Key optimizations:
1. Mutable field operations: All FieldP hot-path methods (add, sub, mul, sqr)
now write into caller-provided output arrays instead of allocating new ones.
Thread-local IntArray(16) scratch for mulWide avoids per-mul allocation.
2. Mutable point operations: MutablePoint replaces immutable JPoint. Point
doubling/addition write into output points. Aliasing protection via
thread-local copy buffer for in-place doublePoint(out, out).
3. 4-bit windowed scalar multiplication: Processes 4 bits per iteration
(16 table entries) instead of 1 bit. Reduces point additions by ~4x.
4. Precomputed G table: Static lazy table of 16*G multiples. Generator
multiplication (signing, key creation) uses precomputed table directly.
5. Shamir's trick (mulDoubleG): Computes s*G + e*P in a single pass for
verification, eliminating the need for two separate scalar multiplications.
This roughly halves the cost of verifySchnorr.
6. Cached BIP-340 tag hashes: SHA256("BIP0340/challenge") etc. computed
once and reused, eliminating 2 SHA256 calls per verify.
7. toBytesInto: Writes directly into existing ByteArray at offset,
avoiding intermediate allocations in serialization.
https://claude.ai/code/session_01BhU63WUe9AhikZxRdw3Lpg
Claude
4d55dfcff5