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From: gwyn@brl-smoke.UUCP
Newsgroups: comp.lang.c
Subject: Re: MSC 4.0 and Floating Point problem
Message-ID: <6425@brl-smoke.ARPA>
Date: Sat, 12-Sep-87 17:11:36 EDT
Article-I.D.: brl-smok.6425
Posted: Sat Sep 12 17:11:36 1987
Date-Received: Sun, 13-Sep-87 08:50:07 EDT
References: <396@devon.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 11
Keywords: Floating

In article <396@devon.UUCP> paul@devon.UUCP (Paul Sutcliffe Jr.) writes:
>I am having trouble with math accuracy while developing a program

Welcome to the wonderful world of floating-point arithmetic!

>	result = (long)(atof(f) * (double)amount) + atol(a);

The problem is that the product is inexact (due to the nature
of floating-point), and by casting to (long) you truncate it
rather than round it to the nearest integer.  If the product
is known to be nonnegative, add 0.5 to it before casting.