For uncompressed keys (04 || x || y), compression only needs the y parity
bit and a copy of x. The previous implementation decoded both coordinates
into field limbs, validated y²=x³+7 with 2 field muls, then re-encoded.
The new implementation reads the last byte of y (parity bit), copies the
32 x-bytes, and sets the 02/03 prefix. No IntArray allocations, no field
arithmetic, no curve validation — just byte manipulation.
For already-compressed input, returns the input unchanged.
Benchmark: pubKeyCompress 658K → 6.7M ops/s (was 4.5x slower, now 2.4x faster than native)
https://claude.ai/code/session_01BhU63WUe9AhikZxRdw3Lpg
Claude
de3808416c