What is the standard (or best supported) big number (arbitrary precision) library for Lua?

Using lbc instead of lmapm would be easier because lbc is self-contained.

require"bc"
s=bc.pow(2,1000):tostring()
z=0
for i=1,#s do
        z=z+s:byte(i)-("0"):byte(1)
end
print(z)

I used Norman Ramsey's suggestion to solve Project Euler problem #16. I don't think it's a spoiler to say that the crux of the problem is calculating a 303 digit integer accurately.

Here are the steps I needed to install and use the library:

1. Lua needs to be built with dynamic loading enabled. I use Cygwin, but I changed PLAT in src/Makefile to be linux. The default, none, doesn't enable dynamic loading.

2. The MAMP needs to be built and installed somewhere that your C compiler can find it. I put libmapm.a in /usr/local/lib/. Next m_apm.h and m_apm_lc.h went to /usr/local/include/.

3. The makefile for lmamp needs to be altered to the correct location of the Lua and MAMP libraries. For me, that means uncommenting the second declaration of LUA, LUAINC, LUALIB, and LUABIN and editing the declaration of MAMP.

4. Finally, mapm.so needs to be placed somewhere that Lua will find it. I put it at /usr/local/lib/lua/5.1/.

Thank you all for the suggestions!

The lmapm library by Luiz Figueiredo, one of the authors of the Lua language.