From: "Nicolás Ojeda Bär" <nicolas.ojeda.bar@lexifi.com>
To: Viet Le <vietlq85@gmail.com>
Cc: OCaml Mailing List <caml-list@inria.fr>
Subject: Re: [Caml-list] Float precision in OCaml
Date: Tue, 1 Aug 2017 13:18:15 +0200 [thread overview]
Message-ID: <CADK7aFNq0duKz-_+N3HTUQb4POAYKCdMjW7LB5-d0GwKpe8Vtw@mail.gmail.com> (raw)
In-Reply-To: <CAG_8+G46xqrKjxf-_Go=F=bF5ROwrmu2=NWy3ddae_fqkbsX0A@mail.gmail.com>
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Dear Viet,
I am not sure this is an issue with OCaml (as you can verify using your
favourite C compiler). Rather, I think IEEE 754 double-precision binary
floating-point numbers can only represent numbers between 10^{-308} and
10^308 with full decimal digits precision. Numbers smaller than that can
only be represented with reduced precision.
Best wishes,
Nicolas
On Tue, Aug 1, 2017 at 12:47 PM, Viet Le <vietlq85@gmail.com> wrote:
> Hi all,
>
> I'm writing a JSON parser in pure OCaml and have encountered an issue with
> small float values:
>
> 10 zeros in between
> # 1.00000000001e-312 ;;
> - : float = 1.00000000001e-312
>
> 11 zeros in between
> # 1.000000000001e-312 ;;
> - : float = 1.00000000000341e-312
>
> # 5e-324 ;;
> - : float = 4.94065645841e-324
>
>
> I haven't found precise limit, but as a rule of thumb (*not precise*),
> for a positive float value to keep its precision, it *should* not be
> smaller than 1.00000000001e-312. To use JSON as precise serializer, it
> would be necessary to preserve accuracy.
>
> I checked https://github.com/ocaml/Zarith and it supports only big int &
> quotients, not floating point.
>
> For values smaller than the limit above, should I just treat as 2 values:
> (normalized: float, exponent: float), so we will have:
>
> 5e-324 -> (5, -324)
>
> Comments and suggestions are appreciated. Thanks.
>
> --
> Kind regards,
> Viet
>
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next prev parent reply other threads:[~2017-08-01 11:18 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-01 10:47 Viet Le
2017-08-01 11:18 ` Nicolás Ojeda Bär [this message]
2017-08-01 11:25 ` Frédéric Bour
2017-08-01 11:45 ` Viet Le
2017-08-01 11:40 ` François Bobot
2017-08-01 11:42 ` Viet Le
2017-08-01 11:48 ` François Bobot
2017-08-01 12:12 ` Daniel Bünzli
2017-08-01 12:56 ` Viet Le
[not found] ` <etPan.59807b8a.db32dee.123@AirmailxGenerated.am>
2017-08-01 13:17 ` Daniel Bünzli
2017-08-01 13:57 ` Soegtrop, Michael
2017-08-01 14:07 ` Soegtrop, Michael
2017-08-01 15:48 ` Peter Thiemann
2017-08-01 17:12 ` Soegtrop, Michael
2017-08-02 7:41 ` Peter Thiemann
[not found] ` <etPan.5980c173.1234cb4.123@AirmailxGenerated.am>
2017-08-01 18:05 ` Daniel Bünzli
2017-08-02 5:46 ` Viet Le
2017-08-02 8:22 ` Soegtrop, Michael
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