Plan 9 Sam's buffer data management

sam_insert.c

void
bufinsert(Buffer *b, uint q0, Rune *s, uint n)
{
	uint i, m, t, off;

	if(q0 > b->nc)
		panic("internal error: bufinsert");

	while(n > 0){
		setcache(b, q0);
		off = q0-b->cq;
		if(b->cnc+n <= Maxblock){
			/* Everything fits in one block. */
			t = b->cnc+n;
			m = n;
			if(b->bl == nil){	/* allocate */
				if(b->cnc != 0)
					panic("internal error: bufinsert1 cnc!=0");
				addblock(b, 0, t);
				b->cbi = 0;
			}
			sizecache(b, t);
			runemove(b->c+off+m, b->c+off, b->cnc-off);
			runemove(b->c+off, s, m);
			b->cnc = t;
			goto Tail;
		}
		/*
		 * We must make a new block.  If q0 is at
		 * the very beginning or end of this block,
		 * just make a new block and fill it.
		 */
		if(q0==b->cq || q0==b->cq+b->cnc){
			if(b->cdirty)
				flush(b);
			m = min(n, Maxblock);
			if(b->bl == nil){	/* allocate */
				if(b->cnc != 0)
					panic("internal error: bufinsert2 cnc!=0");
				i = 0;
			}else{
				i = b->cbi;
				if(q0 > b->cq)
					i++;
			}
			addblock(b, i, m);
			sizecache(b, m);
			runemove(b->c, s, m);
			b->cq = q0;
			b->cbi = i;
			b->cnc = m;
			goto Tail;
		}
		/*
		 * Split the block; cut off the right side and
		 * let go of it.
		 */
		m = b->cnc-off;
		if(m > 0){
			i = b->cbi+1;
			addblock(b, i, m);
			diskwrite(disk, &b->bl[i], b->c+off, m);
			b->cnc -= m;
		}
		/*
		 * Now at end of block.  Take as much input
		 * as possible and tack it on end of block.
		 */
		m = min(n, Maxblock-b->cnc);
		sizecache(b, b->cnc+m);
		runemove(b->c+b->cnc, s, m);
		b->cnc += m;
  Tail:
		b->nc += m;
		q0 += m;
		s += m;
		n -= m;
		b->cdirty = TRUE;
	}
}