Date: Sat, 21 May 2016 14:55:17 -0700 From: Conrad Meyer <cem@FreeBSD.org> To: Pedro Giffuni <pfg@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r300377 - head/sys/compat/ndis Message-ID: <CAG6CVpV_3%2B%2BWqg2X23=RM942zaDkyL6fxH2YN0TXUqpPjneCOw@mail.gmail.com> In-Reply-To: <a88c14ea-ee78-54de-6142-08a561a49d98@FreeBSD.org> References: <201605211752.u4LHqiHQ031457@repo.freebsd.org> <CAG6CVpXjU3tHdar7d=xyr%2BTmffg0NrQu3q7SD=b6%2BjF=yvVr-Q@mail.gmail.com> <a88c14ea-ee78-54de-6142-08a561a49d98@FreeBSD.org>
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On Sat, May 21, 2016 at 1:40 PM, Pedro Giffuni <pfg@freebsd.org> wrote: > > > On 05/21/16 14:05, Conrad Meyer wrote: >> Won't this still return a negative integer in many cases? >> >> random(9) returns u_long, whereas this rand() routine returns 'int'. >> >> Even on architectures where long is the same size as ordinary >> integers, the range of possible results of the 'random() / 2 + 1' >> expression, before implicit cast to signed, is [1, 2^31] (inclusive). > > > According to: > sys/libkern/random.c > > The result is uniform on [0, 2^31 - 1]. Ah, I missed that. Sorry! In that case, I'm not sure why this is needed =E2=80=94 the result fits in a non-negative 2's complement signed integer. >> 2^31 is not representable by typical signed 32-bit integers, so this >> will wrap to INT_MIN. Also, I'm not sure why zero is excluded from >> the range. >> > > It is not a good reason but the zero is sometimes inconvenient: if > the value is going to be used as a multiplier in some calculation > it will basically kill the random component. Sure, but anyone using a random number as a multiplier must consider the range of the random function. They should handle rand() =3D=3D 0 (perhaps by this '/ 2 + 1' construct). I don't think that is the responsibility of a rand() function. Best, Conrad
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