Message Digest.
Zeros contents means uninitialized digest.
Check if digest is defined.
Check if digest is undefined.
Check if digest is initialized.
Data
http://stackoverflow.com/questions/1902340/can-a-sha-1-hash-be-all-zeroes
http://stackoverflow.com/questions/20179287/sha1-indexed-hash-table-in-d
See Implementation
Boost License 1.0.
Per Nordlöw 2018-.
Message Digest.
Zeros contents means uninitialized digest.