NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part1/7340

Text File | 1996-08-05 | 2.6 KB | 55 lines

Path: sun001.spd.dsccc.com!spd!jmccarty
From: [e-mail] (Mike McCarty)
Newsgroups: comp.arch.arithmetic,comp.lang.c,comp.lang.c++
Subject: Re: Access carry flag from C
Date: 22 Feb 1996 20:00:24 GMT
Organization: DSC Communications Corporation, Plano, Texas USA
Message-ID: <4gii0o$[e-mail]>
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
NNTP-Posting-Host: aplo139.spd.dsccc.com

In article <[e-mail]>,
Tanmoy Bhattacharya <[e-mail]> wrote:
)In article <[e-mail]>
)[e-mail] (Arthur Chance) writes:
)<snip>
)   In article <[e-mail]> Franz Korntner <[e-mail]> writes:
)   > j+k will overflow when the result exceeds MAXINT
)   >
)   > Thus:  "if (j+k > MAXINT) overflow();" but the operation is undefined
)   > if the result overflows, so the expression needs rewriting to make sure
)   > this doesn't happen. The result is then "if (j>MAXINT-k) overflow();".
)
)   As we must be talking about signed ints, because unsigned can't cause
)   undefined behaviour by overflow, if k < 0, then MAXINT-k overflows.
)
)   Basically, the C *standard* is useless on things like signed overflow
)   (or word size, or what happens with right shift of -ve numbers, or
)   <insert your favourite "undefined behaviour" gripe here>). You have
)   to look carefully at each *implementation* you use. You can usually

If I recall the first post properly, no mention was made of "int" types,
but rather of fixed-point types. Not all fixed-point numeration systems
represent integers.

)Actually you are mixing up the concepts of `undefined behaviour' and
)`implementation-defined behaviour'. In the case of the former, even
)looking at the implementation documentation need not be sufficient: in
)the latter, the documentation has to tell you what happens.
)
)Cheers
)Tanmoy
)--
)[e-mail](128.165.23.46) DECNET: BETA::"[e-mail]"(1.218=1242)
)Tanmoy Bhattacharya O:T-8(MS B285)LANL,NM87545 H:#9,3000,Trinity Drive,NM87544
)Others see <gopher://yaleinfo.yale.edu:7700/00/Internet-People/internet-mail>,
)<http://alpha.acast.nova.edu/cgi-bin/inmgq.pl>or<ftp://csd4.csd.uwm.edu/pub/
)internetwork-mail-guide>. -- <http://nqcd.lanl.gov/people/tanmoy/tanmoy.html>
)fax: [phone]   voice: 1 [phone]    [ Home: 1 [phone] ]


----
char *p="char *p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);}

I don't speak for DSC.         <- They make me say that.