In mruby, those methods are defined in `Integral` module.

Since mruby mixes `Integer` and `Float`, integer operations have
been moved to `Integral` module.

To distinguish string keys and symbol keys.

Changes applied:

- Removing "register" keyword
- Fixing const pointer to pointer assignments
- Adding type casts to rb_malloc calls

from https://github.com/ksss/mruby-method/commit/0837a0b507a5b4cdf8a1f1039ee371cee4e3b7fb