Simple SipHash16, SipHash32, and SipHash64 implementation in C (public domain)

siphash.c

/* 
 * UNLICENSE
 *
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * 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 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.
 *
 * For more information, please refer to <http://unlicense.org/>
 *
 * Note: I'm saving this mainly for myself as I've implemented this before in
 *       https://git.ari.lt/ari/vessel and I do NOT want to repeat this
 *       again :sob:
 */

#include <stdint.h>

#ifndef HMAP_C1
#define HMAP_C1 5
#endif /* HMAP_C1 */

#ifndef HMAP_C2
#define HMAP_C2 7
#endif /* HMAP_C2 */

#ifndef HMAP_VARIANT
#define HMAP_VARIANT 32 /* 32 bits should be enough */
#endif                  /* HMAP_VARIANT */

/* Begin HMAP_VARIANT helper type */

#if HMAP_VARIANT == 16
/* Use this if you really really really want small memory footprint in expense
 * of usability */
#define HMAP_TYPE     uint16_t
#define HMAP_TYPE_FMT "%u"
#elif HMAP_VARIANT == 32
/* The sane limit for most applications */
#define HMAP_TYPE     uint32_t
#define HMAP_TYPE_FMT "%u"
#elif HMAP_VARIANT == 64
/* If you know you'll be sending big responses - use this */
#define HMAP_TYPE     uint64_t
#define HMAP_TYPE_FMT "%lu"
#else
#error "Unsupported HMAP_VARIANT. Supported values are: 16, 32, 64"
#endif /* HMAP_TYPE */

#ifndef HMAP_SIPHASH_C_ROUNDS
#define HMAP_SIPHASH_C_ROUNDS 2
#endif /* HMAP_SIPHASH_C_ROUNDS */

#ifndef HMAP_SIPHASH_D_ROUNDS
#define HMAP_SIPHASH_D_ROUNDS 4
#endif /* HMAP_SIPHASH_D_ROUNDS */

/* Forcefully inlined for optimization purposes */

#define SIPHASH_ROTL(x, b) (x << b) | (x >> (64 - b))

#define SIPHASH_DOUBLE_ROUND(v0, v1, v2, v3) \
    do {                                     \
        v0 += v1;                            \
        v2 += v3;                            \
        v1 = SIPHASH_ROTL(v1, 13);           \
        v3 = SIPHASH_ROTL(v3, 16);           \
        v1 ^= v0;                            \
        v3 ^= v2;                            \
        v0 = SIPHASH_ROTL(v0, 32);           \
        v2 += v1;                            \
        v0 += v3;                            \
        v1 = SIPHASH_ROTL(v1, 17);           \
        v3 = SIPHASH_ROTL(v3, 21);           \
        v1 ^= v2;                            \
        v3 ^= v0;                            \
        v2 = SIPHASH_ROTL(v2, 32);           \
    } while (0)

#define SIPHASH_READ_LE64(p)                                           \
    (uint64_t) p[0] | ((uint64_t)p[1] << 8) | ((uint64_t)p[2] << 16) | \
        ((uint64_t)p[3] << 24) | ((uint64_t)p[4] << 32) |              \
        ((uint64_t)p[5] << 40) | ((uint64_t)p[6] << 48) |              \
        ((uint64_t)p[7] << 56)

void SipHash(const uint8_t *input,
             const uint64_t length,
             const uint64_t seeds[2],
             HMAP_TYPE *output);

/* Dynamic SipHash implementation */

void SipHash(const uint8_t *input,
             const uint64_t length,
             const uint64_t seeds[2],
             HMAP_TYPE *output) {
    uint64_t idx;

    uint64_t v0 = 0x736f6d6570736575ULL ^ seeds[0];
    uint64_t v1 = 0x646f72616e646f6dULL ^ seeds[1];
    uint64_t v2 = 0x6c7967656e657261ULL ^ seeds[0];
    uint64_t v3 = 0x7465646279746573ULL ^ seeds[1];

    const uint64_t *in_end =
        (const uint64_t *)(input + (length & ~(uint64_t)7));
    const uint8_t *in_tail = (const uint8_t *)in_end;
    uint64_t m;
    uint64_t b = ((uint64_t)length) << 56;

    while (input != (const uint8_t *)in_end) {
        m = SIPHASH_READ_LE64(input);
        input += sizeof(m);
        v3 ^= m;
        for (idx = 0; idx < HMAP_SIPHASH_C_ROUNDS; ++idx)
            SIPHASH_DOUBLE_ROUND(v0, v1, v2, v3);
        v0 ^= m;
    }

    for (idx = 0; idx < (length & 7); ++idx)
        b |= ((uint64_t)in_tail[idx]) << (8 * idx);
    v3 ^= b;
    for (idx = 0; idx < HMAP_SIPHASH_C_ROUNDS; ++idx)
        SIPHASH_DOUBLE_ROUND(v0, v1, v2, v3);
    v0 ^= b;

    v2 ^= 0xff;
    for (idx = 0; idx < HMAP_SIPHASH_D_ROUNDS; ++idx)
        SIPHASH_DOUBLE_ROUND(v0, v1, v2, v3);

#if HMAP_VARIANT == 16
    *(uint16_t *)output =
        (uint16_t)((v0 ^ v1 ^ v2 ^ v3) ^ ((v0 ^ v1 ^ v2 ^ v3) >> 16));
#elif HMAP_VARIANT == 32
    *(uint32_t *)output =
        (uint32_t)((v0 ^ v1 ^ v2 ^ v3) ^ ((v0 ^ v1 ^ v2 ^ v3) >> 32));
#elif HMAP_VARIANT == 64
    *(uint64_t *)output = (uint64_t)(v0 ^ v1 ^ v2 ^ v3);
#endif /* HMAP_VARIANT */
}

Benchmarks:

• O0: 4.79s/1mil calls
• O1: 3.69s/1mil calls
• O2: 3.60s/1mil calls
• O3: 3.27s/1mil calls