64-bit FNV1a Hash (Run-Time and Compile-Time)

Hash.h

/**
 * @file Hash.h
 * @author Ben Garcia ([email protected])
 * @brief Provides run-time and compile-time 64-bit FNV1a hashing for strings and data.
 * @version 1.0
 * @date 2021-06-02
 */

#pragma once

#include <cstdint>
#include <string>

typedef uint64_t hash64_t;

// FNV1a initialization parameters
constexpr hash64_t HashInitialValue = 0xCBF29CE484222325;
constexpr hash64_t HashPrime = 0x100000001B3;

/**
 * @brief Computes the 64-bit FNV1a hash of the bytes at the given pointer.
 *
 * @param data A pointer to the data to compute the hash for.
 * @param len The number of bytes from `data` to hash.
 * @return The 64-bit FNV1a hash of the bytes.
 */
inline hash64_t HashData(const void* data, const uint32_t len) {
    const char* bytes = (char*)data;
    hash64_t hash = HashInitialValue;

    for (uint32_t i = 0; i < len; ++i) {
        uint8_t value = bytes[i];
        hash = hash ^ value;
        hash *= HashPrime;
    }

    return hash;
}

/**
 * @brief Computes the 64-bit FNV1a hash of the bytes of the given string.
 *
 * @param text The string to compute the hash for.
 * @return The 64-bit FNV1a hash of the string.
 */
inline hash64_t HashString(const std::string& text) {
    return HashData(text.c_str(), (uint32_t)text.length());
}

/**
 * @brief Computes the 64-bit FNV1a hash of the given null-terminated string literal at compile time.
 *
 * @param str The null-terminated string literal to compute the hash for.
 * @param value For internal use.
 * @param iter For internal use.
 * @return The 64-bit FNV1a hash of the string.
 *
 * @note Source: https://notes.underscorediscovery.com/constexpr-fnv1a/
 */
inline constexpr hash64_t HashDataConst(const char* const str, const hash64_t value = HashInitialValue, const int iter = 0) noexcept {
    return (str[0] == '\0') ? value : HashDataConst(&str[1], (value ^ hash64_t(str[0])) * HashPrime, iter + 1);
}

/**
 * @brief Computes the 64-bit FNV1a hash of the given null-terminated string literal at compile time, leaving no trace of the original string.
 *
 * @param str The null-terminated string literal to compute the hash for.
 */
#define STRINGHASH(str) std::integral_constant<hash64_t, HashDataConst(str, HashInitialValue, 0)>::value