Re: [Json] I-JSON Topic #5: Numbers

John Cowan <cowan@mercury.ccil.org> Wed, 21 May 2014 02:07 UTC

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Date: Tue, 20 May 2014 22:07:31 -0400
From: John Cowan <cowan@mercury.ccil.org>
To: "Manger, James" <James.H.Manger@team.telstra.com>
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Subject: Re: [Json] I-JSON Topic #5: Numbers
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Manger, James scripsit:

> Less precision than an "average" double maybe,
> but not less than you *expect* for a double.

It's the "chop to zero" that's a problem for i14y.

> The 1e-308 and 1e308 limits for full precision are a key part (and an
> expected part) of a double.

+1

> The best we can probably do is say that "an I-JSON message
> MUST NOT expect a receiver to treat an integer as the exact value
> given (distinct from integers differing by 1) if it is greater than
> 9007199254740992".

Almost.

"An I-JSON sender MUST NOT expect a receiver to treat a non-zero number
whose absolute value is greater than 1e308 or less than 1e-308
as an exact value.  Furthermore, an I-JSON sender MUST NOT expect a
receiver to treat an integer whose absolute value is greater than
9007199254740992 as an exact value."

>   {"x":123456789012345680000}
> 
>   {"y":123456789012345678901}

This is a special case of the above rules: these are both mathematically
1.2345678901234568e+20.

-- 
John Cowan          http://www.ccil.org/~cowan        cowan@ccil.org
By Elbereth and Luthien the Fair, you shall have neither the Ring nor me!
                --Frodo