secp256k1: Add benchmark for pubkey decompression.

dcrec/secp256k1/bench_test.go

@@ -185,3 +185,20 @@ func BenchmarkNonceRFC6979(b *testing.B) {
 	}
 	_ = noElideNonce
 }
+
+// BenchmarkPubKeyDecompress benchmarks how long it takes to decompress the  y
+// coordinate from a given public key x coordinate.
+func BenchmarkPubKeyDecompress(b *testing.B) {
+	// Randomly generated keypair.
+	// Private key: 9e0699c91ca1e3b7e3c9ba71eb71c89890872be97576010fe593fbf3fd57e66d
+	pubKeyX := fromHex("d2e670a19c6d753d1a6d8b20bd045df8a08fb162cf508956c31268c6d81ffdab")
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := decompressPoint(pubKeyX, false)
+		if err != nil {
+			b.Fatalf("unexpected err: %v", err)
+		}
+	}
+}