This commit modifies the writeElement function to have a "fast path" which uses type
assertions for all of the types which btcwire write so the more expensive
reflection-based binary.Write can be avoided.
Also, this changes all cases that were writing raw ShaHash (32-byte) arrays (which
requires a stack copy) instead simply passing the pointer.
The following benchmark results show the results for serializing a block header
after these changes:
Before: BenchmarkWriteBlockHeader 500000 5566 ns/op
After: BenchmarkWriteBlockHeader 1000000 991 ns/op
This is part of the ongoing effort to optimize serialization as noted in
conformal/btcd#27.
Both of these depend on the serialized bytes which are dependent on the
version field in the block/transaction. They must be independent of the
protocol version so there is no need to require it.
The functions for generating transaction and block hashes contained a few
error checks for conditions which could never fail without run-time
panics. This commit removes those superfluous checks and adds explanatory
comments.
