Re: Pass int64

Hello,

2 Daniel Wallin:
Thanks for your sample. I am using LUA with 32 bit integers. Using your version of default_converter<int64>, I may read values as int64 in my cpp functions. Yes, this sample does not fully support __int64, but the sample is really useful for me.

2 Niki Bowe:
Thanks for your sample. This seems fully support __int64. I merged it with Daniel's sample (I use new luabind version) and the result worked for me. 
But how to check that metatable is correct? I know this does not relates to luabind, but could you please provide a sample?

Thanks,
Valery.

----- Original Message ----- 
From: Niki Bowe 
To: [email protected] 
Sent: Monday, June 01, 2009 5:33 AM
Subject: Re: [luabind] Pass int64



James Porter wrote: 
Niki Bowe wrte:
  Done correctly that is the best solution. Itll allow you to do 
arithmetic on 64 bit integers in lua.
Though there is a bit more to it than that.
lua_Number will need to be able to hold int64 values without loss.
which means youll need to either go with int64 as lua_Number (ie integer 
only lua)
or long double as lua_Number (non portable. no guarantee it can 
represent all 64 bit ints.
    
Are you sure about this? Because that would imply that Lua 5.1 doesn't 
work properly when compiled for a 64-bit platform since, by default, 
LUA_INTEGER is #defined to ptrdiff_t. That seems like something the Lua 
developers would have considered, but maybe not...

- Jim
  Lua certainly works on 64 bit platforms. 
It just doesnt do what you might expect. depending on what you expect.

The problem here is that lua_Number (by default) is set to double.
and internally lua values are represented by the following union
/*
** Union of all Lua values
*/
typedef union {
  GCObject *gc;
  void *p;
  lua_Number n;
  int b;
} Value;

Internally when you push an integer it casts it to lua_Number. (see the code for lua_pushinteger).
So if you want to be able to represent any 64 bit integer in lua you will have to do one of the things I suggested in a previous email.




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