Haval is a variable-length, variable-round one-way hash function designed by
Yuliang Zheng, Josef Pieprzyk, and Jennifer Seberry. The number of rounds can
be 3, 4, or 5, while the hash length can be 128, 160, 192, 224, or 256 bits.
Thus, there are a total of 15 different outputs. For better security, however,
this module implements the 5-round, 256-bit output.