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From: dik@cwi.nl (Dik T. Winter)
Newsgroups: comp.lang.c
Subject: Re: towards a faster isdigit()
Message-ID: <3500@charon.cwi.nl>
Date: 9 May 91 02:33:53 GMT
References: <1991May8.030515.7004@twinsun.com> <20325@alice.att.com>
Sender: news@cwi.nl
Organization: CWI, Amsterdam
Lines: 13

In article <20325@alice.att.com> ark@alice.UUCP () writes:
 > In article <1991May8.030515.7004@twinsun.com> eggert@twinsun.com (Paul Eggert) writes:
 > > 	#define isdigit(c) ((unsigned)((c)-'0') < 10)
 > However, it does suggest an interesting puzzle: can you find a
 > character set that meets the ANSI C constraints (in particular,
 > the one that says that all digits are contiguous in the character
 > set) for which this macro will not work?  (Yes, I think there is one)
That is easy.  If your character set uses '5'-s complement to represent
the digits it will fail.  But the one I know that does that uses only 6 bits
for a char, so that violates another ANSI C constraint.
--
dik t. winter, cwi, amsterdam, nederland
dik@cwi.nl