Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S268166AbUIPQbD (ORCPT ); Thu, 16 Sep 2004 12:31:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S268425AbUIPQbB (ORCPT ); Thu, 16 Sep 2004 12:31:01 -0400 Received: from rproxy.gmail.com ([64.233.170.197]:26086 "EHLO mproxy.gmail.com") by vger.kernel.org with ESMTP id S268430AbUIPQHN (ORCPT ); Thu, 16 Sep 2004 12:07:13 -0400 Message-ID: <5d6b657504091609072c7be97c@mail.gmail.com> Date: Thu, 16 Sep 2004 18:07:07 +0200 From: Buddy Lucas Reply-To: Buddy Lucas To: Stelian Pop , Buddy Lucas , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [RFC, 2.6] a simple FIFO implementation In-Reply-To: <20040916155247.GI3146@crusoe.alcove-fr> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit References: <20040913135253.GA3118@crusoe.alcove-fr> <20040915153013.32e797c8.akpm@osdl.org> <20040916064320.GA9886@deep-space-9.dsnet> <20040916000438.46d91e94.akpm@osdl.org> <20040916104535.GA3146@crusoe.alcove-fr> <5d6b657504091608093b171e30@mail.gmail.com> <20040916152919.GG3146@crusoe.alcove-fr> <5d6b657504091608511f100109@mail.gmail.com> <20040916155247.GI3146@crusoe.alcove-fr> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1244 Lines: 37 On Thu, 16 Sep 2004 17:52:47 +0200, Stelian Pop wrote: > On Thu, Sep 16, 2004 at 05:51:04PM +0200, Buddy Lucas wrote: > > > > No, because the type is *unsigned* int. > > > > Indeed, that would exactly be the reason *why* this would fail. ;-) > > > > The expression fifo->size - fifo->tail + fifo->head might be negative > > at some point, right? (fifo->head has wrapped to some small value and > > fifo->tail > fifo->size) > > And what is the value of an unsigned int holding that 'negative' value ? :) > Which unsigned int?! ;-) The expression a - b is negative for unsigned ints a and b where a < b. So, your unsigned ints "total" and "remaining" won't be negative of course, but they won't reflect what is actually left in the buffer; they will equal the value of len (in some cases) after fifo->head has wrapped (because of the unsignedness) and fifo->tail has not. Which would not be correct. Cheers, Buddy > > > Stelian. > -- > Stelian Pop > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/