Attempt to index global 'bit32' (a nil value)

Lumberyard Discussion Scripting
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#1

I am attempting to read individual bits from a string of binary data. Everything works up until the point I call anything in the bit32 library. Calling this library produces the following error:


 [Error] (Script) - lua scripts/def file classes/defsymbol.lua:20: attempt to index global 'bit32' (a nil value)
---------- START STACK TRACE ----------

I am aware that this bitwise operators library was originally shipped in Lua 5.2, backported to 5.1, and removed in 5.3 (replaced with <<, &, | and the like). Since this came up as an autocomplete option in the Lua Editor (it turned what appears to be purple when I completed the method call), and the documentation points to the 5.1 reference, I am guessing that Lumberyard is using a version of Lua 5.1 that should have this library backported into it.

My question is as follows:

  • Is this library actually available in Lumberyard’s version of Lua?
    • If so, how do I access it? Is this a problem with my LUA_PATH/LUA_CPATH environment variables, or some other configuration thing?
      The only workaround I can think of so far is to make the operations myself. I already checked the 5.3 operators, and those symbols aren’t recognized.

The offending line of code that I used to test:

a = bit32.bor(1,4)
#2

Hi @Roosevelt.Boyland,

Lumberyard does indeed use Lua 5.1.1.8 as of LY 1.12. The bitwise operators are in 3rdParty\Lua\5.1.1.8-az\Lua\lbitlib.c however it looks like the default script context is not loading that library like the legacy script context did. In order to fix it you need to update dev\Code\Framework\AzCore\AzCore\Script\ScriptContext.cpp

At the top around line 29 add

LUALIB_API void lua_bitlibopen (lua_State* L);

Then around line 3616 after the luaL_openlibs(m_lua) line add this

lua_bitlibopen(m_lua);

After you recompile you can access the bitwise functions in lua like this (no need to require anything, the functions are in the global table)

local a = bxor(4)

However, I recommend taking a step back and considering not doing any binary manipulation in Lua, and instead writing a c++ component or library to do this for you, or expose your own c++ method to Lua.

#3

@petrocket Thanks for the information! After fiddling with trying to do this in pure Lua (and failing), I decided to move the related code to a C++ Gem. Hopefully this helps anyone who is trying to do this purely in Lua.