libcxx/include/__functional/hash.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___FUNCTIONAL_HASH_H
  10 #define _LIBCPP___FUNCTIONAL_HASH_H
  11
  12 #include <__config>
  13 #include <__cstddef/nullptr_t.h>
  14 #include <__functional/unary_function.h>
  15 #include <__fwd/functional.h>
  16 #include <__type_traits/conjunction.h>
  17 #include <__type_traits/enable_if.h>
  18 #include <__type_traits/invoke.h>
  19 #include <__type_traits/is_constructible.h>
  20 #include <__type_traits/is_enum.h>
  21 #include <__type_traits/underlying_type.h>
  22 #include <__utility/pair.h>
  23 #include <__utility/swap.h>
  24 #include <cstdint>
  25 #include <cstring>
  26
  27 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  28 #  pragma GCC system_header
  29 #endif
  30
  31 _LIBCPP_BEGIN_NAMESPACE_STD
  32
  33 template <class _Size>
  34 inline _LIBCPP_HIDE_FROM_ABI _Size __loadword(const void* __p) {
  35   _Size __r;
  36   std::memcpy(&__r, __p, sizeof(__r));
  37   return __r;
  38 }
  39
  40 // We use murmur2 when size_t is 32 bits, and cityhash64 when size_t
  41 // is 64 bits.  This is because cityhash64 uses 64bit x 64bit
  42 // multiplication, which can be very slow on 32-bit systems.
  43 template <class _Size, size_t = sizeof(_Size) * __CHAR_BIT__>
  44 struct __murmur2_or_cityhash;
  45
  46 template <class _Size>
  47 struct __murmur2_or_cityhash<_Size, 32> {
  48   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  49   operator()(const void* __key, _Size __len) const {
  50     // murmur2
  51     const _Size __m             = 0x5bd1e995;
  52     const _Size __r             = 24;
  53     _Size __h                   = __len;
  54     const unsigned char* __data = static_cast<const unsigned char*>(__key);
  55     for (; __len >= 4; __data += 4, __len -= 4) {
  56       _Size __k = std::__loadword<_Size>(__data);
  57       __k *= __m;
  58       __k ^= __k >> __r;
  59       __k *= __m;
  60       __h *= __m;
  61       __h ^= __k;
  62     }
  63     switch (__len) {
  64     case 3:
  65       __h ^= static_cast<_Size>(__data[2] << 16);
  66       _LIBCPP_FALLTHROUGH();
  67     case 2:
  68       __h ^= static_cast<_Size>(__data[1] << 8);
  69       _LIBCPP_FALLTHROUGH();
  70     case 1:
  71       __h ^= __data[0];
  72       __h *= __m;
  73     }
  74     __h ^= __h >> 13;
  75     __h *= __m;
  76     __h ^= __h >> 15;
  77     return __h;
  78   }
  79 };
  80
  81 template <class _Size>
  82 struct __murmur2_or_cityhash<_Size, 64> {
  83   // cityhash64
  84   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  85   operator()(const void* __key, _Size __len) const {
  86     const char* __s = static_cast<const char*>(__key);
  87     if (__len <= 32) {
  88       if (__len <= 16) {
  89         return __hash_len_0_to_16(__s, __len);
  90       } else {
  91         return __hash_len_17_to_32(__s, __len);
  92       }
  93     } else if (__len <= 64) {
  94       return __hash_len_33_to_64(__s, __len);
  95     }
  96
  97     // For strings over 64 bytes we hash the end first, and then as we
  98     // loop we keep 56 bytes of state: v, w, x, y, and z.
  99     _Size __x = std::__loadword<_Size>(__s + __len - 40);
 100     _Size __y = std::__loadword<_Size>(__s + __len - 16) + std::__loadword<_Size>(__s + __len - 56);
 101     _Size __z =
 102         __hash_len_16(std::__loadword<_Size>(__s + __len - 48) + __len, std::__loadword<_Size>(__s + __len - 24));
 103     pair<_Size, _Size> __v = __weak_hash_len_32_with_seeds(__s + __len - 64, __len, __z);
 104     pair<_Size, _Size> __w = __weak_hash_len_32_with_seeds(__s + __len - 32, __y + __k1, __x);
 105     __x                    = __x * __k1 + std::__loadword<_Size>(__s);
 106
 107     // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
 108     __len = (__len - 1) & ~static_cast<_Size>(63);
 109     do {
 110       __x = __rotate(__x + __y + __v.first + std::__loadword<_Size>(__s + 8), 37) * __k1;
 111       __y = __rotate(__y + __v.second + std::__loadword<_Size>(__s + 48), 42) * __k1;
 112       __x ^= __w.second;
 113       __y += __v.first + std::__loadword<_Size>(__s + 40);
 114       __z = __rotate(__z + __w.first, 33) * __k1;
 115       __v = __weak_hash_len_32_with_seeds(__s, __v.second * __k1, __x + __w.first);
 116       __w = __weak_hash_len_32_with_seeds(__s + 32, __z + __w.second, __y + std::__loadword<_Size>(__s + 16));
 117       std::swap(__z, __x);
 118       __s += 64;
 119       __len -= 64;
 120     } while (__len != 0);
 121     return __hash_len_16(__hash_len_16(__v.first, __w.first) + __shift_mix(__y) * __k1 + __z,
 122                          __hash_len_16(__v.second, __w.second) + __x);
 123   }
 124
 125 private:
 126   // Some primes between 2^63 and 2^64.
 127   static const _Size __k0 = 0xc3a5c85c97cb3127ULL;
 128   static const _Size __k1 = 0xb492b66fbe98f273ULL;
 129   static const _Size __k2 = 0x9ae16a3b2f90404fULL;
 130   static const _Size __k3 = 0xc949d7c7509e6557ULL;
 131
 132   _LIBCPP_HIDE_FROM_ABI static _Size __rotate(_Size __val, int __shift) {
 133     return __shift == 0 ? __val : ((__val >> __shift) | (__val << (64 - __shift)));
 134   }
 135
 136   _LIBCPP_HIDE_FROM_ABI static _Size __rotate_by_at_least_1(_Size __val, int __shift) {
 137     return (__val >> __shift) | (__val << (64 - __shift));
 138   }
 139
 140   _LIBCPP_HIDE_FROM_ABI static _Size __shift_mix(_Size __val) { return __val ^ (__val >> 47); }
 141
 142   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size __hash_len_16(_Size __u, _Size __v) {
 143     const _Size __mul = 0x9ddfea08eb382d69ULL;
 144     _Size __a         = (__u ^ __v) * __mul;
 145     __a ^= (__a >> 47);
 146     _Size __b = (__v ^ __a) * __mul;
 147     __b ^= (__b >> 47);
 148     __b *= __mul;
 149     return __b;
 150   }
 151
 152   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 153   __hash_len_0_to_16(const char* __s, _Size __len) {
 154     if (__len > 8) {
 155       const _Size __a = std::__loadword<_Size>(__s);
 156       const _Size __b = std::__loadword<_Size>(__s + __len - 8);
 157       return __hash_len_16(__a, __rotate_by_at_least_1(__b + __len, __len)) ^ __b;
 158     }
 159     if (__len >= 4) {
 160       const uint32_t __a = std::__loadword<uint32_t>(__s);
 161       const uint32_t __b = std::__loadword<uint32_t>(__s + __len - 4);
 162 #ifdef _LIBCPP_ABI_FIX_CITYHASH_IMPLEMENTATION
 163       return __hash_len_16(__len + (static_cast<_Size>(__a) << 3), __b);
 164 #else
 165       return __hash_len_16(__len + (__a << 3), __b);
 166 #endif
 167     }
 168     if (__len > 0) {
 169       const unsigned char __a = static_cast<unsigned char>(__s[0]);
 170       const unsigned char __b = static_cast<unsigned char>(__s[__len >> 1]);
 171       const unsigned char __c = static_cast<unsigned char>(__s[__len - 1]);
 172       const uint32_t __y      = static_cast<uint32_t>(__a) + (static_cast<uint32_t>(__b) << 8);
 173       const uint32_t __z      = __len + (static_cast<uint32_t>(__c) << 2);
 174       return __shift_mix(__y * __k2 ^ __z * __k3) * __k2;
 175     }
 176     return __k2;
 177   }
 178
 179   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 180   __hash_len_17_to_32(const char* __s, _Size __len) {
 181     const _Size __a = std::__loadword<_Size>(__s) * __k1;
 182     const _Size __b = std::__loadword<_Size>(__s + 8);
 183     const _Size __c = std::__loadword<_Size>(__s + __len - 8) * __k2;
 184     const _Size __d = std::__loadword<_Size>(__s + __len - 16) * __k0;
 185     return __hash_len_16(
 186         __rotate(__a - __b, 43) + __rotate(__c, 30) + __d, __a + __rotate(__b ^ __k3, 20) - __c + __len);
 187   }
 188
 189   // Return a 16-byte hash for 48 bytes.  Quick and dirty.
 190   // Callers do best to use "random-looking" values for a and b.
 191   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 192   __weak_hash_len_32_with_seeds(_Size __w, _Size __x, _Size __y, _Size __z, _Size __a, _Size __b) {
 193     __a += __w;
 194     __b             = __rotate(__b + __a + __z, 21);
 195     const _Size __c = __a;
 196     __a += __x;
 197     __a += __y;
 198     __b += __rotate(__a, 44);
 199     return pair<_Size, _Size>(__a + __z, __b + __c);
 200   }
 201
 202   // Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
 203   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 204   __weak_hash_len_32_with_seeds(const char* __s, _Size __a, _Size __b) {
 205     return __weak_hash_len_32_with_seeds(
 206         std::__loadword<_Size>(__s),
 207         std::__loadword<_Size>(__s + 8),
 208         std::__loadword<_Size>(__s + 16),
 209         std::__loadword<_Size>(__s + 24),
 210         __a,
 211         __b);
 212   }
 213
 214   // Return an 8-byte hash for 33 to 64 bytes.
 215   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 216   __hash_len_33_to_64(const char* __s, size_t __len) {
 217     _Size __z = std::__loadword<_Size>(__s + 24);
 218     _Size __a = std::__loadword<_Size>(__s) + (__len + std::__loadword<_Size>(__s + __len - 16)) * __k0;
 219     _Size __b = __rotate(__a + __z, 52);
 220     _Size __c = __rotate(__a, 37);
 221     __a += std::__loadword<_Size>(__s + 8);
 222     __c += __rotate(__a, 7);
 223     __a += std::__loadword<_Size>(__s + 16);
 224     _Size __vf = __a + __z;
 225     _Size __vs = __b + __rotate(__a, 31) + __c;
 226     __a        = std::__loadword<_Size>(__s + 16) + std::__loadword<_Size>(__s + __len - 32);
 227     __z += std::__loadword<_Size>(__s + __len - 8);
 228     __b = __rotate(__a + __z, 52);
 229     __c = __rotate(__a, 37);
 230     __a += std::__loadword<_Size>(__s + __len - 24);
 231     __c += __rotate(__a, 7);
 232     __a += std::__loadword<_Size>(__s + __len - 16);
 233     _Size __wf = __a + __z;
 234     _Size __ws = __b + __rotate(__a, 31) + __c;
 235     _Size __r  = __shift_mix((__vf + __ws) * __k2 + (__wf + __vs) * __k0);
 236     return __shift_mix(__r * __k0 + __vs) * __k2;
 237   }
 238 };
 239
 240 template <class _Tp, size_t = sizeof(_Tp) / sizeof(size_t)>
 241 struct __scalar_hash;
 242
 243 template <class _Tp>
 244 struct __scalar_hash<_Tp, 0> : public __unary_function<_Tp, size_t> {
 245   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 246     union {
 247       _Tp __t;
 248       size_t __a;
 249     } __u;
 250     __u.__a = 0;
 251     __u.__t = __v;
 252     return __u.__a;
 253   }
 254 };
 255
 256 template <class _Tp>
 257 struct __scalar_hash<_Tp, 1> : public __unary_function<_Tp, size_t> {
 258   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 259     union {
 260       _Tp __t;
 261       size_t __a;
 262     } __u;
 263     __u.__t = __v;
 264     return __u.__a;
 265   }
 266 };
 267
 268 template <class _Tp>
 269 struct __scalar_hash<_Tp, 2> : public __unary_function<_Tp, size_t> {
 270   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 271     union {
 272       _Tp __t;
 273       struct {
 274         size_t __a;
 275         size_t __b;
 276       } __s;
 277     } __u;
 278     __u.__t = __v;
 279     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 280   }
 281 };
 282
 283 template <class _Tp>
 284 struct __scalar_hash<_Tp, 3> : public __unary_function<_Tp, size_t> {
 285   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 286     union {
 287       _Tp __t;
 288       struct {
 289         size_t __a;
 290         size_t __b;
 291         size_t __c;
 292       } __s;
 293     } __u;
 294     __u.__t = __v;
 295     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 296   }
 297 };
 298
 299 template <class _Tp>
 300 struct __scalar_hash<_Tp, 4> : public __unary_function<_Tp, size_t> {
 301   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 302     union {
 303       _Tp __t;
 304       struct {
 305         size_t __a;
 306         size_t __b;
 307         size_t __c;
 308         size_t __d;
 309       } __s;
 310     } __u;
 311     __u.__t = __v;
 312     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 313   }
 314 };
 315
 316 struct _PairT {
 317   size_t first;
 318   size_t second;
 319 };
 320
 321 _LIBCPP_HIDE_FROM_ABI inline size_t __hash_combine(size_t __lhs, size_t __rhs) _NOEXCEPT {
 322   typedef __scalar_hash<_PairT> _HashT;
 323   const _PairT __p = {__lhs, __rhs};
 324   return _HashT()(__p);
 325 }
 326
 327 template <class _Tp>
 328 struct _LIBCPP_TEMPLATE_VIS hash<_Tp*> : public __unary_function<_Tp*, size_t> {
 329   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp* __v) const _NOEXCEPT {
 330     union {
 331       _Tp* __t;
 332       size_t __a;
 333     } __u;
 334     __u.__t = __v;
 335     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 336   }
 337 };
 338
 339 template <>
 340 struct _LIBCPP_TEMPLATE_VIS hash<bool> : public __unary_function<bool, size_t> {
 341   _LIBCPP_HIDE_FROM_ABI size_t operator()(bool __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 342 };
 343
 344 template <>
 345 struct _LIBCPP_TEMPLATE_VIS hash<char> : public __unary_function<char, size_t> {
 346   _LIBCPP_HIDE_FROM_ABI size_t operator()(char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 347 };
 348
 349 template <>
 350 struct _LIBCPP_TEMPLATE_VIS hash<signed char> : public __unary_function<signed char, size_t> {
 351   _LIBCPP_HIDE_FROM_ABI size_t operator()(signed char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 352 };
 353
 354 template <>
 355 struct _LIBCPP_TEMPLATE_VIS hash<unsigned char> : public __unary_function<unsigned char, size_t> {
 356   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 357 };
 358
 359 #if _LIBCPP_HAS_CHAR8_T
 360 template <>
 361 struct _LIBCPP_TEMPLATE_VIS hash<char8_t> : public __unary_function<char8_t, size_t> {
 362   _LIBCPP_HIDE_FROM_ABI size_t operator()(char8_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 363 };
 364 #endif // _LIBCPP_HAS_CHAR8_T
 365
 366 template <>
 367 struct _LIBCPP_TEMPLATE_VIS hash<char16_t> : public __unary_function<char16_t, size_t> {
 368   _LIBCPP_HIDE_FROM_ABI size_t operator()(char16_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 369 };
 370
 371 template <>
 372 struct _LIBCPP_TEMPLATE_VIS hash<char32_t> : public __unary_function<char32_t, size_t> {
 373   _LIBCPP_HIDE_FROM_ABI size_t operator()(char32_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 374 };
 375
 376 #if _LIBCPP_HAS_WIDE_CHARACTERS
 377 template <>
 378 struct _LIBCPP_TEMPLATE_VIS hash<wchar_t> : public __unary_function<wchar_t, size_t> {
 379   _LIBCPP_HIDE_FROM_ABI size_t operator()(wchar_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 380 };
 381 #endif // _LIBCPP_HAS_WIDE_CHARACTERS
 382
 383 template <>
 384 struct _LIBCPP_TEMPLATE_VIS hash<short> : public __unary_function<short, size_t> {
 385   _LIBCPP_HIDE_FROM_ABI size_t operator()(short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 386 };
 387
 388 template <>
 389 struct _LIBCPP_TEMPLATE_VIS hash<unsigned short> : public __unary_function<unsigned short, size_t> {
 390   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 391 };
 392
 393 template <>
 394 struct _LIBCPP_TEMPLATE_VIS hash<int> : public __unary_function<int, size_t> {
 395   _LIBCPP_HIDE_FROM_ABI size_t operator()(int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 396 };
 397
 398 template <>
 399 struct _LIBCPP_TEMPLATE_VIS hash<unsigned int> : public __unary_function<unsigned int, size_t> {
 400   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 401 };
 402
 403 template <>
 404 struct _LIBCPP_TEMPLATE_VIS hash<long> : public __unary_function<long, size_t> {
 405   _LIBCPP_HIDE_FROM_ABI size_t operator()(long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 406 };
 407
 408 template <>
 409 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long> : public __unary_function<unsigned long, size_t> {
 410   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT {
 411     static_assert(sizeof(size_t) >= sizeof(unsigned long),
 412                   "This would be a terrible hash function on a platform where size_t is smaller than unsigned long");
 413     return static_cast<size_t>(__v);
 414   }
 415 };
 416
 417 template <>
 418 struct _LIBCPP_TEMPLATE_VIS hash<long long> : public __scalar_hash<long long> {};
 419
 420 template <>
 421 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long long> : public __scalar_hash<unsigned long long> {};
 422
 423 #if _LIBCPP_HAS_INT128
 424
 425 template <>
 426 struct _LIBCPP_TEMPLATE_VIS hash<__int128_t> : public __scalar_hash<__int128_t> {};
 427
 428 template <>
 429 struct _LIBCPP_TEMPLATE_VIS hash<__uint128_t> : public __scalar_hash<__uint128_t> {};
 430
 431 #endif
 432
 433 template <>
 434 struct _LIBCPP_TEMPLATE_VIS hash<float> : public __scalar_hash<float> {
 435   _LIBCPP_HIDE_FROM_ABI size_t operator()(float __v) const _NOEXCEPT {
 436     // -0.0 and 0.0 should return same hash
 437     if (__v == 0.0f)
 438       return 0;
 439     return __scalar_hash<float>::operator()(__v);
 440   }
 441 };
 442
 443 template <>
 444 struct _LIBCPP_TEMPLATE_VIS hash<double> : public __scalar_hash<double> {
 445   _LIBCPP_HIDE_FROM_ABI size_t operator()(double __v) const _NOEXCEPT {
 446     // -0.0 and 0.0 should return same hash
 447     if (__v == 0.0)
 448       return 0;
 449     return __scalar_hash<double>::operator()(__v);
 450   }
 451 };
 452
 453 template <>
 454 struct _LIBCPP_TEMPLATE_VIS hash<long double> : public __scalar_hash<long double> {
 455   _LIBCPP_HIDE_FROM_ABI size_t operator()(long double __v) const _NOEXCEPT {
 456     // -0.0 and 0.0 should return same hash
 457     if (__v == 0.0L)
 458       return 0;
 459 #if defined(__i386__) || (defined(__x86_64__) && defined(__ILP32__))
 460     // Zero out padding bits
 461     union {
 462       long double __t;
 463       struct {
 464         size_t __a;
 465         size_t __b;
 466         size_t __c;
 467         size_t __d;
 468       } __s;
 469     } __u;
 470     __u.__s.__a = 0;
 471     __u.__s.__b = 0;
 472     __u.__s.__c = 0;
 473     __u.__s.__d = 0;
 474     __u.__t     = __v;
 475     return __u.__s.__a ^ __u.__s.__b ^ __u.__s.__c ^ __u.__s.__d;
 476 #elif defined(__x86_64__)
 477     // Zero out padding bits
 478     union {
 479       long double __t;
 480       struct {
 481         size_t __a;
 482         size_t __b;
 483       } __s;
 484     } __u;
 485     __u.__s.__a = 0;
 486     __u.__s.__b = 0;
 487     __u.__t     = __v;
 488     return __u.__s.__a ^ __u.__s.__b;
 489 #else
 490     return __scalar_hash<long double>::operator()(__v);
 491 #endif
 492   }
 493 };
 494
 495 template <class _Tp, bool = is_enum<_Tp>::value>
 496 struct _LIBCPP_TEMPLATE_VIS __enum_hash : public __unary_function<_Tp, size_t> {
 497   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 498     typedef typename underlying_type<_Tp>::type type;
 499     return hash<type>()(static_cast<type>(__v));
 500   }
 501 };
 502 template <class _Tp>
 503 struct _LIBCPP_TEMPLATE_VIS __enum_hash<_Tp, false> {
 504   __enum_hash()                              = delete;
 505   __enum_hash(__enum_hash const&)            = delete;
 506   __enum_hash& operator=(__enum_hash const&) = delete;
 507 };
 508
 509 template <class _Tp>
 510 struct _LIBCPP_TEMPLATE_VIS hash : public __enum_hash<_Tp> {};
 511
 512 #if _LIBCPP_STD_VER >= 17
 513
 514 template <>
 515 struct _LIBCPP_TEMPLATE_VIS hash<nullptr_t> : public __unary_function<nullptr_t, size_t> {
 516   _LIBCPP_HIDE_FROM_ABI size_t operator()(nullptr_t) const _NOEXCEPT { return 662607004ull; }
 517 };
 518 #endif
 519
 520 #ifndef _LIBCPP_CXX03_LANG
 521 template <class _Key, class _Hash>
 522 using __check_hash_requirements _LIBCPP_NODEBUG =
 523     integral_constant<bool,
 524                       is_copy_constructible<_Hash>::value && is_move_constructible<_Hash>::value &&
 525                           __invokable_r<size_t, _Hash, _Key const&>::value >;
 526
 527 template <class _Key, class _Hash = hash<_Key> >
 528 using __has_enabled_hash _LIBCPP_NODEBUG =
 529     integral_constant<bool, __check_hash_requirements<_Key, _Hash>::value && is_default_constructible<_Hash>::value >;
 530
 531 #  if _LIBCPP_STD_VER >= 17
 532 template <class _Type, class>
 533 using __enable_hash_helper_imp _LIBCPP_NODEBUG = _Type;
 534
 535 template <class _Type, class... _Keys>
 536 using __enable_hash_helper _LIBCPP_NODEBUG =
 537     __enable_hash_helper_imp<_Type, __enable_if_t<__all<__has_enabled_hash<_Keys>::value...>::value> >;
 538 #  else
 539 template <class _Type, class...>
 540 using __enable_hash_helper _LIBCPP_NODEBUG = _Type;
 541 #  endif
 542
 543 #endif // !_LIBCPP_CXX03_LANG
 544
 545 _LIBCPP_END_NAMESPACE_STD
 546
 547 #endif // _LIBCPP___FUNCTIONAL_HASH_H