harvey/sys/src/libbio/bgetc.c

/*
 * This file is part of the UCB release of Plan 9. It is subject to the license
 * terms in the LICENSE file found in the top-level directory of this
 * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No
 * part of the UCB release of Plan 9, including this file, may be copied,
 * modified, propagated, or distributed except according to the terms contained
 * in the LICENSE file.
 */

#include	<u.h>
#include	<libc.h>
#include	<bio.h>

int
Bgetc(Biobufhdr *bp)
{
	int i;

loop:
	i = bp->icount;
	if(i != 0) {
		bp->icount = i+1;
		return bp->ebuf[i];
	}
	if(bp->state != Bractive) {
		if(bp->state == Bracteof)
			bp->state = Bractive;
		return Beof;
	}
	/*
	 * get next buffer, try to keep Bungetsize
	 * characters pre-catenated from the previous
	 * buffer to allow that many ungets.
	 */
	memmove(bp->bbuf-Bungetsize, bp->ebuf-Bungetsize, Bungetsize);
	i = read(bp->fid, bp->bbuf, bp->bsize);
	bp->gbuf = bp->bbuf;
	if(i <= 0) {
		bp->state = Bracteof;
		if(i < 0)
			bp->state = Binactive;
		return Beof;
	}
	if(i < bp->bsize) {
		memmove(bp->ebuf-i-Bungetsize, bp->bbuf-Bungetsize, i+Bungetsize);
		bp->gbuf = bp->ebuf-i;
	}
	bp->icount = -i;
	bp->offset += i;
	goto loop;
}

int
Bungetc(Biobufhdr *bp)
{

	if(bp->state == Bracteof)
		bp->state = Bractive;
	if(bp->state != Bractive)
		return Beof;
	bp->icount--;
	return 1;
}