/**
 * Copyright (c) 2015 Daniel Kirchner
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * ---------------------------------------------------------------------------
 * \file dnn/src/common/hash_ct.h
 *
 * \brief compile time hash for strings
 *
 * MegEngine is Licensed under the Apache License, Version 2.0 (the "License")
 *
 * Copyright (c) 2014-2020 Megvii Inc. All rights reserved.
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or
 * implied.
 *
 * This file has been modified by Megvii ("Megvii Modifications").
 * All Megvii Modifications are Copyright (C) 2014-2019 Megvii Inc. All rights
 * reserved.
 *
 * ---------------------------------------------------------------------------
 *
 */

#pragma once
#include <cstdint>
namespace megdnn {
/*!
 * \brief compile-time XX64 hash implementation
 *
 * see https://github.com/ekpyron/xxhashct/blob/master/xxh64.hpp
 */
class XXHash64CT {
public:
    static constexpr uint64_t hash(const char* p, uint64_t len, uint64_t seed) {
        return finalize(
                (len >= 32 ? h32bytes(p, len, seed) : seed + PRIME5) + len,
                p + (len & ~0x1F), len & 0x1F);
    }

private:
    static constexpr uint64_t PRIME1 = 11400714785074694791ULL;
    static constexpr uint64_t PRIME2 = 14029467366897019727ULL;
    static constexpr uint64_t PRIME3 = 1609587929392839161ULL;
    static constexpr uint64_t PRIME4 = 9650029242287828579ULL;
    static constexpr uint64_t PRIME5 = 2870177450012600261ULL;

    static constexpr uint64_t rotl(uint64_t x, int r) {
        return ((x << r) | (x >> (64 - r)));
    }
    static constexpr uint64_t mix1(const uint64_t h, const uint64_t prime,
                                   int rshift) {
        return (h ^ (h >> rshift)) * prime;
    }
    static constexpr uint64_t mix2(const uint64_t p, const uint64_t v = 0) {
        return rotl(v + p * PRIME2, 31) * PRIME1;
    }
    static constexpr uint64_t mix3(const uint64_t h, const uint64_t v) {
        return (h ^ mix2(v)) * PRIME1 + PRIME4;
    }
#ifdef XXH64_BIG_ENDIAN
    static constexpr uint32_t endian32(const char* v) {
        return uint32_t(uint8_t(v[3])) | (uint32_t(uint8_t(v[2])) << 8) |
               (uint32_t(uint8_t(v[1])) << 16) |
               (uint32_t(uint8_t(v[0])) << 24);
    }
    static constexpr uint64_t endian64(const char* v) {
        return uint64_t(uint8_t(v[7])) | (uint64_t(uint8_t(v[6])) << 8) |
               (uint64_t(uint8_t(v[5])) << 16) |
               (uint64_t(uint8_t(v[4])) << 24) |
               (uint64_t(uint8_t(v[3])) << 32) |
               (uint64_t(uint8_t(v[2])) << 40) |
               (uint64_t(uint8_t(v[1])) << 48) |
               (uint64_t(uint8_t(v[0])) << 56);
    }
#else
    static constexpr uint32_t endian32(const char* v) {
        return uint32_t(uint8_t(v[0])) | (uint32_t(uint8_t(v[1])) << 8) |
               (uint32_t(uint8_t(v[2])) << 16) |
               (uint32_t(uint8_t(v[3])) << 24);
    }
    static constexpr uint64_t endian64(const char* v) {
        return uint64_t(uint8_t(v[0])) | (uint64_t(uint8_t(v[1])) << 8) |
               (uint64_t(uint8_t(v[2])) << 16) |
               (uint64_t(uint8_t(v[3])) << 24) |
               (uint64_t(uint8_t(v[4])) << 32) |
               (uint64_t(uint8_t(v[5])) << 40) |
               (uint64_t(uint8_t(v[6])) << 48) |
               (uint64_t(uint8_t(v[7])) << 56);
    }
#endif
    static constexpr uint64_t fetch64(const char* p, const uint64_t v = 0) {
        return mix2(endian64(p), v);
    }
    static constexpr uint64_t fetch32(const char* p) {
        return uint64_t(endian32(p)) * PRIME1;
    }
    static constexpr uint64_t fetch8(const char* p) {
        return uint8_t(*p) * PRIME5;
    }
    // clang-format off
    static constexpr uint64_t finalize (const uint64_t h, const char *p,
                                       uint64_t len) {
        return (len >= 8) ? (finalize (rotl (h ^ fetch64 (p), 27)
                    * PRIME1 + PRIME4, p + 8, len - 8)) :
            ((len >= 4) ? (finalize (rotl (h ^ fetch32 (p), 23)
                    * PRIME2 + PRIME3, p + 4, len - 4)) :
             ((len > 0) ? (finalize (rotl (h ^ fetch8 (p), 11)
                     * PRIME1, p + 1, len - 1)) :
              (mix1 (mix1 (mix1 (h, PRIME2, 33), PRIME3, 29), 1, 32))));
    }
    static constexpr uint64_t h32bytes (const char *p, uint64_t len,
                                        const uint64_t v1,const uint64_t v2,
                                        const uint64_t v3, const uint64_t v4) {
        return (len >= 32) ? h32bytes (p + 32, len - 32, fetch64 (p, v1), 
                fetch64 (p + 8, v2), fetch64 (p + 16, v3), 
                fetch64 (p + 24, v4)) :
                mix3 (mix3 (mix3 (mix3 (rotl (v1, 1) + rotl (v2, 7) + rotl (v3, 12)
                + rotl (v4, 18), v1), v2), v3), v4);
    }
    static constexpr uint64_t h32bytes (const char *p, uint64_t len, const uint64_t seed) {
        return h32bytes (p, len, seed + PRIME1 + PRIME2, seed + PRIME2, seed, seed - PRIME1);
    }
    // clang-format on
};
}  // namespace megdnn

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