Ring buffer with Array + two indices mod 2N

ring_buffer.c

// Background: https://www.snellman.net/blog/archive/2016-12-13-ring-buffers/
// Variant with indices modulo 2*capacity as suggested by dizzy57 and Aristotle Pagaltzis

size_t read;
size_t write;

mask(val)  { return val % array.capacity; }
wrap(val)  { return val % (array.capacity * 2); }
inc(index) { return wrap(index + 1); }
push(val)  { assert(!full()); array[mask(write)] = val; write = inc(write); }
shift()    { assert(!empty()); ret = array[mask(read)]; read = inc(read); return ret; }
empty()    { return read == write; }
full()     { return size() == array.capacity; }
size()     { return wrap(write - read); }
free()     { return array.capacity - size(); }

// Additional operations

read(data_out, count) {
  count = min(count, size());

  run = min(count, array.capacity - mask(read));
  rem = count - run;

  memcpy(data_out, array + mask(read), run);
  memcpy(data_out + run, array, rem);
  read = wrap(read + count);

  return count;
}

write(data, count) {
  count = min(count, array.capacity - size());

  run = min(count, array.capacity - mask(write));
  rem = count - run;

  memcpy(array + mask(write), data, run);
  memcpy(array, data + run, rem);
  write = wrap(write + count);

  return count;
}

I think size() should be { return mask(write - read); }

I think size() should be { return mask(write - read); }

@HiFiPhile nope, that's why you do mod 2N in the first place, this way you could never arrive to size() == capacity()

Sorry I worked on an overwritable FIFO when the situation is more complicated, I must have mingled things....
https://github.com/hathach/tinyusb/blob/master/src/common/tusb_fifo.h