Value of floating in JSONValue

[Nobody via Digitalmars-d-learn]

On Thursday, 21 August 2014 at 18:53:08 UTC, nrgyzer wrote:
> Hi everyone,
>
> I'm facing a problem with the JSON functions. I've to 
> communicate
> with another PC using JSON. Here's a simple snipped which shows
> my problem:
>
> import std.json;
> import std.stdio;
> void main()
> {
> 	double d = 1.23456789;
> 	JSONValue j = d;
> 	sendToRemote(toJSON(&j));
> }
>
> My problem is that the remote PC receives 1.23457 instead of
> 1.23456789. But when I add the following:
>
> import std.json;
> import std.stdio;
> void main()
> {
> 	double d = 1.23456789;
> 	JSONValue j = d;
> 	sendToRemote(toJSON(&j));
> 	writefln("%.8f", j.floating);
> }
>
> writefln() shows me 1.23456789. So, the value is correct. I 
> think
> the problem is the default representation of any floating point
> number to string. Is there any chance I can send 1.23456789
> instead of 1.23457 to my remote PC?
>
> Note: I cannot use strings because the other PC expects a 
> numeric
> data type.

Hi, my answer will be a bit OT, and is not really an answer but:

FP precision matters "only" during processing. I don't know which 
is the context but for example if it represents a parameter you 
could try
- to encode it to a fraction representation like "1/3".
- to encode it to a fixed-point float value.
- mapping the value in the range of -1.0 to 1.0 because by 
nature, FP values are more accurate in this range.
- to use a more accurate type: send a double (more precision), 
reduce it to a float (your 6 decimals are then granted).

Note 1: still about the context, remember that this is a damn 
small delta. Does this delta is that much a concern ?

Note 2: singles (we speak about IEEE 754, 32bits right ?) are not 
always 6 decimals precision, it's 5 >>OR<< 6.