package com.dream.HyperLogLog;



/**
 * 一种快速的非加密hash
 * 适用于对保密性要求不高以及不在意hash碰撞攻击的场合
 */
public class MurmurHash {

    public static int hash(Object o) {
        if (o == null) {
            return 0;
        }
        if (o instanceof Long) {
            return hashLong((Long) o);
        }
        if (o instanceof Integer) {
            return hashLong((Integer) o);
        }
        if (o instanceof Double) {
            return hashLong(Double.doubleToRawLongBits((Double) o));
        }
        if (o instanceof Float) {
            return hashLong(Float.floatToRawIntBits((Float) o));
        }
        if (o instanceof String) {
            return hash(((String) o).getBytes());
        }
        if (o instanceof byte[]) {
            return hash((byte[]) o);
        }
        return hash(o.toString());
    }

    public static int hash(byte[] data) {
        return hash(data, data.length, -1);
    }

    public static int hash(byte[] data, int seed) {
        return hash(data, data.length, seed);
    }

    public static int hash(byte[] data, int length, int seed) {
        int m = 0x5bd1e995;
        int r = 24;

        int h = seed ^ length;

        int len_4 = length >> 2;

        for (int i = 0; i < len_4; i++) {
            int i_4 = i << 2;
            int k = data[i_4 + 3];
            k = k << 8;
            k = k | (data[i_4 + 2] & 0xff);
            k = k << 8;
            k = k | (data[i_4 + 1] & 0xff);
            k = k << 8;
            k = k | (data[i_4 + 0] & 0xff);
            k *= m;
            k ^= k >>> r;
            k *= m;
            h *= m;
            h ^= k;
        }

        // avoid calculating modulo
        int len_m = len_4 << 2;
        int left = length - len_m;

        if (left != 0) {
            if (left >= 3) {
                h ^= (int) data[length - 3] << 16;
            }
            if (left >= 2) {
                h ^= (int) data[length - 2] << 8;
            }
            if (left >= 1) {
                h ^= (int) data[length - 1];
            }

            h *= m;
        }

        h ^= h >>> 13;
        h *= m;
        h ^= h >>> 15;

        return h;
    }

    public static int hashLong(long data) {
        int m = 0x5bd1e995;
        int r = 24;

        int h = 0;

        int k = (int) data * m;
        k ^= k >>> r;
        h ^= k * m;

        k = (int) (data >> 32) * m;
        k ^= k >>> r;
        h *= m;
        h ^= k * m;

        h ^= h >>> 13;
        h *= m;
        h ^= h >>> 15;

        return h;
    }

    public static long hash64(Object o) {
        if (o == null) {
            return 0l;
        } else if (o instanceof String) {
            final byte[] bytes = ((String) o).getBytes();
            return hash64(bytes, bytes.length);
        } else if (o instanceof byte[]) {
            final byte[] bytes = (byte[]) o;
            return hash64(bytes, bytes.length);
        }
        return hash64(o.toString());
    }

    // 64 bit implementation copied from here:  https://github.com/tnm/murmurhash-java

    /**
     * Generates 64 bit hash from byte array with default seed value.
     *
     * @param data   byte array to hash
     * @param length length of the array to hash
     * @return 64 bit hash of the given string
     */
    public static long hash64(final byte[] data, int length) {
        return hash64(data, length, 0xe17a1465);
    }


    /**
     * Generates 64 bit hash from byte array of the given length and seed.
     *
     * @param data   byte array to hash
     * @param length length of the array to hash
     * @param seed   initial seed value
     * @return 64 bit hash of the given array
     */
    public static long hash64(final byte[] data, int length, int seed) {
        final long m = 0xc6a4a7935bd1e995L;
        final int r = 47;

        long h = (seed & 0xffffffffl) ^ (length * m);

        int length8 = length / 8;

        for (int i = 0; i < length8; i++) {
            final int i8 = i * 8;
            long k = ((long) data[i8 + 0] & 0xff) + (((long) data[i8 + 1] & 0xff) << 8)
                    + (((long) data[i8 + 2] & 0xff) << 16) + (((long) data[i8 + 3] & 0xff) << 24)
                    + (((long) data[i8 + 4] & 0xff) << 32) + (((long) data[i8 + 5] & 0xff) << 40)
                    + (((long) data[i8 + 6] & 0xff) << 48) + (((long) data[i8 + 7] & 0xff) << 56);

            k *= m;
            k ^= k >>> r;
            k *= m;

            h ^= k;
            h *= m;
        }

        switch (length % 8) {
            case 7:
                h ^= (long) (data[(length & ~7) + 6] & 0xff) << 48;
            case 6:
                h ^= (long) (data[(length & ~7) + 5] & 0xff) << 40;
            case 5:
                h ^= (long) (data[(length & ~7) + 4] & 0xff) << 32;
            case 4:
                h ^= (long) (data[(length & ~7) + 3] & 0xff) << 24;
            case 3:
                h ^= (long) (data[(length & ~7) + 2] & 0xff) << 16;
            case 2:
                h ^= (long) (data[(length & ~7) + 1] & 0xff) << 8;
            case 1:
                h ^= (long) (data[length & ~7] & 0xff);
                h *= m;
        }
        ;

        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;

        return h;
    }
}

