> Sadly (as I understand from similar discussions before) Lua implementation is heavily linked with ANSI C and Roberto generally not willing to introduce changes in logic that is different from ANSI C.
ANSI C usually means C89, where the division and modulo operators were implementation defined when either operand were negative. In Lua, on the other hand, these are not implementation defined. In more modern C standard, these are also not implementation defined, albeit different from Lua. So, in this particular case, Lua does not follow "ANSI" C at all.