Date: Thu, 30 Jun 2011 13:42:08 -0400 From: David Schultz <das@FreeBSD.ORG> To: Stefan Esser <se@FreeBSD.ORG> Cc: freebsd-standards@FreeBSD.ORG Subject: Re: Fwd: [RFC] Consistent numeric range for "expr" on all architectures Message-ID: <20110630174208.GA83700@zim.MIT.EDU> In-Reply-To: <4E0CACFB.8040906@freebsd.org> References: <4E09AF8E.5010509@freebsd.org> <4E0B860E.50504@freebsd.org> <20110630164653.GA82980@zim.MIT.EDU> <4E0CACFB.8040906@freebsd.org>
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On Thu, Jun 30, 2011, Stefan Esser wrote: > Am 30.06.2011 18:46, schrieb David Schultz: > > There are two problems, however. First, the implementation > > doesn't do this: it uses intmax_t, which has platform-dependent > > width, at least in theory. Second, it sounds like POSIX doesn't > > Yes, but it seems that intmax_t is guaranteed to be at least 64bit wide. The distinction is that int64_t is always exactly 64 bits, whereas intmax_t could be wider. If the goal is to guarantee that expr's arithmetic is architecture-independent, then int64_t is a more appropriate type. (This requires a narrowing conversion and range check after strtoimax(), but the compiler should optimize it away.) > > Overflow checking is a separate concern, and one that is more > > likely to cause problems. I'd be more careful about changing the > > default behavior there, because some scripts might rely on modular > > arithmetic without overflow checks. > > You cannot portably rely in overflow, since you have no guarantee that > overflow occurs at a specific boundary. My point was that some scripts might rely on the lack of overflow checking anyway. This is a separate and potentially more problematic change. But I'm not trying to argue that it's necessarily a bad idea. > > Another thing that is likely to cause confusion is expr(1) > > behaving differently from the shell builtin, and differently from > > the shell's arithmetic. Above all else, I suggest trying to make > > everything consistent...perhaps talk to jilles@ about the shell > > side of things. > > My change in 2000 made the shell builtin do 64bit arithmetic as well (in > fact, the shell build just included the expr.y file ...). I don't know the state of the shell these days. Didn't jilles@ change the shell to do that more recently? My point here is that working to make both the shell and expr behave identically would be ideal.home | help
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