Re: Undefined behaviour in luaL_checkversion_()

[Roberto Ierusalimschy <roberto@...>]

> I'd like to report an issue with Lua 5.2.1.
> 
> The luaL_checkversion_() function calls:
> 
> lua_tounsigned(L, -1) != (lua_Unsigned)-0x1234)
> 
> The lua_tounsigned() function boils down to lua_tounsignedx(), which then
> calls lua_number2unsigned(), which is defined as:
> 
> #define lua_number2unsigned(i,n)    ((i)=(lua_Unsigned)(n))
> 
> This type of cast is undefined behaviour - see
> http://stackoverflow.com/questions/2490600/iphone-floats-cast-to-unsigned-ints-get-set-to-0-if-they-are-negativefor
> more information.
> 
> The luaL_checkversion_() function passes on Windows but fails miserably on
> ARM chips.
> 
> One fix would be to change the define to:
> 
> #define lua_number2unsigned(i,n)    ((i)=((lua_Unsigned)(signed int)(n)))

Many thanks for the report.

-- Roberto