CHashWriter that does SHA256 in-place during serialization #1567

SerializeHash used to create a memory-backed CDataStream, serialize the object (almost always a CTransaction) to it, and then feed it to SHA256. As most of the time is actually spent in allocating/deallocating the buffer, it is better to do the SHA256 in-place. That is what CHashWriter does.

On my system, in ultraprune running on a tmpfs-backed datadir, this alone reduces total CPU time spent during import of 185k blocks by 4-5%.

Nice! ACK on the code.

May need testcases, though there are currently no testcases for CDataStream with SER_GETHASH at all.

ACK, though Im interested to see what kind of improvement you see by simply removing duplicated Hash calls.

ACK

ACK