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On 32-bit platforms Lua-5.1.x incorrectly formats integers that are
larger or equal to 2^31. For instance,

("%d"):format(2^31) --> -2147483648

This behavior is due to the fact that %d formatting rule casts
lua_Number (double) to the 32-bit signed integer (on 32-bit platform)
and it overflows. In standard "C" library this problem is addressed
with a "l" modifier. For example "%lld" would cast to a  "long long".
As it is clearly stated in the manual, Lua format function does not
support "l" modifier. Thus, this behavior is not a bug but a feature.

I think that the manual should explain in more details what
consequences this limitation leads to.

In meanwhile, if you need to format as a decimal integer a Lua number
larger than 31 bit long, use the following trick

("%.0f"):format(2^48) --> 281474976710656

Should this trick go into the FAQ?