From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on
	ip-172-31-74-118.ec2.internal
X-Spam-Level: *
X-Spam-Status: No, score=1.0 required=3.0 tests=BAYES_20,FORGED_GMAIL_RCVD,
	FREEMAIL_FROM autolearn=no autolearn_force=no version=3.4.4
Path: eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail
From: =?UTF-8?Q?Bj=c3=b6rn_Lundin?= <b.f.lundin@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Fixed vs float and precision and conversions
Date: Wed, 8 Jul 2020 23:24:55 +0200
Organization: A noiseless patient Spider
Message-ID: <re5dj7$4fn$1@dont-email.me>
References: <re2obs$jus$1@dont-email.me>
 <756885db-118a-4d76-b90d-e547a3cabf28o@googlegroups.com>
 <re3vbb$kca$1@dont-email.me>
 <518ff68b-1017-4775-8248-c40048b4fe67o@googlegroups.com>
 <re522e$mat$1@dont-email.me> <re526r$mat$2@dont-email.me>
 <hmmh5pFj8hlU1@mid.individual.net> <re57d9$qv4$1@dont-email.me>
 <hmmov7FkvneU1@mid.individual.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Wed, 8 Jul 2020 21:24:55 -0000 (UTC)
Injection-Info: reader02.eternal-september.org; posting-host="bbc4443e166da1163e3df9d7300a854c";
	logging-data="4599"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX19SRmdzCyyC0yo/8pVbz2M/"
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:68.0)
 Gecko/20100101 Thunderbird/68.9.0
Cancel-Lock: sha1:RIb6IVClZF7CmbCZ47fSiTgdE28=
In-Reply-To: <hmmov7FkvneU1@mid.individual.net>
Content-Language: en-US
Xref: reader01.eternal-september.org comp.lang.ada:59406
List-Id: <comp.lang.ada>

Den 2020-07-08 kl. 22:34, skrev Niklas Holsti:

> 
> No, see below. You are confusing decimal (base-10) reals with binary 
> (base-2) floats.

Yes.

>> It is at least not certain that the number expressed in fixed_type is 
>> one of them in the array below.
>> And that is my real problem - I think.
> 
> 
> That is certainly true -- if you don't know anything about the Float 
> number, then you won't know much about the result of Fixed_Type'Round on 
> that Float number. If you want to be sure that the result is one of the 
> numbers in your table, you have to check.
> 

yes - I realize that


> 
> But the values in the Global_Odds table are all given with two decimals, 
> not three, so why not define Fixed_Type with delta 0.01, which avoids 
> this possible Float precision problem, as well as being more apt?

Because I wanted to express 6.5% -> 0.065 in fixed_type as well.
I think I mentioned that in a post.

Fixed_type is used generally here (in this system) instead of float, not 
only for that array.

This may have been a bad design choise though.

-- 
Björn