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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Fixed-point question
Date: Fri, 26 Jun 2015 21:44:04 -0700
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Xref: news.eternal-september.org comp.lang.ada:26492
Date: 2015-06-26T21:44:04-07:00
List-Id: <comp.lang.ada>

On 06/26/2015 08:00 PM, Patrick Noffke wrote:
> On Friday, June 26, 2015 at 6:13:11 PM UTC-5, qunying wrote:
>> In my test with Linux x86_64 with FSF GNAT 4.9.2
>>
>> C1 :=  14.664
>> C2 :=  17.000
>> Small :=  3.90625000000000000E-03
>> 1/180 :=  5.55555555555555556E-03
>>
>> With Jeffrey's changes I got:
>> C1 :=  14.667
>> C2 :=  18.000
>> Small :=  5.55555555555555556E-03
>> 1/180 :=  5.55555555555555556E-03
>>
> 
> So is this a bug, is the ARM not clear on what should happen here, or is it expected?

With a small of 1/180:

For C1, AFAICT, the compiler will calculate N/D exactly, getting 44/3 =
14.6666...., and then convert this to Fixed_type, getting 2640/180.

For C2, "/" for Fixed_Type is used, so N and D are converted to Fixed_Type
first. N = 0.2 = 36/180, and D = 0.013636... is closest to 2/180 = 0.0111...
(36/180)/(2/180) = 36/2 = 18.

Working out the expected result for the default small of 1/256 is left as an
exercise for the reader.

-- 
Jeff Carter
"I did not rob a bank. If I'd robbed a bank, everything
would be great. I tried to rob a bank, is what happened,
and they got me."
Take the Money and Run
139