The original implementations used plain Ruby strings referenced from
instance variable (`@buf`) as buffers. We replaced those buffers by C
structure (`struct mrb_io_buf`) referenced directly from `fptr`.
The result is significant improvement of both performance and memory
consumption. Our simple benchmarks (reading `README.md` 10,000 times)
runs 5+ times faster, and `mrbtest` test suites consumes 85% less
memory.
Recent changes on `mruby-io` is preparation for this improvement.
In addition, update the documents referring `build_config.rb` which is
no longer used. The new `build_config.rb` describes the new configuration
structure in the comment.
The comment is for messages when `MRB_INT16` and `MRB_WITHOUT_FLOAT` are
specified at the same time.
The comment itself is no longer needed now that `MRB_INT16` is gone.
It is available by default in environments where `__unix__` is defined.
Other environments are enabled by defining `MRB_WITH_IO_PREAD_PWRITE`
(requires an implementation of `pread()` and `pwrite()` functions).
In any case, you can disable it by defining
`MRB_WITHOUT_IO_PREAD_PWRITE`.
Yukihiro "Matz" Matsumoto