FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zcommon/cityhash.c

     // Copyright (c) 2011 Google, Inc.
     //
     // 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.
    
    /*
     * Copyright (c) 2017 by Delphix. All rights reserved.
     */
    
    #include <cityhash.h>
    
    #define HASH_K1 0xb492b66fbe98f273ULL
    #define HASH_K2 0x9ae16a3b2f90404fULL
    
    /*
     * Bitwise right rotate.  Normally this will compile to a single
     * instruction.
     */
    static inline uint64_t
    rotate(uint64_t val, int shift)
    {
            // Avoid shifting by 64: doing so yields an undefined result.
            return (shift == 0 ? val : (val >> shift) | (val << (64 - shift)));
    }
    
    static inline uint64_t
    cityhash_helper(uint64_t u, uint64_t v, uint64_t mul)
    {
            uint64_t a = (u ^ v) * mul;
            a ^= (a >> 47);
            uint64_t b = (v ^ a) * mul;
            b ^= (b >> 47);
            b *= mul;
            return (b);
    }
    
    uint64_t
    cityhash4(uint64_t w1, uint64_t w2, uint64_t w3, uint64_t w4)
    {
            uint64_t mul = HASH_K2 + 64;
            uint64_t a = w1 * HASH_K1;
            uint64_t b = w2;
            uint64_t c = w4 * mul;
            uint64_t d = w3 * HASH_K2;
            return (cityhash_helper(rotate(a + b, 43) + rotate(c, 30) + d,
                a + rotate(b + HASH_K2, 18) + c, mul));
    
    }
    
    #if defined(_KERNEL)
    EXPORT_SYMBOL(cityhash4);
    #endif

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