This commit optimizes the decompressPoint subroutine, used in extracting
compressed pubkeys and performing pubkey recovery. We do so by replacing
the use of big.Int.Exp with with square-and-multiply exponentiation of
btcec's more optimized fieldVals, reducing the overall latency and
memory requirements of decompressPoint.
Instead of operating on bits of Q = (P+1)/4, the exponentiation applies
the square-and-multiply operations on full bytes of Q. Compared to the
original speedup. Compared the bit-wise version, the improvement is
roughly 10%.
A new pair fieldVal methods called Sqrt and SqrtVal are added, which
applies the square-and-multiply exponentiation using precomputed
byte-slice of the value Q.
Comparison against big.Int sqrt and SAM sqrt over bytes of Q:
benchmark old ns/op new ns/op delta
BenchmarkParseCompressedPubKey-8 35545 23119 -34.96%
benchmark old allocs new allocs delta
BenchmarkParseCompressedPubKey-8 35 6 -82.86%
benchmark old bytes new bytes delta
BenchmarkParseCompressedPubKey-8 2777 256 -90.78%
This slightly optimizes the NAF function by avoiding returning the
unused bit when there is not a carry.
It also adds a bunch of additional unit tests which I made while
debugging.
This commit contains various modifications for code and comment
consistency in the btcec package:
- Call out references at the top and reference them by their identifier in
the other comments
- Remove a TODO that no longer applies
- Add comments to the fields in the KoblitzCurve struct and reorder them
slightly
- Make comments wrap to 80
- Cleanup code that was far exceeding col 80 (only function declarations
typically do this)
- Extend block comments to use as much of the 80 cols as available
- Add a bit more explanation in a couple of places
- Update copyright year on secp256k1.go
- Fix a couple of typos in the comments
This commit converts the initialization of the constants to use a function
which panics on error instead of just ignoring the error. This is
acceptable since they are hard-coded constants and should never fail.
