hash.h File Reference

constexpr-safe, compile-time hash algorithms for meta utilities. More...

#include <cstdint>
#include <concepts>
#include "jh/metax/char.h"

Go to the source code of this file.

Namespaces
namespace	jh::meta
	Aggregated entry point for compile-time metaprogramming utilities.

Enumerations
enum class	jh::meta::c_hash : std::uint8_t {   jh::meta::fnv1a64 = 0 , jh::meta::fnv1_64 = 1 , jh::meta::djb2 = 2 , jh::meta::sdbm = 3 ,   jh::meta::murmur64 = 4 , jh::meta::xxhash64 = 5 }
	Compile-time selectable hash algorithm tag (FNV, DJB2, SDBM, etc.). More...

Functions
template<any_char Char>
constexpr std::uint64_t	jh::meta::fnv1a64 (const Char *data, const std::uint64_t size) noexcept
	FNV-1a 64-bit hash implementation (default choice).
template<any_char Char>
constexpr std::uint64_t	jh::meta::fnv1_64 (const Char *data, const std::uint64_t size) noexcept
	FNV-1 64-bit hash (multiply before xor).
template<any_char Char>
constexpr std::uint64_t	jh::meta::djb2 (const Char *str, const std::uint64_t size) noexcept
	DJB2 hash (hash * 33 + c).
template<any_char Char>
constexpr std::uint64_t	jh::meta::sdbm (const Char *str, const std::uint64_t size) noexcept
	SDBM hash (used in several DB engines).
template<any_char Char>
constexpr std::uint64_t	jh::meta::murmur64 (const Char *data, const std::uint64_t size) noexcept
	constexpr MurmurHash-like 64-bit variant (seedless)
template<any_char Char>
constexpr std::uint64_t	jh::meta::xxhash64 (const Char *data, std::uint64_t len) noexcept
	constexpr xxHash-like 64-bit variant (seedless)
template<any_char Char>
constexpr std::uint64_t	jh::meta::hash (const c_hash algo, const Char *data, const std::uint64_t size) noexcept
	Dispatch to selected hash algorithm based on c_hash.

Detailed Description

constexpr-safe, compile-time hash algorithms for meta utilities.

Copyright

Copyright 2025 JeongHan-Bae <mastropseudo@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.

Full license: GitHub

Author

JeongHan-Bae <mastropseudo@gmail.com>

Provides a minimal set of constexpr 64-bit hash functions usable in compile-time contexts, such as type reflection, lookup maps, or consteval identifiers. All implementations avoid heap and STL dependencies.

Supported constexpr hash algorithms

• FNV-1a 64 — Simple, fast, and widely used for identifiers.
• FNV-1 64 — Variant with multiply-before-xor order.
• DJB2 — Classic string hash, small code footprint.
• SDBM — Hash from old DB engines (used by readdir, ndbm).
• Murmur64 — Seedless constexpr variant of MurmurHash3.
• xxHash64 — Deterministic constexpr-safe xxHash-like algorithm.

All hash functions accept any character type satisfying any_char, namely char, signed char, and unsigned char. These can be passed directly as const Char* without casting.

Other types, such as bool or std::byte, are not character types and must be explicitly converted via reinterpret_cast<const char*> if used for hashing. This restriction ensures semantic clarity and prevents accidental misuse of non-textual memory as string data in compile-time contexts.

For safe reinterpretation of POD objects or contiguous buffers, see jh::pod::bytes_view.

Version

1.3.x

Date

2025