Barrett todecimal

[MasterDuke17]

#330, but rebased onto feature-detection2 so mp_todecimal can be converted into a function that uses MP_HAS to selectively use the new s_mp_todecimal_fast.

[MasterDuke17]

@minad @czurnieden @sjaeckel how does this look? I'm in the process of adding tests, but I'm not sure about documentation. How much is needed and where does it go?

[minad]

Looks good! The CI should be green and we need tests. You can test against mp_toradix for random numbers.

[MasterDuke17]

@minad The two problems in travis are the same, but I'm not exactly sure how to fix them.

bn_s_mp_todecimal_fast.c:16:28: warning: implicitly declaring library function 'snprintf' with type 'int (char *, unsigned long, const char *, ...)' [-Wimplicit-function-declaration]

      int new_pos = left ? snprintf(*result, 4, "%u", mp_get_i32(number)) : snprintf(*result, 4, "%03u",

                           ^

bn_s_mp_todecimal_fast.c:16:28: note: include the header <stdio.h> or explicitly provide a declaration for 'snprintf'

However, stdio.h is already included. Some googling suggests other people have seem similar problems and it's some weird thing about different versions of header files. Do you have any suggestions?

[minad]

Snprintf should not be used.

[sjaeckel]

closed again in favor of #330