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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: routine for angles needed
Date: Mon, 03 Aug 2015 18:30:03 -0700
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Bartc <bc@freeuk.com> writes:
> On 03/08/2015 21:44, Keith Thompson wrote:
>> Bartc <bc@freeuk.com> writes:
>> [...]
>>> C uses binary floating point.
>> [...]
>>
>> Most (probably nearly all) C implementations use binary floating-point.
>> The standard permits other bases, which is why FLT_RADIX exists.
>>
>> Some IBM mainframe systems use base 16 -- which has most of the
>> characteristics of binary, but the precision fluctuates more depending
>> on the exponent value.  Base 10 floating-point is not unheard of.
>
> Using that knowledge, that there might be systems for which C doesn't 
> use binary FP, would you be able to say that fmod(9.0,3.33) gives 
> exactly 2.34?
>
> Probably not... Certainly you couldn't rely on it.

Certainly not.  On my system it yields
    2.339999999999999857891452847979962825775146484375
or equivalently
    0x1.2b851eb851eb8p+1

On a system where FLT_RADIX == 10 (or is a power of 10), fmod(9.0, 3.33)
probably would be exactly 2.34.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"