Native build, less memory acess, improved hash mixing (#449)

prepare_abeobk.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+#
+#  Copyright 2023 The original authors
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+source "$HOME/.sdkman/bin/sdkman-init.sh"
+sdk use java 21.0.1-graal 1>&2
+
+# ./mvnw clean verify removes target/ and will re-trigger native image creation.
+if [ ! -f target/CalculateAverage_abeobk_image ]; then
+    NATIVE_IMAGE_OPTS="--gc=epsilon -O3 -march=native --enable-preview"
+    native-image $NATIVE_IMAGE_OPTS -cp target/average-1.0.0-SNAPSHOT.jar -o target/CalculateAverage_abeobk_image dev.morling.onebrc.CalculateAverage_abeobk
+fi