package jdk.test;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.State;

import java.util.concurrent.ThreadLocalRandom;

/**
 * <pre>
 * Results on JDK9, Linux, i7-2600K CPU, JMH args: -f 1 -wi 5 -i 8 -gc true
 *
 * Benchmark                     Mode  Samples         Score  Score error  Units
 * j.t.HashBench2._hashCode     thrpt        8   8308858.217   353019.084  ops/s
 * j.t.HashBench2.hashCode0     thrpt        8   8207337.729   217048.634  ops/s
 * j.t.HashBench2.hashCode1     thrpt        8  13359572.359   345736.675  ops/s
 * j.t.HashBench2.hashCode2     thrpt        8  15310621.202   238369.017  ops/s
 * j.t.HashBench2.hashCode3     thrpt        8  17637944.829   232155.847  ops/s
 * j.t.HashBench2.hashCode3i    thrpt        8  17724181.444   509913.288  ops/s
 * j.t.HashBench2.hashCode3x    thrpt        8   8344128.432   159508.813  ops/s
 * j.t.HashBench2.hashCode4     thrpt        8  16526850.489   969549.448  ops/s
 * j.t.HashBench2.hashCode5     thrpt        8  17567765.554   917934.885  ops/s
 * j.t.HashBench2.hashCode6     thrpt        8  17705074.332   419405.652  ops/s
 * j.t.HashBench2.hashCode7     thrpt        8  18805633.563   209181.299  ops/s
 * j.t.HashBench2.hashCode8     thrpt        8  18300123.201   376681.550  ops/s
 *
 * </pre>
 */
@State(Scope.Benchmark)
public class HashBench2 {

    private final char[] buf;
    private final String master;

    public HashBench2() {
        buf = new char[128];
        for (int i = 0; i < buf.length; i++) {
            buf[i] = (char) ThreadLocalRandom.current().nextInt(1 << 16);
        }
        master = new String(buf);
    }


    @Benchmark
    public int _hashCode() {
        return new String(master).hashCode();
    }

    @Benchmark
    public int hashCode0() {
        int h = 0;
        for (char c : buf) {
            h = h * 31 + c;
        }
        return h;
    }

    @Benchmark
    public int hashCode1() {
        int h = 0;
        int i = 0;
        int l = buf.length - 1;
        while (i < l) {
            h = h * (31 * 31) +
                buf[i] * 31 +
                buf[i + 1];
            i += 2;
        }
        if (i < buf.length) {
            h = h * 31 + buf[i];
        }
        return h;
    }

    @Benchmark
    public int hashCode2() {
        int h = 0;
        int i = 0;
        int l = buf.length - 2;
        while (i < l) {
            h = h * (31 * 31 * 31) +
                buf[i] * (31 * 31) +
                buf[i + 1] * 31 +
                buf[i + 2];
            i += 3;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode3() {
        int h = 0;
        int i = 0;
        int l = buf.length - 3;
        while (i < l) {
            h = h * (31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31) +
                buf[i + 1] * (31 * 31) +
                buf[i + 2] * 31 +
                buf[i + 3];
            i += 4;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode3i() {
        int h = 0;
        int i = 0;
        int l = buf.length - 3;
        while (i < l) {
            h = h * (31 * 31 * 31 * 31) +
                buf[i++] * (31 * 31 * 31) +
                buf[i++] * (31 * 31) +
                buf[i++] * 31 +
                buf[i++];
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode3x() {
        int h = 0;
        int i = 0;
        int l = buf.length - 3;
        while (i < l) {
            h = (((h * 31 + buf[i]) * 31 + buf[i + 1]) * 31 + buf[i + 2]) * 31 + buf[i + 3];
            i += 4;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode4() {
        int h = 0;
        int i = 0;
        int l = buf.length - 4;
        while (i < l) {
            h = h * (31 * 31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31 * 31) +
                buf[i + 1] * (31 * 31 * 31) +
                buf[i + 2] * (31 * 31) +
                buf[i + 3] * 31 +
                buf[i + 4];
            i += 5;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode5() {
        int h = 0;
        int i = 0;
        int l = buf.length - 5;
        while (i < l) {
            h = h * (31 * 31 * 31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31 * 31 * 31) +
                buf[i + 1] * (31 * 31 * 31 * 31) +
                buf[i + 2] * (31 * 31 * 31) +
                buf[i + 3] * (31 * 31) +
                buf[i + 4] * 31 +
                buf[i + 5];
            i += 6;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode6() {
        int h = 0;
        int i = 0;
        int l = buf.length - 6;
        while (i < l) {
            //noinspection NumericOverflow
            h = h * (31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 1] * (31 * 31 * 31 * 31 * 31) +
                buf[i + 2] * (31 * 31 * 31 * 31) +
                buf[i + 3] * (31 * 31 * 31) +
                buf[i + 4] * (31 * 31) +
                buf[i + 5] * 31 +
                buf[i + 6];
            i += 7;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode7() {
        int h = 0;
        int i = 0;
        int l = buf.length - 7;
        while (i < l) {
            //noinspection NumericOverflow
            h = h * (31 * 31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 1] * (31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 2] * (31 * 31 * 31 * 31 * 31) +
                buf[i + 3] * (31 * 31 * 31 * 31) +
                buf[i + 4] * (31 * 31 * 31) +
                buf[i + 5] * (31 * 31) +
                buf[i + 6] * 31 +
                buf[i + 7];
            i += 8;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

    @Benchmark
    public int hashCode8() {
        int h = 0;
        int i = 0;
        int l = buf.length - 8;
        while (i < l) {
            //noinspection NumericOverflow
            h = h * (31 * 31 * 31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i] * (31 * 31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 1] * (31 * 31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 2] * (31 * 31 * 31 * 31 * 31 * 31) +
                buf[i + 3] * (31 * 31 * 31 * 31 * 31) +
                buf[i + 4] * (31 * 31 * 31 * 31) +
                buf[i + 5] * (31 * 31 * 31) +
                buf[i + 6] * (31 * 31) +
                buf[i + 7] * 31 +
                buf[i + 8];
            i += 9;
        }
        while (i < buf.length) {
            h = h * 31 + buf[i++];
        }
        return h;
    }

}