package com.amazonaws.samples.aesgcmsiv;

/*
 * Copyright © 2017 Coda Hale (coda.hale@gmail.com)
 *
 * 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.
 */

// An implementation of POLYVAL based on GHASH because even BoringSSL doesn't have a POLYVAL impl.
// Does its own byte-order conversion to avoid confusion.
final class Polyval {

    private static final long E = 0xe100000000000000L;
    private static final int E1 = 0xe1000000;
    private final long h0;
    private final long h1;
    private long s0;
    private long s1;

    // mulX_GHASH, basically
    Polyval(byte[] h) {
        int v3 = Bytes.getInt(h, 0);
        int v2 = Bytes.getInt(h, 4);
        int v1 = Bytes.getInt(h, 8);
        int v0 = Bytes.getInt(h, 12);

        int b = v0;
        v0 = b >>> 1;
        int c = b << 31;
        b = v1;
        v1 = (b >>> 1) | c;
        c = b << 31;
        b = v2;
        v2 = (b >>> 1) | c;
        c = b << 31;
        b = v3;
        v3 = (b >>> 1) | c;
        v0 ^= (b << 31 >> 8 & E1);

        this.h0 = ((v0 & 0xffffffffL) << 32) | (v1 & 0xffffffffL);
        this.h1 = ((v2 & 0xffffffffL) << 32) | (v3 & 0xffffffffL);
    }

    void update(byte[] b) {
        final int extra = b.length % EncryptionAESGCMSIV.AES_BLOCK_SIZE;
        for (int i = 0; i < b.length - extra; i += EncryptionAESGCMSIV.AES_BLOCK_SIZE) {
            updateBlock(b, i);
        }

        if (extra != 0) {
            final byte[] block = new byte[EncryptionAESGCMSIV.AES_BLOCK_SIZE];
            System.arraycopy(b, b.length - extra, block, 0, extra);
            updateBlock(block, 0);
        }
    }

    @SuppressWarnings("Duplicates")
    void updateBlock(byte[] b, int offset) {
        long v0 = h0;
        long v1 = h1;
        long z0 = 0;
        long z1 = 0;

        long x0 = s1 ^ Bytes.getLong(b, offset);
        long x1 = s0 ^ Bytes.getLong(b, offset + 8);

        // breaking this up into two duplicate loops is faster

        for (int i = 0; i < 64; i++) {
            long m = x1 >> 63;
            z0 ^= v0 & m;
            z1 ^= v1 & m;
            m = v1 << 63 >> 63;
            final long c = v0 & 1L;
            v0 >>>= 1;
            v1 = v1 >>> 1 | c << 63;
            v0 ^= E & m;
            x1 <<= 1;
        }

        for (int i = 64; i < 127; i++) {
            long m = x0 >> 63;
            z0 ^= v0 & m;
            z1 ^= v1 & m;
            m = v1 << 63 >> 63;
            final long c = v0 & 1L;
            v0 >>>= 1;
            v1 = v1 >>> 1 | c << 63;
            v0 ^= E & m;
            x0 <<= 1;
        }

        final long m = x0 >> 63;
        this.s0 = (z0 ^ (v0 & m));
        this.s1 = (z1 ^ (v1 & m));
    }

    void digest(byte[] d) {
        Bytes.putLong(s1, d, 0);
        Bytes.putLong(s0, d, 8);
    }
}