Date: Sun, 6 Apr 2003 21:49:19 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Mikko =?utf-8?B?VHnDtmzDpGrDpHJ2aQ==?= <mbsd@pacbell.net> Cc: freebsd-hackers@freebsd.org Subject: Re: /bin/sh and BIG NUMBERS Message-ID: <20030407024918.GI28391@dan.emsphone.com> In-Reply-To: <20030406145748.O1122@atlas.home> References: <20030406190054.AA08537B404@hub.freebsd.org> <20030406213453.GB4780@wjv.com> <20030406145748.O1122@atlas.home>
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In the last episode (Apr 06), Mikko Ty?l?j?rvi said: > On Sun, 6 Apr 2003, Bill Vermillion wrote: > > On Sun, Apr 06, 2003 at 12:00 , > > > On 2003-04-05 07:06, Alex Semenyaka <alexs@ratmir.ru> wrote: > > > > I found that /bin/sh cannot handle numbers those do not fit to > > > > integer type. That is not too bad. Too bad that it just > > > > silently warps them in arithmetical operations: > > > > > > alexs@snark> /bin/sh -c 'echo $((10000000000-1))' > > > > 2147483646 > > > > Not all shells have that problem. I'm using the real KSH from AT&T > > via the ports. It's returns 999999999 quite nicely :-) > > Ksh seems to use floats for calculations, and so instead silently > drops precision when dealing with sufficiently large numbers: > > atlas% ksh93 -c 'echo $((10000000000002-1))' > 1e+13 > > Zsh uses 64 bit ints, which silently overflow, albeit at larger values > than FreeBSD's sh(1). The same goes for bash. > > Looks like shells aren't the best environment for bignum arithmetic :^) You could always rewrite libgmp as a set of shell functions :) POSIX requirements for math in shells are pretty lenient: * Only signed long integer arithmetic is required. As an extension, the shell may recognize arithmetic expressions beyond those listed. The shell may use a signed integer type with a rank larger than the rank of signed long. The shell may use a real-floating type instead of signed long as long as it does not affect the results in cases where there is no overflow. -- Dan Nelson dnelson@allantgroup.com
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