.
 */
static unsigned utf8_revdelta( unsigned char *p, unsigned pos) {
	unsigned delta = 0 ;

	if( (*p & 0xC0) == 0x80) {
		unsigned char c ;

		c = *--p ;
		if( (c & 0xE0) == 0xC0)	/* valid 2 bytes unicode seq */
			delta = 1 ;
		else if( ((c & 0xC0) == 0x80) && (pos > 1)) {
			c = *--p ;
			if( (c & 0xF0) == 0xE0)	/* valid 3 bytes unicode seq */
				delta = 2 ;
			else if( ((c & 0xC0) == 0x80) && (pos > 2))
				if( (p[ -1] & 0xF8) == 0xF0)	/* valid 4 bytes unicode seq */
					delta = 3 ;
		}
	}

	return delta ;
}

boolean backchar( int f, int n) {
	assert( f == TRUE || (f == FALSE && n == 1)) ;
	if( n < 0)
		return forwchar( f, -n) ;

	while( n--) {
		if( curwp->w_doto == 0) {	/* at beginning of line */
			line_p lp ;

			lp = lback( curwp->w_dotp) ;
			if( lp == curbp->b_linep)	/* at beginning of buffer */
				return FALSE ;

			curwp->w_dotp = lp ;
			curwp->w_doto = llength( lp) ;
			curwp->w_flag |= WFMOVE ;
		} else {
			unsigned pos ;
			
			pos = curwp->w_doto -= 1 ;
			if( pos > 0)
				curwp->w_doto -= utf8_revdelta( (unsigned char *) &( (curwp->w_dotp)->l_text[ pos]), pos) ;
		}
	}

	return TRUE ;
}

/*
 * Move the cursor forwards by "n" characters. If "n" is less than zero call
 * "backchar" to actually do the move. Otherwise compute the new cursor
 * location, and move ".". Error if you try and move off the end of the
 * buffer. Set the flag if the line pointer for dot changes.
 */
boolean forwchar( int f, int n) {
	assert( f == TRUE || (f == FALSE && n == 1)) ;
	if( n < 0)
		return backchar( f, -n) ;

	while( n--) {
		int len = llength( curwp->w_dotp) ;
		if( curwp->w_doto == len) {	/* at end of line */
			if( curwp->w_dotp == curbp->b_linep)	/* at end of buffer */
				return FALSE ;

			curwp->w_dotp = lforw( curwp->w_dotp) ;
			curwp->w_doto = 0 ;
			curwp->w_flag |= WFMOVE ;
		} else {
			unicode_t unc ;
			unsigned bytes ;
			
			bytes = utf8_to_unicode( curwp->w_dotp->l_text, curwp->w_doto, len, &unc) ;
			curwp->w_doto += bytes ;
		}
	}

	return TRUE ;
}

/*
 * This routine allocates a block of memory large enough to hold a struct line
 * containing "used" characters. The block is always rounded up a bit. Return
 * a pointer to the new block, or NULL if there isn't any memory left. Print a
 * message in the message line if no space.
 */
line_p lalloc( int used) {
#define	BLOCK_SIZE 16	/* Line block chunk size. */
	line_p lp ;
	int size ;

/*	size = used + BLOCK_SIZE - used % BLOCK_SIZE ; */
	size = (used + BLOCK_SIZE) & ~(BLOCK_SIZE - 1) ; /* as BLOCK_SIZE is power of 2 */
	lp = (line_p) malloc( offsetof( struct line, l_text) + size) ;
	if( lp == NULL)
		mloutstr( "(OUT OF MEMORY)") ;
	else {
		lp->l_size = size ;
		lp->l_used = used ;
	}

	return lp ;
}

/*
 * Delete line "lp". Fix all of the links that might point at it (they are
 * moved to offset 0 of the next line. Unlink the line from whatever buffer it
 * might be in. Release the memory. The buffers are updated too; the magic
 * conditions described in the above comments don't hold here.
 */
void lfree( line_p lp) {
	struct buffer *bp;
	struct window *wp;

	wp = wheadp;
	while (wp != NULL) {
		if (wp->w_linep == lp)
			wp->w_linep = lp->l_fp;
		if (wp->w_dotp == lp) {
			wp->w_dotp = lp->l_fp;
			wp->w_doto = 0;
		}
		if (wp->w_markp == lp) {
			wp->w_markp = lp->l_fp;
			wp->w_marko = 0;
		}
		wp = wp->w_wndp;
	}
	bp = bheadp;
	while (bp != NULL) {
		if (bp->b_nwnd == 0) {
			if (bp->b_dotp == lp) {
				bp->b_dotp = lp->l_fp;
				bp->b_doto = 0;
			}
			if (bp->b_markp == lp) {
				bp->b_markp = lp->l_fp;
				bp->b_marko = 0;
			}
		}
		bp = bp->b_bufp;
	}
	lp->l_bp->l_fp = lp->l_fp;
	lp->l_fp->l_bp = lp->l_bp;
	free((char *) lp);
}

/*
 * This routine gets called when a character is changed in place in the current
 * buffer. It updates all of the required flags in the buffer and window
 * system. The flag used is passed as an argument; if the buffer is being
 * displayed in more than 1 window we change EDIT t HARD. Set MODE if the
 * mode line needs to be updated (the "*" has to be set).
 */
void lchange(int flag)
{
	struct window *wp;

	if (curbp->b_nwnd != 1)	/* Ensure hard.     */
		flag = WFHARD;
	if ((curbp->b_flag & BFCHG) == 0) {	/* First change, so     */
		flag |= WFMODE;	/* update mode lines.   */
		curbp->b_flag |= BFCHG;
	}
	wp = wheadp;
	while (wp != NULL) {
		if (wp->w_bufp == curbp)
			wp->w_flag |= flag;
		wp = wp->w_wndp;
	}
}

/*
 * insert spaces forward into text
 *
 * int f, n;		default flag and numeric argument
 */
int insspace(int f, int n)
{
	linsert(n, ' ');
	backchar(f, n);
	return TRUE;
}

/*
 * linstr -- Insert a string at the current point
 */

int linstr( char *instr) {
	int status = TRUE ;

	if( instr != NULL) {
		unicode_t tmpc ;

		while( (tmpc = *instr++ & 0xFF)) {
			status =
			    (tmpc == '\n' ? lnewline() : (int) linsert_byte( 1, tmpc)) ;

			/* Insertion error? */
			if( status != TRUE) {
				mloutstr( "%Out of memory while inserting") ;
				return status ;
			}
		}
	}

	return status ;
}

/*
 * Insert "n" copies of the character "c" at the current location of dot. In
 * the easy case all that happens is the text is stored in the line. In the
 * hard case, the line has to be reallocated. When the window list is updated,
 * take special care; I screwed it up once. You always update dot in the
 * current window. You update mark, and a dot in another window, if it is
 * greater than the place where you did the insert. Return TRUE if all is
 * well, and FALSE on errors.
 */

boolean linsert_byte( int n, int c) {
	char *cp1;
	char *cp2;
	struct line *lp1;
	struct line *lp2;
	struct line *lp3;
	int doto;
	int i;
	struct window *wp;

	assert( (curbp->b_mode & MDVIEW) == 0) ;
#if 0
	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */
#endif
	lchange(WFEDIT);
	lp1 = curwp->w_dotp;	/* Current line         */
	if (lp1 == curbp->b_linep) {	/* At the end: special  */
		if (curwp->w_doto != 0) {
			mloutstr( "bug: linsert") ;
			return FALSE;
		}
		if ((lp2 = lalloc(n)) == NULL)	/* Allocate new line        */
			return FALSE;
		lp3 = lp1->l_bp;	/* Previous line        */
		lp3->l_fp = lp2;	/* Link in              */
		lp2->l_fp = lp1;
		lp1->l_bp = lp2;
		lp2->l_bp = lp3;
		for (i = 0; i < n; ++i)
			lp2->l_text[i] = c;
		curwp->w_dotp = lp2;
		curwp->w_doto = n;
		return TRUE;
	}
	doto = curwp->w_doto;	/* Save for later.      */
	if (lp1->l_used + n > lp1->l_size) {	/* Hard: reallocate     */
		if ((lp2 = lalloc(lp1->l_used + n)) == NULL)
			return FALSE;
		cp1 = &lp1->l_text[0];
		cp2 = &lp2->l_text[0];
		while (cp1 != &lp1->l_text[doto])
			*cp2++ = *cp1++;
		cp2 += n;
		while (cp1 != &lp1->l_text[lp1->l_used])
			*cp2++ = *cp1++;
		lp1->l_bp->l_fp = lp2;
		lp2->l_fp = lp1->l_fp;
		lp1->l_fp->l_bp = lp2;
		lp2->l_bp = lp1->l_bp;
		free((char *) lp1);
	} else {		/* Easy: in place       */
		lp2 = lp1;	/* Pretend new line     */
		lp2->l_used += n;
		cp2 = &lp1->l_text[lp1->l_used];
		cp1 = cp2 - n;
		while (cp1 != &lp1->l_text[doto])
			*--cp2 = *--cp1;
	}
	for (i = 0; i < n; ++i)	/* Add the characters       */
		lp2->l_text[doto + i] = c;
	wp = wheadp;		/* Update windows       */
	while (wp != NULL) {
		if (wp->w_linep == lp1)
			wp->w_linep = lp2;
		if (wp->w_dotp == lp1) {
			wp->w_dotp = lp2;
			if (wp == curwp || wp->w_doto > doto)
				wp->w_doto += n;
		}
		if (wp->w_markp == lp1) {
			wp->w_markp = lp2;
			if (wp->w_marko > doto)
				wp->w_marko += n;
		}
		wp = wp->w_wndp;
	}
	return TRUE;
}

int linsert( int n, unicode_t c) {
	assert( n >= 0) ;
	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */

	if( n > 0) {
		char utf8[ 4] ;
		int bytes ;

		bytes = unicode_to_utf8(c, utf8) ;
		if (bytes == 1)
			return linsert_byte(n, (unsigned char) utf8[0]);

		do {
			int j ;

			for( j = 0 ; j < bytes ; j += 1)
				if( !linsert_byte( 1, (unsigned char) utf8[ j]))
					return FALSE ;
		} while( --n > 0) ;
	}

	return TRUE;
}

/*
 * Overwrite a character into the current line at the current position
 *
 * int c;	character to overwrite on current position
 */
static int lowrite( int c) {
	if( curwp->w_doto < curwp->w_dotp->l_used
	&& (
		lgetc(curwp->w_dotp, curwp->w_doto) != '\t' ||
		((curwp->w_doto) % tabwidth) == (tabwidth - 1)
	))
		ldelchar( 1, FALSE) ;

	return linsert( 1, c) ;
}

/*
 * lover -- Overwrite a string at the current point
 */
int lover( char *ostr) {
	int status = TRUE ;

	if (ostr != NULL) {
		char tmpc ;

		while( (tmpc = *ostr++)) {
			status =
			    (tmpc == '\n' ? lnewline() : lowrite(tmpc));

			/* Insertion error? */
			if( status != TRUE) {
				mloutstr( "%Out of memory while overwriting") ;
				return status ;
			}
		}
	}
	
	return status ;
}

/*
 * Insert a newline into the buffer at the current location of dot in the
 * current window. The funny ass-backwards way it does things is not a botch;
 * it just makes the last line in the file not a special case. Return TRUE if
 * everything works out and FALSE on error (memory allocation failure). The
 * update of dot and mark is a bit easier then in the above case, because the
 * split forces more updating.
 */
int lnewline(void)
{
	char *cp1;
	char *cp2;
	struct line *lp1;
	struct line *lp2;
	int doto;
	struct window *wp;

	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */
#if SCROLLCODE
	lchange(WFHARD | WFINS);
#else
	lchange(WFHARD);
#endif
	lp1 = curwp->w_dotp;	/* Get the address and  */
	doto = curwp->w_doto;	/* offset of "."        */
	if ((lp2 = lalloc(doto)) == NULL)	/* New first half line      */
		return FALSE;
	cp1 = &lp1->l_text[0];	/* Shuffle text around  */
	cp2 = &lp2->l_text[0];
	while (cp1 != &lp1->l_text[doto])
		*cp2++ = *cp1++;
	cp2 = &lp1->l_text[0];
	while (cp1 != &lp1->l_text[lp1->l_used])
		*cp2++ = *cp1++;
	lp1->l_used -= doto;
	lp2->l_bp = lp1->l_bp;
	lp1->l_bp = lp2;
	lp2->l_bp->l_fp = lp2;
	lp2->l_fp = lp1;
	wp = wheadp;		/* Windows              */
	while (wp != NULL) {
		if (wp->w_linep == lp1)
			wp->w_linep = lp2;
		if (wp->w_dotp == lp1) {
			if (wp->w_doto < doto)
				wp->w_dotp = lp2;
			else
				wp->w_doto -= doto;
		}
		if (wp->w_markp == lp1) {
			if (wp->w_marko < doto)
				wp->w_markp = lp2;
			else
				wp->w_marko -= doto;
		}
		wp = wp->w_wndp;
	}
	return TRUE;
}

int lgetchar( unicode_t *c) {
	if( curwp->w_dotp->l_used == curwp->w_doto) {
		*c = (curbp->b_mode & MDDOS) ? '\r' : '\n' ;
		return 1 ;
	} else
		return utf8_to_unicode( curwp->w_dotp->l_text, curwp->w_doto,
												llength( curwp->w_dotp), c) ;
}

/*
 * ldelete() really fundamentally works on bytes, not characters.
 * It is used for things like "scan 5 words forwards, and remove
 * the bytes we scanned".
 *
 * If you want to delete characters, use ldelchar().
 */
boolean ldelchar( long n, boolean kflag) {
/* testing for read only mode is done by ldelete() */
	while (n-- > 0) {
		unicode_t c;
		if (!ldelete(lgetchar(&c), kflag))
			return FALSE;
	}
	return TRUE;
}

/*
 * This function deletes "n" bytes, starting at dot. It understands how do deal
 * with end of lines, etc. It returns TRUE if all of the characters were
 * deleted, and FALSE if they were not (because dot ran into the end of the
 * buffer. The "kflag" is TRUE if the text should be put in the kill buffer.
 *
 * long n;		# of chars to delete
 * int kflag;		 put killed text in kill buffer flag
 */
boolean ldelete( long n, boolean kflag) {
	char *cp1;
	char *cp2;
	struct line *dotp;
	int doto;
	int chunk;
	struct window *wp;

	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */

	while( n > 0) {
		dotp = curwp->w_dotp;
		doto = curwp->w_doto;
		if (dotp == curbp->b_linep)	/* Hit end of buffer.       */
			return FALSE;
		chunk = dotp->l_used - doto;	/* Size of chunk.       */
		if (chunk > n)
			chunk = n;
		if (chunk == 0) {	/* End of line, merge.  */
#if SCROLLCODE
			lchange(WFHARD | WFKILLS);
#else
			lchange(WFHARD);
#endif
			if (ldelnewline() == FALSE
			    || (kflag != FALSE && kinsert('\n') == FALSE))
				return FALSE;
			--n;
			continue;
		}
		lchange(WFEDIT);
		cp1 = &dotp->l_text[doto];	/* Scrunch text.        */
		cp2 = cp1 + chunk;
		if (kflag != FALSE) {	/* Kill?                */
			while (cp1 != cp2) {
				if (kinsert(*cp1) == FALSE)
					return FALSE;
				++cp1;
			}
			cp1 = &dotp->l_text[doto];
		}
		while (cp2 != &dotp->l_text[dotp->l_used])
			*cp1++ = *cp2++;
		dotp->l_used -= chunk;
		wp = wheadp;	/* Fix windows          */
		while (wp != NULL) {
			if (wp->w_dotp == dotp && wp->w_doto >= doto) {
				wp->w_doto -= chunk;
				if (wp->w_doto < doto)
					wp->w_doto = doto;
			}
			if (wp->w_markp == dotp && wp->w_marko >= doto) {
				wp->w_marko -= chunk;
				if (wp->w_marko < doto)
					wp->w_marko = doto;
			}
			wp = wp->w_wndp;
		}
		n -= chunk;
	}
	return TRUE;
}

/*
 * getctext:	grab and return a string with the text of
 *		the current line
 */
char *getctext( void) {
	line_p	lp ;	/* line to copy */
	int size;	/* length of line to return */
	static int	rsize = 0 ;
	static char *rline ;	/* line to return */

	/* find the contents of the current line and its length */
	lp = curwp->w_dotp;
	size = lp->l_used;
	if( size >= rsize) {
		if( rsize)
			free( rline) ;

		rsize = size + 1 ;
		rline = malloc( rsize) ;
		if( rline == NULL) {
			rsize = 0 ;
			return "" ;
		}
	}

	/* copy it across */
	memcpy( rline, lp->l_text, size) ;
	rline[ size] = 0 ;
	return rline ;
}

/*
 * Delete a newline. Join the current line with the next line. If the next line
 * is the magic header line always return TRUE; merging the last line with the
 * header line can be thought of as always being a successful operation, even
 * if nothing is done, and this makes the kill buffer work "right". Easy cases
 * can be done by shuffling data around. Hard cases require that lines be moved
 * about in memory. Return FALSE on error and TRUE if all looks ok. Called by
 * "ldelete" only.
 */
static int ldelnewline(void)
{
	char *cp1;
	char *cp2;
	struct line *lp1;
	struct line *lp2;
	struct line *lp3;
	struct window *wp;

	assert( (curbp->b_mode & MDVIEW) == 0) ;
#if 0
	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */
#endif
	lp1 = curwp->w_dotp;
	lp2 = lp1->l_fp;
	if (lp2 == curbp->b_linep) {	/* At the buffer end.   */
		if (lp1->l_used == 0)	/* Blank line.              */
			lfree(lp1);
		return TRUE;
	}
	if (lp2->l_used <= lp1->l_size - lp1->l_used) {
		cp1 = &lp1->l_text[lp1->l_used];
		cp2 = &lp2->l_text[0];
		while (cp2 != &lp2->l_text[lp2->l_used])
			*cp1++ = *cp2++;
		wp = wheadp;
		while (wp != NULL) {
			if (wp->w_linep == lp2)
				wp->w_linep = lp1;
			if (wp->w_dotp == lp2) {
				wp->w_dotp = lp1;
				wp->w_doto += lp1->l_used;
			}
			if (wp->w_markp == lp2) {
				wp->w_markp = lp1;
				wp->w_marko += lp1->l_used;
			}
			wp = wp->w_wndp;
		}
		lp1->l_used += lp2->l_used;
		lp1->l_fp = lp2->l_fp;
		lp2->l_fp->l_bp = lp1;
		free((char *) lp2);
		return TRUE;
	}
	if ((lp3 = lalloc(lp1->l_used + lp2->l_used)) == NULL)
		return FALSE;
	cp1 = &lp1->l_text[0];
	cp2 = &lp3->l_text[0];
	while (cp1 != &lp1->l_text[lp1->l_used])
		*cp2++ = *cp1++;
	cp1 = &lp2->l_text[0];
	while (cp1 != &lp2->l_text[lp2->l_used])
		*cp2++ = *cp1++;
	lp1->l_bp->l_fp = lp3;
	lp3->l_fp = lp2->l_fp;
	lp2->l_fp->l_bp = lp3;
	lp3->l_bp = lp1->l_bp;
	wp = wheadp;
	while (wp != NULL) {
		if (wp->w_linep == lp1 || wp->w_linep == lp2)
			wp->w_linep = lp3;
		if (wp->w_dotp == lp1)
			wp->w_dotp = lp3;
		else if (wp->w_dotp == lp2) {
			wp->w_dotp = lp3;
			wp->w_doto += lp1->l_used;
		}
		if (wp->w_markp == lp1)
			wp->w_markp = lp3;
		else if (wp->w_markp == lp2) {
			wp->w_markp = lp3;
			wp->w_marko += lp1->l_used;
		}
		wp = wp->w_wndp;
	}
	free((char *) lp1);
	free((char *) lp2);
	return TRUE;
}

/*
 * Delete all of the text saved in the kill buffer. Called by commands when a
 * new kill context is being created. The kill buffer array is released, just
 * in case the buffer has grown to immense size. No errors.
 */
void kdelete(void)
{
	struct kill *kp;		/* ptr to scan kill buffer chunk list */

	if (kbufh != NULL) {

		/* first, delete all the chunks */
		kbufp = kbufh;
		while (kbufp != NULL) {
			kp = kbufp->d_next;
			free(kbufp);
			kbufp = kp;
		}

		/* and reset all the kill buffer pointers */
		kbufh = kbufp = NULL;
		kused = KBLOCK;
		klen = 0 ;
		if( value != NULL) {
			free( value) ;
			value = NULL ;
		}
	}
}

/*
 * Insert a character to the kill buffer, allocating new chunks as needed.
 * Return TRUE if all is well, and FALSE on errors.
 *
 * int c;			character to insert in the kill buffer
 */
int kinsert(int c)
{
	struct kill *nchunk;		/* ptr to newly malloced chunk */

	/* check to see if we need a new chunk */
	if (kused >= KBLOCK) {
		if ((nchunk = (struct kill *)malloc(sizeof(struct kill))) == NULL)
			return FALSE;
		if( kbufh == NULL) {	/* set head ptr if first time */
			kbufh = nchunk;
			klen = 0 ;
		}

		if (kbufp != NULL)	/* point the current to this new one */
			kbufp->d_next = nchunk;
		kbufp = nchunk;
		kbufp->d_next = NULL;
		kused = 0;
	}

	/* and now insert the character */
	kbufp->d_chunk[kused++] = c;
	klen += 1 ;
	return TRUE;
}

/*
 * Yank text back from the kill buffer. This is really easy. All of the work
 * is done by the standard insert routines. All you do is run the loop, and
 * check for errors. Bound to "C-Y".
 */
int yank(int f, int n)
{
	int c;
	int i;
	char *sp;	/* pointer into string to insert */
	struct kill *kp;		/* pointer into kill buffer */

	if (curbp->b_mode & MDVIEW)	/* don't allow this command if      */
		return rdonly();	/* we are in read only mode     */
	if (n < 0)
		return FALSE;
	/* make sure there is something to yank */
	if (kbufh == NULL)
		return TRUE;	/* not an error, just nothing */

	/* for each time.... */
	while (n--) {
		kp = kbufh;
		while (kp != NULL) {
			if (kp->d_next == NULL)
				i = kused;
			else
				i = KBLOCK;
			sp = kp->d_chunk;
			while (i--) {
				if ((c = *sp++) == '\n') {
					if (lnewline() == FALSE)
						return FALSE;
				} else {
					if (linsert_byte(1, c) == FALSE)
						return FALSE;
				}
			}
			kp = kp->d_next;
		}
	}
	return TRUE;
}

/*
 * tell the user that this command is illegal while we are in
 * VIEW (read-only) mode
 */
boolean rdonly( void) {
	mloutfmt( "%B(Key illegal in VIEW mode)") ;
	return FALSE ;
}