Man pages matching name is_sub_bitmap in section 3alleg4:

is_sub_bitmap.3alleg4.en	debian 10 / allegro4-doc
is_sub_bitmap.3alleg4.en	debian 11 / allegro4-doc
is_sub_bitmap.3alleg4.en	debian 12 / allegro4-doc
is_sub_bitmap.3alleg4.en	debian 13 / allegro4-doc