I'm sure most will agree, the code is a lot easier to understand.

Another little hint to make the code easier to read (this one's from MISRA C).

As you wrote:
if(r_out >= RBUF_SIZE)
r_out = 0;
............

or another common method

if(r_out >= RBUF_SIZE) r_out = 0;
.................

MISRA C tells us this way is recommended as there is no confusion what the 'if' statement relates to.

if(r_out >= RBUF_SIZE)
{
r_out = 0;
}

Just a little change to the coding style can make a big difference to detecting and/or avoiding defects.