This Lua module written in C++ implements an userdata type for arbitrary big integers as BCD numbers. It defines the arithmetic binary operators + - / * % ^ and the unary - operator. Furthermore it implements the metamethods for the comparison operators == ~= <= < >= and >.
bcd = require "bcd"
local result = bcd.int( "1091274089731205741574315105408501238459018244") + "9837450983259878234932079584098479356329382873490537340570384"
print( result)9837450983259879326206169315304220930644488281991775799588628
The implementation is based on the paper BCD Arithmetic, a Tutorial from Douglas W. Jones from the University of Iowa. I implemented it in 2013 for the project https://github.com/Wolframe/Wolframe that is dead since summer 2014. The code is now reissued under a new licence (MIT) with the consent of the co-authors of the projects.