C++ convert large decimal to KDB

[davidcrossey]

Hi @ekallivrousis,

You could use the Double / Float type as per the C API Reference

Thanks for posting your query on the forums!

Kind regards,

David

[Laura]

Hi David,
To elaborate on @ekallivrousis comment, we are trying to use 128-bit floating point data type (instead of 64-bit(8 byte double) ) to support 24 decimal places instead of 16 decimals supported by double. Currently, as per C API Reference KDB+ supports 4byte(float) and 8byte(double).  Is there were way to store 128-bit floating point values ?

[rocuinneagain]

You can see an example of mapping a decimal to either a list of bytes or scaling to a double in this interface.

[ekallivrousis]

Hey rocuinneagain,

Correct me if im wrong but this is to do math in C correct? I want to do math operations in the KDB database. The c program will be just putting the data into DB

[rocuinneagain]

These are examples of using the C interface to extend the Kdb+ database.

 

Documentation is here:

https://code.kx.com/q/interfaces/using-c-functions/

It shows an example of writing a new ‘add’ function in C:

#include"k.h" 
#ifdef __cplusplus extern "C"{ #endif K add(K x,K y) { if(x->t!=-KJ||y->t!=-KJ) 
     return krr("type"); 
     return kj(x->j+y->j); } 
#ifdef __cplusplus } #endif

Then this can be used from inside a Kdb+ process:

q)add:(`add 2:(`add;2)) 
q)add[3;4] 
7

This is a possible method to add math functions for 128-bit floating point numbers inside Kdb+.

[ekallivrousis]

Thank you for the above this is a big step in right direction for us.

if we store large decimal will precision be lost when storing in kdb and querying to display on ui via java