NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/std/c/3202

Internet Message Format | 1992-12-14 | 1.6 KB

Path: sparky!uunet!mcsun!sun4nl!cwi.nl!dik
From: [e-mail] (Dik T. Winter)
Newsgroups: comp.std.c
Subject: Re: Is INT_MAX<<1 defined?
Message-ID: <[e-mail]>
Date: 13 Dec 92 00:29:50 GMT
References: <1992Dec1.050540 <1992Dec8.1 <[e-mail]>
Sender: [e-mail]
Organization: CWI, Amsterdam
Lines: 23

Norman Diamond discusses with [e-mail] about mathematical
bits, implementation bits, operations on values and operations on
representations.

What it comes down to is that << is not a mathematical operation, there
is nothing in mathematics that tells us that 16384 << 1 equals 32768.
So what is the meaning of:
1.  Operation on value in this case?  Where in the standard does it tell
    us that for signed (16 bit) int 16384, 16384 << 1 is 32768?  Is an
    implementation not allowed to define it as -32768?  Or whatever?
    But in all there is no definition in *mathematics* for this operation.
2.  Mathematical bits?  What's that?  Where in mathematics are bits
    defined (except in coding theory, where they are used in a completely
    different context where shifts are unheard of)?
The bottom-line is that shifting is not a mathematical concept, shifting
is a "computer science" concept.  So it makes no sense to talk about
mathematical operation on values or about mathematical bits.  When you
have shifted something the concept of a *value* is lost (except perhaps
in a computer science sense, which is not my field) and you need other
means to determine whether or not trapping is allowed.
--
dik t. winter, cwi, kruislaan 413, 1098 sj  amsterdam, nederland
home: bovenover 215, 1025 jn  amsterdam, nederland; e-mail: [e-mail]