Avoiding VC++ assertions when truncating values

[Ian Jirka <ianjirka@...>]

Hello,
 
I noticed when compiling LUA in 64-bit in VS 2013 (VC++ 18.00.21005.1), the compiler will generate
assertion code when it detects value truncation.
 
It is specifically the IntPoint macro that is affected.  The recommended solution (as described by the assertion) is to explicitly truncate the value before casting it to a narrower value type. 
 
The diff below worked for me, at least for the code coverage I have.
 
llimits.h:44
<#define IntPoint(p) ((unsigned int)(lu_mem)(p))
>#define IntPoint(p) (unsigned int)(((lu_mem)(p)) & UINT_MAX)
 
FWIW, the message generated by the VCRT is:
 

"Run-Time Check Failure #1 - A cast to a smaller data type has caused a loss of data.  If this was intentional, you should mask the source of the cast with the appropriate bitmask.  For example:
    char c = (I & 0xFF);
Changing the code in this way will not affect the quality of the resulting optimized code."

 
Cheers,
 
-Ian