Bill Joy's Ex/Vi's buffer data management

ex-vi_insert.c

/*
 * Append after line a lines returned by function f.
 * Be careful about intermediate states to avoid scramble
 * if an interrupt comes in.
 */
int 
append(int (*f)(void), line *a)
{
	register line *a1, *a2, *rdot;
	int nline;

	nline = 0;
	dot = a;
	if(FIXUNDO && !inopen && f!=getsub) {
		undap1 = undap2 = dot + 1;
		undkind = UNDCHANGE;
	}
	while ((*f)() == 0) {
		if (truedol >= endcore) { // If we've reached past the end of the buffer...
			if (morelines() < 0) { // ...Give us more lines.
				if (FIXUNDO && f == getsub) {
					undap1 = addr1;
					undap2 = addr2 + 1;
				}
				error(catgets(catd, 1, 39,
				"Out of memory@- too many lines in file"));
			}
		}
		nline++;
		a1 = truedol + 1;
		a2 = a1 + 1;
		dot++;
		undap2++;
		dol++;
		unddol++;
		truedol++;
		for (rdot = dot; a1 > rdot;)
			*--a2 = *--a1;
		*rdot = 0;
		putmark(rdot);
		if (f == gettty) {
			dirtcnt++;
			TSYNC();
		}
	}
	return (nline);
}


int 
morelines(void)
{
#ifdef	_SC_PAGESIZE
	static long pg;

	if (pg == 0) {
		pg = sysconf(_SC_PAGESIZE);
		if (pg <= 0 || pg >= 65536)
			pg = 4096;
		pg /= sizeof (line);
	}
	if ((char *)sbrk(pg * sizeof (line)) == (char *)-1)
		return (-1);
	endcore += pg;
	return (0);
#else	/* !_SC_PAGESIZE */
	if (sbrk(1024 * sizeof (line)) == (char *)-1)
		return (-1);
	endcore += 1024;
	return (0);
#endif	/* !_SC_PAGESIZE */
}