Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!mit-eddie!uw-beaver!uw-june!entropy!dataio!bright
From: bright@dataio.Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: Floating point equality - (nf)
Message-ID: <1274@dataio.Data-IO.COM>
Date: Tue, 17-Mar-87 13:41:17 EST
Article-I.D.: dataio.1274
Posted: Tue Mar 17 13:41:17 1987
Date-Received: Thu, 19-Mar-87 01:08:33 EST
References: <4915@brl-adm.UUCP]  <16800001@qtecmuc.UUCP]
Reply-To: bright@dataio.UUCP (Walter Bright)
Organization: Data I/O - FutureNet Corp., Redmond, WA
Lines: 17

In article <16800001@qtecmuc.UUCP]  ger@qtecmuc.UUCP writes:
] I had a similar problem today, with Microsoft C 4.0 on an IBM-AT compatible.
] The compiler tries to hold the result of the floor... statement in the
] 80 bit register of the 8087 and loads just b into another 
] register for the comparison, if there is no other statement inbetween. Thus 
] the compiler compares the 80-bit value resulting from previous operations and 
] b, which is extended from 64 bit double precision to the internal 80 bit
] format, giving a!=b.
] My question: is this behaviour legal C ????
] Too much optimization in my eyes.

From a purist standpoint, I agree with you, but not from a practical one.
The code would expand considerably and would slow down a lot if the
8087 registers had to be stored and reloaded after every operation. I
think it's a tradeoff that most programmers would choose, since the
reason they are generating in-line 8087 code anyway is because they
want maximum speed.