Miscellaneous patches

[freddy77]

A bunch of not so related changes, mostly minor.

Remove misleading comment

get_current_time() is not used to seed random number generators.

Use time() to compute epoch time

Simplify get_current_time() function as time() is common to more systems.
Also is more portable allowing to support more systems.

Wrap C function for C++ in headers

This allows to include just C headers in C++ code.
This format is also more common.

Remove useless cast

POWERS items are already uint64_t.

Avoid hmac overflows in otp_generate

Returns OTP_ERROR instead.

Minor style changes

Use mnemonics to test otp_num_to_bytestring results.
Simply copy the pointer for base32_secret string.

Simplify otp_byte_secret computation

Avoids the complex shifts to compute output.

Do not rebuild tests if not changed

test_c and test_cpp are real target, so remove them from the phony list otherwise they get rebuild even if not changed.

Use proper C declaration for functions not taking arguments

For historic reasons without anything the functions are allows to take any argument, better state that there are no argument.

Make test.c a proper test

Returns success or error based on tests.

[tilkinsc]

Thanks for the PR. I have been on a coders block for a bit. I will review this.

[tilkinsc]

Could you synchronize your changes with the success bool with main.cpp with main.c Also, you changed up the way otp_generate() works. I am not sure on the specifics of how I implemented it (years ago). Have you done any sort of comprehensive test against the results of its generations?

Other than that, LGTM

[freddy77]

Could you synchronize your changes with the success bool with main.cpp with main.c Also, you changed up the way otp_generate() works. I am not sure on the specifics of how I implemented it (years ago). Have you done any sort of comprehensive test against the results of its generations?

Other than that, LGTM

Done the sync of the C++ test.
About otp_generate() I didn't change that much to be honest. They are more style changes and buffer checks. They may look more but no.
About the testing I did some manual testing using various websites and programs (like FreeOTP) confirming the tokens were correct. Also I used the test programs (that's why I added the checks). I doubt that I wrong change would make the tests pass.

[tilkinsc]

Lgtm I don't see any security vulnerabilities with your changes. I'm not sure about the complex bit shifts still but whatever. The code is generally nicer.