bits_to_bits		7-bit = 6-bit + 6-bit
lost_carry		6-bit = 6-bit + 6-bit
extension		9-bit = 6-bit + 6-bit
truncation		4-bit = 6-bit + 6-bit

promote			7-bit = 4-bit + 6-bit
promote_lost_carry	6-bit = 4-bit + 6-bit
promote_extension	9-bit = 4-bit + 6-bit
promote_truncation	4-bit = 4-bit + 6-bit