#pragma once
#if defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS
// Fast, high-quality hash function for byte sequences.
//
// Provides HashBytes() for use in hash tables. Uses native-width integer
// loads and a 128-bit multiply-and-fold mixer for excellent avalanche
// properties on short byte sequences (network identifiers, addresses,
// tokens).
//
// Based on rapidhash V3 by Nicolas De Carli, which evolved from wyhash
// by Wang Yi. Both use the same core mixing primitive (MUM: multiply,
// then XOR the high and low halves of the 128-bit result).
//
// rapidhash: https://github.com/Nicoshev/rapidhash
// Copyright (C) 2025 Nicolas De Carli — MIT License
// wyhash: https://github.com/wangyi-fudan/wyhash
// Wang Yi — public domain (The Unlicense)
//
// The implementation here uses rapidhash's read strategy (native-width
// overlapping reads, optimized for short inputs) and secret constants.
// The core mixing function (rapid_mum/rapid_mix) is identical to
// wyhash's wymum/wymix.
#include <cstddef>
#include <cstdint>
#include <cstring>
#if defined(_MSC_VER)
#include <intrin.h>
#if defined(_M_X64) && !defined(_M_ARM64EC)
#pragma intrinsic(_umul128)
#endif
#endif
namespace node {
namespace hash_detail {
// 128-bit multiply, then XOR the high and low halves.
// This is the core mixing function ("rapid_mum" / "wymum").
// On 64-bit platforms with __int128, this compiles to a single
// mul instruction + shift + xor.
inline uint64_t RapidMix(uint64_t a, uint64_t b) {
#ifdef __SIZEOF_INT128__
__uint128_t r = static_cast<__uint128_t>(a) * b;
a = static_cast<uint64_t>(r);
b = static_cast<uint64_t>(r >> 64);
#elif defined(_MSC_VER) && (defined(_WIN64) || defined(_M_HYBRID_CHPE_ARM64))
#if defined(_M_X64)
a = _umul128(a, b, &b);
#else
uint64_t hi = __umulh(a, b);
a = a * b;
b = hi;
#endif
#else
// Portable 64x64 -> 128-bit multiply fallback for 32-bit platforms.
uint64_t ha = a >> 32, hb = b >> 32;
uint64_t la = static_cast<uint32_t>(a), lb = static_cast<uint32_t>(b);
uint64_t rh = ha * hb, rm0 = ha * lb, rm1 = hb * la, rl = la * lb;
uint64_t t = rl + (rm0 << 32);
uint64_t lo = t + (rm1 << 32);
uint64_t hi = rh + (rm0 >> 32) + (rm1 >> 32) + (t < rl) + (lo < t);
a = lo;
b = hi;
#endif
return a ^ b;
}
// Inline 128-bit multiply WITHOUT the final XOR (used in the
// penultimate mixing step where a and b are updated separately).
inline void RapidMum(uint64_t* a, uint64_t* b) {
#ifdef __SIZEOF_INT128__
__uint128_t r = static_cast<__uint128_t>(*a) * (*b);
*a = static_cast<uint64_t>(r);
*b = static_cast<uint64_t>(r >> 64);
#elif defined(_MSC_VER) && (defined(_WIN64) || defined(_M_HYBRID_CHPE_ARM64))
#if defined(_M_X64)
*a = _umul128(*a, *b, b);
#else
uint64_t hi = __umulh(*a, *b);
*a = (*a) * (*b);
*b = hi;
#endif
#else
uint64_t ha = *a >> 32, hb = *b >> 32;
uint64_t la = static_cast<uint32_t>(*a), lb = static_cast<uint32_t>(*b);
uint64_t rh = ha * hb, rm0 = ha * lb, rm1 = hb * la, rl = la * lb;
uint64_t t = rl + (rm0 << 32);
*a = t + (rm1 << 32);
*b = rh + (rm0 >> 32) + (rm1 >> 32) + (t < rl) + (*a < t);
#endif
}
// Read functions. The compiler optimizes small fixed-size memcpy calls
// to single load instructions — no actual byte-by-byte copy occurs.
inline uint64_t RapidRead64(const uint8_t* p) {
uint64_t v;
memcpy(&v, p, sizeof(uint64_t));
return v;
}
inline uint64_t RapidRead32(const uint8_t* p) {
uint32_t v;
memcpy(&v, p, sizeof(uint32_t));
return v;
}
// Default rapidhash secret parameters.
constexpr uint64_t kSecret[8] = {0x2d358dccaa6c78a5ULL,
0x8bb84b93962eacc9ULL,
0x4b33a62ed433d4a3ULL,
0x4d5a2da51de1aa47ULL,
0xa0761d6478bd642fULL,
0xe7037ed1a0b428dbULL,
0x90ed1765281c388cULL,
0xaaaaaaaaaaaaaaaaULL};
} // namespace hash_detail
// Hash a contiguous byte range. Optimized for short inputs (≤48 bytes)
// which is the common case for network identifiers and addresses. For
// inputs >48 bytes, falls through to a loop processing 48-byte chunks.
inline size_t HashBytes(const void* data, size_t len) {
const uint8_t* p = static_cast<const uint8_t*>(data);
// Seed initialization.
uint64_t seed = hash_detail::RapidMix(0 ^ hash_detail::kSecret[2],
hash_detail::kSecret[1]);
uint64_t a = 0;
uint64_t b = 0;
size_t i = len;
if (len <= 16) {
if (len >= 4) {
// Mix length into seed for better distribution of
// different-length inputs with shared prefixes.
seed ^= len;
if (len >= 8) {
// 8-16 bytes: two native 64-bit reads (overlapping from end).
a = hash_detail::RapidRead64(p);
b = hash_detail::RapidRead64(p + len - 8);
} else {
// 4-7 bytes: two 32-bit reads (overlapping from end).
a = hash_detail::RapidRead32(p);
b = hash_detail::RapidRead32(p + len - 4);
}
} else if (len > 0) {
// 1-3 bytes: spread bytes across two values for mixing.
a = (static_cast<uint64_t>(p[0]) << 45) | p[len - 1];
b = p[len >> 1];
} else {
a = b = 0;
}
} else if (len <= 48) {
// 17-48 bytes: process in 16-byte chunks, then read the tail.
seed = hash_detail::RapidMix(
hash_detail::RapidRead64(p) ^ hash_detail::kSecret[2],
hash_detail::RapidRead64(p + 8) ^ seed);
if (len > 32) {
seed = hash_detail::RapidMix(
hash_detail::RapidRead64(p + 16) ^ hash_detail::kSecret[2],
hash_detail::RapidRead64(p + 24) ^ seed);
}
a = hash_detail::RapidRead64(p + len - 16) ^ len;
b = hash_detail::RapidRead64(p + len - 8);
} else {
// >48 bytes: process 48-byte chunks with three parallel mix lanes.
uint64_t see1 = seed;
uint64_t see2 = seed;
do {
seed = hash_detail::RapidMix(
hash_detail::RapidRead64(p) ^ hash_detail::kSecret[0],
hash_detail::RapidRead64(p + 8) ^ seed);
see1 = hash_detail::RapidMix(
hash_detail::RapidRead64(p + 16) ^ hash_detail::kSecret[1],
hash_detail::RapidRead64(p + 24) ^ see1);
see2 = hash_detail::RapidMix(
hash_detail::RapidRead64(p + 32) ^ hash_detail::kSecret[2],
hash_detail::RapidRead64(p + 40) ^ see2);
p += 48;
i -= 48;
} while (i > 48);
seed ^= see1 ^ see2;
// Process remaining 17-48 bytes.
if (i > 16) {
seed = hash_detail::RapidMix(
hash_detail::RapidRead64(p) ^ hash_detail::kSecret[2],
hash_detail::RapidRead64(p + 8) ^ seed);
if (i > 32) {
seed = hash_detail::RapidMix(
hash_detail::RapidRead64(p + 16) ^ hash_detail::kSecret[2],
hash_detail::RapidRead64(p + 24) ^ seed);
}
}
a = hash_detail::RapidRead64(p + i - 16) ^ i;
b = hash_detail::RapidRead64(p + i - 8);
}
// Final mix.
a ^= hash_detail::kSecret[1];
b ^= seed;
hash_detail::RapidMum(&a, &b);
return static_cast<size_t>(hash_detail::RapidMix(
a ^ hash_detail::kSecret[7], b ^ hash_detail::kSecret[1] ^ len));
}
} // namespace node
#endif // defined(NODE_WANT_INTERNALS) && NODE_WANT_INTERNALS