WORDS_PER_PAGE
return (buf_idx + HEADER_WORDS) / WORDS_PER_PAGE;
const int first_page_words = WORDS_PER_PAGE - HEADER_WORDS;
return (buf_idx - first_page_words) % WORDS_PER_PAGE;
const int words = MIN(words_left, WORDS_PER_PAGE - page_offset);
const int words = MIN(words_left, WORDS_PER_PAGE - page_offset);