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From: Viet Le <vietlq85@gmail.com>
To: caml-list@inria.fr
Subject: [Caml-list] Float precision in OCaml
Date: Tue, 1 Aug 2017 11:47:27 +0100	[thread overview]
Message-ID: <CAG_8+G46xqrKjxf-_Go=F=bF5ROwrmu2=NWy3ddae_fqkbsX0A@mail.gmail.com> (raw)

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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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             reply	other threads:[~2017-08-01 10:47 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-01 10:47 Viet Le [this message]
2017-08-01 11:18 ` Nicolás Ojeda Bär
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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