hashers.h File Reference

#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <derive-c/structures/hashmap/murmurhash.h>

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Macros
#define	ALWAYS_COLLIDE(type)
	The worst possible hash, for testing purposes.
#define	ID(type)
#define	MURMURHASH_3_FMIx64(type)
#define	INT_HASHERS(_apply)
#define	MURMURHASH_DEFAULT_SEED   0x9747b28c
#define	STRING_SIZES(_apply)
#define	MURMURHASH_STRING_FIXED_SIZE(size)

Functions
size_t	hash_murmurhash_string (const char *str)
static size_t	hash_combine (size_t seed, size_t h)

Macro Definition Documentation

ALWAYS_COLLIDE

#define ALWAYS_COLLIDE

(

type

)

Value:

    static size_t hash_always_collide_##type(type const* key) { return 0; }

The worst possible hash, for testing purposes.

Interesting literature:

• [](https://burtleburtle.net/bob/hash/doobs.html)

Definition at line 12 of file hashers.h.

#define ALWAYS_COLLIDE(type)                                                                       \
    static size_t hash_always_collide_##type(type const* key) { return 0; }

ID

#define ID

(

type

)

Value:

    static size_t hash_id_##type(type const* key) {                                                \
        _Static_assert(sizeof(type) <= sizeof(size_t),                                             \
                       "ID hashing only supports up to size_t integers");                          \
        return (size_t)(*key);                                                                     \
    }

No hashing, just returns the integer value. For most circumstances with a key as a single integer, this is a good option.

Definition at line 17 of file hashers.h.

#define ID(type)                                                                                   \
    static size_t hash_id_##type(type const* key) {                                                \
        _Static_assert(sizeof(type) <= sizeof(size_t),                                             \
                       "ID hashing only supports up to size_t integers");                          \
        return (size_t)(*key);                                                                     \
    }

INT_HASHERS

#define INT_HASHERS

(

_apply

)

Value:

    _apply(int8_t  )        \
    _apply(int16_t )        \
    _apply(int32_t )        \
    _apply(int64_t )        \
    _apply(uint8_t )        \
    _apply(uint16_t)        \
    _apply(uint32_t)        \
    _apply(uint64_t)

Definition at line 36 of file hashers.h.

#define INT_HASHERS(_apply) \
    _apply(int8_t  )        \
    _apply(int16_t )        \
    _apply(int32_t )        \
    _apply(int64_t )        \
    _apply(uint8_t )        \
    _apply(uint16_t)        \
    _apply(uint32_t)        \
    _apply(uint64_t)

MURMURHASH_3_FMIx64

#define MURMURHASH_3_FMIx64

(

type

)

Value:

    static size_t hash_murmurhash3_##type(type const* key) {                                       \
        _Static_assert(sizeof(type) <= sizeof(uint64_t),                                           \
                       "MurmurHash3 only supports up to 64-bit integers");                         \
        return (size_t)derive_c_fmix64((uint64_t)(*key));                                          \
    }

Using MurmurHash3's finalizer for integer hashing.

Definition at line 28 of file hashers.h.

#define MURMURHASH_3_FMIx64(type)                                                                  \
    static size_t hash_murmurhash3_##type(type const* key) {                                       \
        _Static_assert(sizeof(type) <= sizeof(uint64_t),                                           \
                       "MurmurHash3 only supports up to 64-bit integers");                         \
        return (size_t)derive_c_fmix64((uint64_t)(*key));                                          \
    }

MURMURHASH_DEFAULT_SEED

#define MURMURHASH_DEFAULT_SEED   0x9747b28c

Definition at line 56 of file hashers.h.

MURMURHASH_STRING_FIXED_SIZE

#define MURMURHASH_STRING_FIXED_SIZE

(

size

)

Value:

    static size_t hash_murmurhash_string_##size(const char str[size]) {                            \
        return derive_c_murmurhash(str, size, MURMURHASH_DEFAULT_SEED);                            \
    }

Definition at line 73 of file hashers.h.

#define MURMURHASH_STRING_FIXED_SIZE(size)                                                         \
    static size_t hash_murmurhash_string_##size(const char str[size]) {                            \
        return derive_c_murmurhash(str, size, MURMURHASH_DEFAULT_SEED);                            \
    }

STRING_SIZES

#define STRING_SIZES

(

_apply

)

Value:

    _apply(1)                \
    _apply(2)                \
    _apply(3)                \
    _apply(4)                \
    _apply(5)                \
    _apply(6)                \
    _apply(7)                \
    _apply(8)

Definition at line 63 of file hashers.h.

#define STRING_SIZES(_apply) \
    _apply(1)                \
    _apply(2)                \
    _apply(3)                \
    _apply(4)                \
    _apply(5)                \
    _apply(6)                \
    _apply(7)                \
    _apply(8) // clang-format on

Function Documentation

hash_combine()

static size_t hash_combine ( size_t seed, size_t h )

inlinestatic

Examples

structures/hashmap.c.

Definition at line 83 of file hashers.h.

                                                         {
    // 0x9e3779b97f4a7c15 is 64-bit fractional part of the golden ratio;
    // “+ (seed<<6) + (seed>>2)” mixes seed’s bits
    return seed ^ (h + 0x9e3779b97f4a7c15ULL + (seed << 6) + (seed >> 2));
}

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hash_murmurhash_string()

size_t hash_murmurhash_string

(

const char *

str

)

Examples

structures/hashmap.c.

Definition at line 58 of file hashers.h.

                                               {
    return derive_c_murmurhash(str, (int)strlen(str), MURMURHASH_DEFAULT_SEED);
}

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