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From: em@dce.ie (Eamonn McManus)
Newsgroups: comp.lang.c
Subject: Re: When do you use "if ( a = b )"? (was Re: Funny mistake)
Message-ID: <calypso@dce.ie>
Date: 2 Apr 91 20:57:08 GMT
References: <15053@ganymede.inmos.co.uk> <3482@inews.intel.com> <20137@alice.att.com>
Organization: Datacode Communications Ltd, Dublin, Ireland
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ark@europa.att.com (Andrew Koenig) writes:
>It turned out that the effects differed if the subtract
>caused an overflow (call it underflow if you like) with a
>zero result.  In the first case, the test would show that
>a==0.  In the second, the condition code would show an
>overflow.  Overflow is not the same as zero, so the test
>would fail.

Was this a 1s-complement machine?  A sane 2s-complement machine can't
produce 0 on subtraction unless the numbers are equal.

,
Eamonn