Date: Tue, 08 May 2007 14:51:42 -0700 From: Julian Elischer <julian@elischer.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-arch@freebsd.org, Giorgos Keramidas <keramida@freebsd.org>, Hans Petter Selasky <hselasky@c2i.net> Subject: Re: Missing LIST_PREV() ? Message-ID: <4640F0EE.2080206@elischer.org> In-Reply-To: <20070508211714.GQ83173@deviant.kiev.zoral.com.ua> References: <200705051617.34162.hselasky@c2i.net> <20070507202034.GA80846@kobe.laptop> <20070507202517.GA88340@kobe.laptop> <200705081128.25708.jhb@freebsd.org> <20070508211714.GQ83173@deviant.kiev.zoral.com.ua>
next in thread | previous in thread | raw e-mail | index | archive | help
Kostik Belousov wrote: > On Tue, May 08, 2007 at 11:28:25AM -0400, John Baldwin wrote: >> On Monday 07 May 2007 04:25:18 pm Giorgos Keramidas wrote: >>> On 2007-05-07 23:20, Giorgos Keramidas <keramida@freebsd.org> wrote: >>>> On 2007-05-05 16:17, Hans Petter Selasky <hselasky@c2i.net> wrote: >>>>> Hi, >>>>> >>>>> Why should LISTs only be forward traversable? The following piece of >>>>> code make lists backward traversable: >>>>> >>>>> /sys/sys/queue.h: >>>>> >>>>> +#define LIST_PREV(head,elm,field) \ >>>>> + (((elm) == LIST_FIRST(head)) ? ((__typeof(elm))0) : \ >>>>> + ((__typeof(elm))(((uint8_t *)((elm)->field.le_prev)) - \ >>>>> + ((uint8_t *)&LIST_NEXT((__typeof(elm))0,field))))) >>>>> >>>>> Any comments? >>>> 1. The use of (uint8_t *) casts is relatively ugly. >> Looks like an ugly version of offsetof() >> > ... >> I'm not sure how portable offsetof() would be though. In general if you want > > offsetof() itself is defined by C standard to be present both in > freestanding and hosted environment (and be available by stddef.h). You learn something every day! interesting (but still scary)..
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4640F0EE.2080206>