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katyslemon · 8 years ago

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A Real-World need for C extension in the Ruby

I seriously want to start this relationship with you, the readership with pure honesty: I completely agree with the incredibility of C. However, before we get stuck into the detail, do you have any idea about C extension and why you should write one in 2016?

Here’s a discussion of a real-world need for a C extension in the Ruby language and how a non-C developer can get it done right.

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WHY WOULD YOU WANT TO WRITE ONE IN 2016?

There are two reasons behind it. One of them is speed and another is leverage. If there is a well defined problem and if there is a need for speed, then writing an extension can be a way to go.

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WRITING C EXTENSION….

Sharing my personal experience, writing C extension is a tough job and it an it advisable to go with FFI – don’t use it, until you have no other option. But, frankly speaking, I was scared of writing C into widely used application.

Apart from FFI, there were great options like for writing Ruby Extensions in Go, Crystal, Rust and many other languages where C bindings can be exposed. Anyways All I wanted to do is Go with C extension.

CLEAN C - RTOSC

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Considering several OSC and canonical implementations, it made me use macros and structs,which I didn’t completely understand at the time. I was about to give up and fortunately I stumbled on the rtosc library. It is consisted with two files rtosc.h and rtosc.c. Wishing the best spirit of open source, I enquired on GitHub issue and within few hours got a thoughtful and polite response -viva la internet!

This helped me to try writing a C extension and trust me I’m glad that I did.

Source Code – https://www.xavierriley.co.uk/writing-a-c-extension-for-ruby-in-2016/?utm_source=rubyweekly&utm_medium=email.

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GETTING STARTED

Open Sound Control and the fast_osc API

OSC is a binary protocol that looks similar to RPC. So the basic message might be looking something like this:

/methodname, "sif", ["This is a string", 123, 3.14]

So here you can have a look at the type of the arguments corresponds to a tag – s for a string, i for an int and for the Ruby API I decided to hide this so you do not consider about types.

>> FastOsc.encode_single_message("/foo", ["baz", 1, 2.0]) => "/foo\x00\x00\x00\x00,sif\x00\x00\x00\x00baz\x00\x00\x00\x00\x01@\x00\x00\x00"

It’s a tag string and an output array of the encoded versions.

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RUBY’S C API

Working out the type

switch(TYPE(current_arg))

Ints and Longs

case T_FIXNUM

Floats

case T_FLOAT:

To convert from Ruby to C NUM2DBL

Strings and Symbols

case T_STRING:

To convert Ruby symbols use rb_sym_to_s().

UNICODE STRINGS

I had broken Unicode strings. However it needs to be fixed so did my job this way.

string_arg = rb_str_new2(string_from_c); enc = rb_enc_find_index("UTF-8"); rb_enc_associate_index(string_arg, enc);

Ruby Time objects

Start with the object type

case T_DATA:

It means you have Ruby object and you can specifically check using

if (CLASS_OF(current_arg) == rb_cTime)

OSC TIMESTAMPS (NTP)

#define JAN_1970 2208988800.0 /* 2208988800 time from 1900 to 1970 in seconds */ uint64_t ruby_time_to_osc_timetag(VALUE rubytime) { uint64_t timetag; double floattime; uint32_t sec; uint32_t frac; switch(TYPE(rubytime)) { case T_NIL: timetag = 1; break; default: // convert Time object to ntp floattime = JAN_1970 + NUM2DBL(rb_funcall(rubytime, rb_intern("to_f"), 0)); sec = floor(floattime); frac = (uint32_t)(fmod(floattime, 1.0) * 4294967296); // * (2 ** 32) // printf("\nsec: %04x\n", sec); // printf("\nfrac: %04x\n", frac); timetag = (uint64_t)((uint64_t)sec << 32 | (uint64_t)frac); // printf("\ntimetag: %08llx\n", timetag); break; } return timetag; }