Date: Fri, 05 Dec 2008 10:59:54 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: "Garrett Cooper" <yanefbsd@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org>, Christoph Mallon <christoph.mallon@gmx.de>, Maksim Yevmenkin <maksim.yevmenkin@gmail.com> Subject: Re: RFC: small syscons and kbd patch Message-ID: <861vwnhrhh.fsf@ds4.des.no> In-Reply-To: <7d6fde3d0812050131p2e9ac761n1c76575d3a3f5792@mail.gmail.com> (Garrett Cooper's message of "Fri, 5 Dec 2008 01:31:12 -0800") References: <bb4a86c70812021701i621fdcfjb6a58a7f5cf781d5@mail.gmail.com> <7d6fde3d0812040324y3bf0901cy1f4a6d961362c314@mail.gmail.com> <bb4a86c70812040724w43ddec15yab72920d80d879d3@mail.gmail.com> <20081205072229.GE18652@hoeg.nl> <7d6fde3d0812050034y43a70ce8i49fbba92f9c8943b@mail.gmail.com> <7d6fde3d0812050035u6e3ea930o9e093830a8608444@mail.gmail.com> <20081205084441.GA29312@owl.midgard.homeip.net> <7d6fde3d0812050050l57684eebkf14f252d78b68ec0@mail.gmail.com> <4938F036.4010600@gmx.de> <7d6fde3d0812050131p2e9ac761n1c76575d3a3f5792@mail.gmail.com>
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"Garrett Cooper" <yanefbsd@gmail.com> writes: > If you really want to split hairs, ! only negates the logic value, > whereas ~ actually negates the bits. So technically, you're not > flipping 0 to make 1 and vice versa, but instead flipping 0 to make > non-zero, etc. There is a clear distinction in hardware. He didn't say anything about flipping bits... and you're wrong, !0 is guaranteed to evaluate to 1. > The point was that !! isn't obvious at first glancing the C code. It is to an experienced C programmer. > Getting down to it I'd like to see what the compiler optimizes each > as, because I can see dumb compilers saying `!!' translates to `not, > bne =3D> set, else set, continue', whereas `? :' could be translated to > `bne, set, else set, continue'; I'm sure gcc has moved passed these > really minute details. Never try to second-guess the compiler. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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