[atoponce]

From my testing with Python's base64, hashlib, and passlib.hash modules, SHA-256 prehashing and base64 encoding is only approximately one one-hundredths the total execution time of bcrypt_sha256 for a 4 KB "password". This is why slurping in the password during the initial state isn't noticeably adding to the overall execution time of password prehashing with bcrypt, and it is analogous to why PBKDF2, scrypt, and Argon2 all show constant time in execution regardless of password length- slurping in the password during initialization is a fraction of the execution time.