Lua

LuaJIT is fully upwards-compatible with Lua 5.1. It supports all standard Lua library functions and the full set of Lua/C API functions.

LuaJIT is also fully ABI-compatible to Lua 5.1 at the linker/dynamic loader level. This means you can compile a C module against the standard Lua headers and load the same shared library from either Lua or LuaJIT.

LuaJIT extends the standard Lua VM with new functionality and adds several extension modules. Please note this page is only about functional enhancements and not about performance enhancements, such as the optimized VM, the faster interpreter or the JIT compiler.

Extensions Modules

LuaJIT comes with several built-in extension modules:

bit.* — Bitwise operations

LuaJIT supports all bitwise operations as defined by Lua BitOp:

bit.tobit  bit.tohex  bit.bnot    bit.band bit.bor  bit.bxor
bit.lshift bit.rshift bit.arshift bit.rol  bit.ror  bit.bswap

This module is a LuaJIT built-in — you don't need to download or install Lua BitOp. The Lua BitOp site has full documentation for all Lua BitOp API functions.

Please make sure to require the module before using any of its functions:

local bit = require("bit")

An already installed Lua BitOp module is ignored by LuaJIT. This way you can use bit operations from both Lua and LuaJIT on a shared installation.

ffi.* — FFI library

The FFI library allows calling external C functions and the use of C data structures from pure Lua code.

jit.* — JIT compiler control

The functions in this module control the behavior of the JIT compiler engine.

C API extensions

LuaJIT adds some extra functions to the Lua/C API.

Enhanced Standard Library Functions

xpcall(f, err [,args...]) passes arguments

Unlike the standard implementation in Lua 5.1, xpcall() passes any arguments after the error function to the function which is called in a protected context.

loadfile() etc. handle UTF-8 source code

Non-ASCII characters are handled transparently by the Lua source code parser. This allows the use of UTF-8 characters in identifiers and strings. A UTF-8 BOM is skipped at the start of the source code.

tostring() etc. canonicalize NaN and ±Inf

All number-to-string conversions consistently convert non-finite numbers to the same strings on all platforms. NaN results in "nan", positive infinity results in "inf" and negative infinity results in "-inf".

tonumber() etc. use builtin string to number conversion

All string-to-number conversions consistently convert integer and floating-point inputs in decimal and hexadecimal on all platforms. strtod() is not used anymore, which avoids numerous problems with poor C library implementations. The builtin conversion function provides full precision according to the IEEE-754 standard, it works independently of the current locale and it supports hex floating-point numbers (e.g. 0x1.5p-3).

string.dump(f [,strip]) generates portable bytecode

An extra argument has been added to string.dump(). If set to true, 'stripped' bytecode without debug information is generated. This speeds up later bytecode loading and reduces memory usage. See also the -b command line option.

The generated bytecode is portable and can be loaded on any architecture that LuaJIT supports, independent of word size or endianess. However the bytecode compatibility versions must match. Bytecode stays compatible for dot releases (x.y.0 → x.y.1), but may change with major or minor releases (2.0 → 2.1) or between any beta release. Foreign bytecode (e.g. from Lua 5.1) is incompatible and cannot be loaded.

Enhanced PRNG for math.random()

LuaJIT uses a Tausworthe PRNG with period 2^223 to implement math.random() and math.randomseed(). The quality of the PRNG results is much superior compared to the standard Lua implementation which uses the platform-specific ANSI rand().

The PRNG generates the same sequences from the same seeds on all platforms and makes use of all bits in the seed argument. math.random() without arguments generates 52 pseudo-random bits for every call. The result is uniformly distributed between 0.0 and 1.0. It's correctly scaled up and rounded for math.random(n [,m]) to preserve uniformity.

io.* functions handle 64 bit file offsets

The file I/O functions in the standard io.* library handle 64 bit file offsets. In particular this means it's possible to open files larger than 2 Gigabytes and to reposition or obtain the current file position for offsets beyond 2 GB (fp:seek() method).

debug.* functions identify metamethods

debug.getinfo() and lua_getinfo() also return information about invoked metamethods. The namewhat field is set to "metamethod" and the name field has the name of the corresponding metamethod (e.g. "__index").

Fully Resumable VM

The LuaJIT VM is fully resumable. This means you can yield from a coroutine even across contexts, where this would not possible with the standard Lua 5.1 VM: e.g. you can yield across pcall() and xpcall(), across iterators and across metamethods.

Extensions from Lua 5.2

LuaJIT supports some language and library extensions from Lua 5.2. Features that are unlikely to break existing code are unconditionally enabled:

Other features are only enabled, if LuaJIT is built with -DLUAJIT_ENABLE_LUA52COMPAT:

Note: this provides only partial compatibility with Lua 5.2 at the language and Lua library level. LuaJIT is API+ABI-compatible with Lua 5.1, which prevents implementing features that would otherwise break the Lua/C API and ABI (e.g. _ENV).

C++ Exception Interoperability

LuaJIT has built-in support for interoperating with C++ exceptions. The available range of features depends on the target platform and the toolchain used to compile LuaJIT:

Platform Compiler Interoperability
POSIX/x64, DWARF2 unwinding GCC 4.3+ Full
Other platforms, DWARF2 unwinding GCC Limited
Windows/x64 MSVC or WinSDK Full
Windows/x86 Any No
Other platforms Other compilers No

Full interoperability means:

Limited interoperability means:

No interoperability means: