The code uses two short base64-encoded strings to demonstrate the discrepancy in how base64ct handles the last character. Base64 is chosen as the point of comparison because it handles this issue correctly IMO.
The two strings:
-
Mi, which is
001100 100010, or split "on the byte,"00110010 0010. -
Mg, which is
001100 100000, or split "on the byte,"00110010 0000.
The former contains trailing bits that are non-zero, thus shouldn't be ignored, but are ignored by base64ct.
The latter has only zero-valued trailing bits, so the bits are safely ignored by both base64 and base64ct.