Re: [Caml-list] Float precision in OCaml

["Daniel Bünzli" <daniel.buenzli@erratique.ch>]

On 1 August 2017 at 14:56:23, Viet Le (vietlq85@gmail.com) wrote:
> Thanks Daniel and François for pointing out the RFC
> https://tools.ietf.org/html/rfc7159 and mentioning IEEE 754-2008 binary64.
> For my JSON parser I use Int64 to store integers and float to store
> decimal/floating point values. The tweak gives nice feature and helps with
> round-trip encoding/decoding.

I wouldn't do this; you'll get into interoperability problems, other parsers (e.g. JSON.parse) won't be able to read all the ints you are serialize via these Int64.t values, they will be represented unprecisely. Stick to [-2^53;2^53] for ints and use floats to represent them, this will force users of the codec to think about the problem. 

Here's what parsing 2^53+1 gives in my browser:

 JSON.parse('9007199254740993')
 9007199254740992

If you want to represent full Int64.t values in JSON choose a textual representation for it and serialize to a string.

Best, 

Daniel