package jdk.test;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.infra.Blackhole;

import java.util.concurrent.ThreadLocalRandom;

public class HashBench {

    private static final char[] buf;

    static {
        buf = new char[128];
        for (int i = 0; i < buf.length; i++) {
            buf[i] = (char) ThreadLocalRandom.current().nextInt(1 << 16);
        }
    }

    private static final String master = new String(buf);

    @Benchmark
    public void hashCode(Blackhole bh) {
        bh.consume(new String(master).hashCode());
    }

    @Benchmark
    public void hashCode0(Blackhole bh) {
        int h = 0;
        for (char c : buf) {
            h = h * 31 + c;
        }
        bh.consume(h);
    }

    @Benchmark
    public void hashCode1(Blackhole bh) {
        int h = 0;
        int i0 = 0;
        int i1 = 1;
        while (i1 < buf.length) {
            h = h * (31 * 31) + buf[i0] * 31 + buf[i1];
            i0 = i1 + 1;
            i1 = i0 + 1;
        }
        if (i0 < buf.length) {
            h = h * 31 + buf[i0];
        }
        bh.consume(h);
    }

    @Benchmark
    public void hashCode2(Blackhole bh) {
        int h = 0;
        int i0 = 0;
        int i1 = 1;
        int i2 = 2;
        while (i2 < buf.length) {
            h = h * (31 * 31 * 31) + buf[i0] * (31 * 31) + buf[i1] * 31 + buf[i2];
            i0 = i2 + 1;
            i1 = i0 + 1;
            i2 = i1 + 1;
        }
        if (i0 < buf.length) {
            h = h * 31 + buf[i0];
        }
        if (i1 < buf.length) {
            h = h * 31 + buf[i1];
        }
        bh.consume(h);
    }

    @Benchmark
    public void hashCode3(Blackhole bh) {
        int h = 0;
        int i0 = 0;
        int i1 = 1;
        int i2 = 2;
        int i3 = 3;
        while (i3 < buf.length) {
            h = h * (31 * 31 * 31 * 31) + buf[i0] * (31 * 31 * 31) + buf[i1] * (31 * 31) + buf[i2] * 31 + buf[i3];
            i0 = i3 + 1;
            i1 = i0 + 1;
            i2 = i1 + 1;
            i3 = i2 + 1;
        }
        if (i0 < buf.length) {
            h = h * 31 + buf[i0];
        }
        if (i1 < buf.length) {
            h = h * 31 + buf[i1];
        }
        if (i2 < buf.length) {
            h = h * 31 + buf[i2];
        }
        bh.consume(h);
    }

    @Benchmark
    public void hashCode3x(Blackhole bh) {
        int h = 0;
        int i0 = 0;
        int i1 = 1;
        int i2 = 2;
        int i3 = 3;
        while (i3 < buf.length) {
            h = (((((h * 31 + buf[i0]) * 31) + buf[i1]) * 31) + buf[i2]) * 31 + buf[i3];
            i0 = i3 + 1;
            i1 = i0 + 1;
            i2 = i1 + 1;
            i3 = i2 + 1;
        }
        if (i0 < buf.length) {
            h = h * 31 + buf[i0];
        }
        if (i1 < buf.length) {
            h = h * 31 + buf[i1];
        }
        if (i2 < buf.length) {
            h = h * 31 + buf[i2];
        }
        bh.consume(h);
    }
}