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From: tim@amdcad.AMD.COM (Tim Olson)
Newsgroups: comp.lang.c
Subject: Re: MSC C arithmetic
Message-ID: <17978@amdcad.AMD.COM>
Date: Thu, 20-Aug-87 12:40:42 EDT
Article-I.D.: amdcad.17978
Posted: Thu Aug 20 12:40:42 1987
Date-Received: Sat, 22-Aug-87 10:39:10 EDT
References: <8792@brl-adm.ARPA> <305@wrs.UUCP> <2042@umn-cs.UUCP>
Reply-To: tim@amdcad.UUCP (Tim Olson)
Organization: Advanced Micro Devices, Inc., Sunnyvale, Ca.
Lines: 26

In article <2042@umn-cs.UUCP> randy@umn-cs.UUCP (Randy Orrison) writes:
+-----
|Since the compiler is free to evaluate the expression in whatever order is
|wants, does that mean that it is not determined what types it will use?
|It seems to me that both of the following are legal:
|
|	repeat_cnt * units * blksiz * 16.0
|		--int--	       --double--
|		     --double--
|and
|	16.0 * blksiz * units * repeat_cnt
|	 --double--
|		 --double--
|			--double--
|
|Which we know can give different results.  Is this right? (under K&R and ANSI)
+-----
Yup.  To guarantee that the calculation is done correctly, you should
write it:

	16.0 * (double)blksiz * (double)units * (double)repeat_cnt;


	-- Tim Olson
	Advanced Micro Devices
	(tim@amdcad.amd.com)