The rolling version of adler32 is just a wrapper around the standard
hash/adler32 when used in a non-rolling fashion, but it's inefficient as
it allocates a new hash instance for every Write(). This uses the
default version instead in the block hasher, and adds a test to verify
the result is the same as they were before. It reduces allocations by
88% and increases speed about 5%.
benchmark old ns/op new ns/op delta
BenchmarkHashFile-8 64434698 61303647 -4.86%
benchmark old MB/s new MB/s speedup
BenchmarkHashFile-8 276.65 290.78 1.05x
benchmark old allocs new allocs delta
BenchmarkHashFile-8 1238 150 -87.88%
benchmark old bytes new bytes delta
BenchmarkHashFile-8 17877363 49292 -99.72%
