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 <__functional/invoke.h>
  14 #include <__functional/unary_function.h>
  15 #include <__fwd/hash.h>
  16 #include <__tuple/sfinae_helpers.h>
  17 #include <__type_traits/is_copy_constructible.h>
  18 #include <__type_traits/is_default_constructible.h>
  19 #include <__type_traits/is_enum.h>
  20 #include <__type_traits/is_move_constructible.h>
  21 #include <__type_traits/underlying_type.h>
  22 #include <__utility/forward.h>
  23 #include <__utility/move.h>
  24 #include <__utility/pair.h>
  25 #include <__utility/swap.h>
  26 #include <cstddef>
  27 #include <cstdint>
  28 #include <cstring>
  29 #include <limits>
  30
  31 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  32 #  pragma GCC system_header
  33 #endif
  34
  35 _LIBCPP_BEGIN_NAMESPACE_STD
  36
  37 template <class _Size>
  38 inline _LIBCPP_HIDE_FROM_ABI _Size __loadword(const void* __p) {
  39   _Size __r;
  40   std::memcpy(&__r, __p, sizeof(__r));
  41   return __r;
  42 }
  43
  44 // We use murmur2 when size_t is 32 bits, and cityhash64 when size_t
  45 // is 64 bits.  This is because cityhash64 uses 64bit x 64bit
  46 // multiplication, which can be very slow on 32-bit systems.
  47 template <class _Size, size_t = sizeof(_Size) * __CHAR_BIT__>
  48 struct __murmur2_or_cityhash;
  49
  50 template <class _Size>
  51 struct __murmur2_or_cityhash<_Size, 32> {
  52   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  53   operator()(const void* __key, _Size __len) const {
  54     // murmur2
  55     const _Size __m             = 0x5bd1e995;
  56     const _Size __r             = 24;
  57     _Size __h                   = __len;
  58     const unsigned char* __data = static_cast<const unsigned char*>(__key);
  59     for (; __len >= 4; __data += 4, __len -= 4) {
  60       _Size __k = std::__loadword<_Size>(__data);
  61       __k *= __m;
  62       __k ^= __k >> __r;
  63       __k *= __m;
  64       __h *= __m;
  65       __h ^= __k;
  66     }
  67     switch (__len) {
  68     case 3:
  69       __h ^= static_cast<_Size>(__data[2] << 16);
  70       _LIBCPP_FALLTHROUGH();
  71     case 2:
  72       __h ^= static_cast<_Size>(__data[1] << 8);
  73       _LIBCPP_FALLTHROUGH();
  74     case 1:
  75       __h ^= __data[0];
  76       __h *= __m;
  77     }
  78     __h ^= __h >> 13;
  79     __h *= __m;
  80     __h ^= __h >> 15;
  81     return __h;
  82   }
  83 };
  84
  85 template <class _Size>
  86 struct __murmur2_or_cityhash<_Size, 64> {
  87   // cityhash64
  88   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  89   operator()(const void* __key, _Size __len) const {
  90     const char* __s = static_cast<const char*>(__key);
  91     if (__len <= 32) {
  92       if (__len <= 16) {
  93         return __hash_len_0_to_16(__s, __len);
  94       } else {
  95         return __hash_len_17_to_32(__s, __len);
  96       }
  97     } else if (__len <= 64) {
  98       return __hash_len_33_to_64(__s, __len);
  99     }
 100
 101     // For strings over 64 bytes we hash the end first, and then as we
 102     // loop we keep 56 bytes of state: v, w, x, y, and z.
 103     _Size __x = std::__loadword<_Size>(__s + __len - 40);
 104     _Size __y = std::__loadword<_Size>(__s + __len - 16) + std::__loadword<_Size>(__s + __len - 56);
 105     _Size __z =
 106         __hash_len_16(std::__loadword<_Size>(__s + __len - 48) + __len, std::__loadword<_Size>(__s + __len - 24));
 107     pair<_Size, _Size> __v = __weak_hash_len_32_with_seeds(__s + __len - 64, __len, __z);
 108     pair<_Size, _Size> __w = __weak_hash_len_32_with_seeds(__s + __len - 32, __y + __k1, __x);
 109     __x                    = __x * __k1 + std::__loadword<_Size>(__s);
 110
 111     // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
 112     __len = (__len - 1) & ~static_cast<_Size>(63);
 113     do {
 114       __x = __rotate(__x + __y + __v.first + std::__loadword<_Size>(__s + 8), 37) * __k1;
 115       __y = __rotate(__y + __v.second + std::__loadword<_Size>(__s + 48), 42) * __k1;
 116       __x ^= __w.second;
 117       __y += __v.first + std::__loadword<_Size>(__s + 40);
 118       __z = __rotate(__z + __w.first, 33) * __k1;
 119       __v = __weak_hash_len_32_with_seeds(__s, __v.second * __k1, __x + __w.first);
 120       __w = __weak_hash_len_32_with_seeds(__s + 32, __z + __w.second, __y + std::__loadword<_Size>(__s + 16));
 121       std::swap(__z, __x);
 122       __s += 64;
 123       __len -= 64;
 124     } while (__len != 0);
 125     return __hash_len_16(__hash_len_16(__v.first, __w.first) + __shift_mix(__y) * __k1 + __z,
 126                          __hash_len_16(__v.second, __w.second) + __x);
 127   }
 128
 129 private:
 130   // Some primes between 2^63 and 2^64.
 131   static const _Size __k0 = 0xc3a5c85c97cb3127ULL;
 132   static const _Size __k1 = 0xb492b66fbe98f273ULL;
 133   static const _Size __k2 = 0x9ae16a3b2f90404fULL;
 134   static const _Size __k3 = 0xc949d7c7509e6557ULL;
 135
 136   _LIBCPP_HIDE_FROM_ABI static _Size __rotate(_Size __val, int __shift) {
 137     return __shift == 0 ? __val : ((__val >> __shift) | (__val << (64 - __shift)));
 138   }
 139
 140   _LIBCPP_HIDE_FROM_ABI static _Size __rotate_by_at_least_1(_Size __val, int __shift) {
 141     return (__val >> __shift) | (__val << (64 - __shift));
 142   }
 143
 144   _LIBCPP_HIDE_FROM_ABI static _Size __shift_mix(_Size __val) { return __val ^ (__val >> 47); }
 145
 146   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size __hash_len_16(_Size __u, _Size __v) {
 147     const _Size __mul = 0x9ddfea08eb382d69ULL;
 148     _Size __a         = (__u ^ __v) * __mul;
 149     __a ^= (__a >> 47);
 150     _Size __b = (__v ^ __a) * __mul;
 151     __b ^= (__b >> 47);
 152     __b *= __mul;
 153     return __b;
 154   }
 155
 156   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 157   __hash_len_0_to_16(const char* __s, _Size __len) {
 158     if (__len > 8) {
 159       const _Size __a = std::__loadword<_Size>(__s);
 160       const _Size __b = std::__loadword<_Size>(__s + __len - 8);
 161       return __hash_len_16(__a, __rotate_by_at_least_1(__b + __len, __len)) ^ __b;
 162     }
 163     if (__len >= 4) {
 164       const uint32_t __a = std::__loadword<uint32_t>(__s);
 165       const uint32_t __b = std::__loadword<uint32_t>(__s + __len - 4);
 166 #ifdef _LIBCPP_ABI_FIX_CITYHASH_IMPLEMENTATION
 167       return __hash_len_16(__len + (static_cast<_Size>(__a) << 3), __b);
 168 #else
 169       return __hash_len_16(__len + (__a << 3), __b);
 170 #endif
 171     }
 172     if (__len > 0) {
 173       const unsigned char __a = static_cast<unsigned char>(__s[0]);
 174       const unsigned char __b = static_cast<unsigned char>(__s[__len >> 1]);
 175       const unsigned char __c = static_cast<unsigned char>(__s[__len - 1]);
 176       const uint32_t __y      = static_cast<uint32_t>(__a) + (static_cast<uint32_t>(__b) << 8);
 177       const uint32_t __z      = __len + (static_cast<uint32_t>(__c) << 2);
 178       return __shift_mix(__y * __k2 ^ __z * __k3) * __k2;
 179     }
 180     return __k2;
 181   }
 182
 183   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 184   __hash_len_17_to_32(const char* __s, _Size __len) {
 185     const _Size __a = std::__loadword<_Size>(__s) * __k1;
 186     const _Size __b = std::__loadword<_Size>(__s + 8);
 187     const _Size __c = std::__loadword<_Size>(__s + __len - 8) * __k2;
 188     const _Size __d = std::__loadword<_Size>(__s + __len - 16) * __k0;
 189     return __hash_len_16(
 190         __rotate(__a - __b, 43) + __rotate(__c, 30) + __d, __a + __rotate(__b ^ __k3, 20) - __c + __len);
 191   }
 192
 193   // Return a 16-byte hash for 48 bytes.  Quick and dirty.
 194   // Callers do best to use "random-looking" values for a and b.
 195   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 196   __weak_hash_len_32_with_seeds(_Size __w, _Size __x, _Size __y, _Size __z, _Size __a, _Size __b) {
 197     __a += __w;
 198     __b             = __rotate(__b + __a + __z, 21);
 199     const _Size __c = __a;
 200     __a += __x;
 201     __a += __y;
 202     __b += __rotate(__a, 44);
 203     return pair<_Size, _Size>(__a + __z, __b + __c);
 204   }
 205
 206   // Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
 207   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 208   __weak_hash_len_32_with_seeds(const char* __s, _Size __a, _Size __b) {
 209     return __weak_hash_len_32_with_seeds(
 210         std::__loadword<_Size>(__s),
 211         std::__loadword<_Size>(__s + 8),
 212         std::__loadword<_Size>(__s + 16),
 213         std::__loadword<_Size>(__s + 24),
 214         __a,
 215         __b);
 216   }
 217
 218   // Return an 8-byte hash for 33 to 64 bytes.
 219   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 220   __hash_len_33_to_64(const char* __s, size_t __len) {
 221     _Size __z = std::__loadword<_Size>(__s + 24);
 222     _Size __a = std::__loadword<_Size>(__s) + (__len + std::__loadword<_Size>(__s + __len - 16)) * __k0;
 223     _Size __b = __rotate(__a + __z, 52);
 224     _Size __c = __rotate(__a, 37);
 225     __a += std::__loadword<_Size>(__s + 8);
 226     __c += __rotate(__a, 7);
 227     __a += std::__loadword<_Size>(__s + 16);
 228     _Size __vf = __a + __z;
 229     _Size __vs = __b + __rotate(__a, 31) + __c;
 230     __a        = std::__loadword<_Size>(__s + 16) + std::__loadword<_Size>(__s + __len - 32);
 231     __z += std::__loadword<_Size>(__s + __len - 8);
 232     __b = __rotate(__a + __z, 52);
 233     __c = __rotate(__a, 37);
 234     __a += std::__loadword<_Size>(__s + __len - 24);
 235     __c += __rotate(__a, 7);
 236     __a += std::__loadword<_Size>(__s + __len - 16);
 237     _Size __wf = __a + __z;
 238     _Size __ws = __b + __rotate(__a, 31) + __c;
 239     _Size __r  = __shift_mix((__vf + __ws) * __k2 + (__wf + __vs) * __k0);
 240     return __shift_mix(__r * __k0 + __vs) * __k2;
 241   }
 242 };
 243
 244 template <class _Tp, size_t = sizeof(_Tp) / sizeof(size_t)>
 245 struct __scalar_hash;
 246
 247 template <class _Tp>
 248 struct __scalar_hash<_Tp, 0> : public __unary_function<_Tp, size_t> {
 249   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 250     union {
 251       _Tp __t;
 252       size_t __a;
 253     } __u;
 254     __u.__a = 0;
 255     __u.__t = __v;
 256     return __u.__a;
 257   }
 258 };
 259
 260 template <class _Tp>
 261 struct __scalar_hash<_Tp, 1> : public __unary_function<_Tp, size_t> {
 262   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 263     union {
 264       _Tp __t;
 265       size_t __a;
 266     } __u;
 267     __u.__t = __v;
 268     return __u.__a;
 269   }
 270 };
 271
 272 template <class _Tp>
 273 struct __scalar_hash<_Tp, 2> : public __unary_function<_Tp, size_t> {
 274   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 275     union {
 276       _Tp __t;
 277       struct {
 278         size_t __a;
 279         size_t __b;
 280       } __s;
 281     } __u;
 282     __u.__t = __v;
 283     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 284   }
 285 };
 286
 287 template <class _Tp>
 288 struct __scalar_hash<_Tp, 3> : public __unary_function<_Tp, size_t> {
 289   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 290     union {
 291       _Tp __t;
 292       struct {
 293         size_t __a;
 294         size_t __b;
 295         size_t __c;
 296       } __s;
 297     } __u;
 298     __u.__t = __v;
 299     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 300   }
 301 };
 302
 303 template <class _Tp>
 304 struct __scalar_hash<_Tp, 4> : public __unary_function<_Tp, size_t> {
 305   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 306     union {
 307       _Tp __t;
 308       struct {
 309         size_t __a;
 310         size_t __b;
 311         size_t __c;
 312         size_t __d;
 313       } __s;
 314     } __u;
 315     __u.__t = __v;
 316     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 317   }
 318 };
 319
 320 struct _PairT {
 321   size_t first;
 322   size_t second;
 323 };
 324
 325 _LIBCPP_HIDE_FROM_ABI inline size_t __hash_combine(size_t __lhs, size_t __rhs) _NOEXCEPT {
 326   typedef __scalar_hash<_PairT> _HashT;
 327   const _PairT __p = {__lhs, __rhs};
 328   return _HashT()(__p);
 329 }
 330
 331 template <class _Tp>
 332 struct _LIBCPP_TEMPLATE_VIS hash<_Tp*> : public __unary_function<_Tp*, size_t> {
 333   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp* __v) const _NOEXCEPT {
 334     union {
 335       _Tp* __t;
 336       size_t __a;
 337     } __u;
 338     __u.__t = __v;
 339     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 340   }
 341 };
 342
 343 template <>
 344 struct _LIBCPP_TEMPLATE_VIS hash<bool> : public __unary_function<bool, size_t> {
 345   _LIBCPP_HIDE_FROM_ABI size_t operator()(bool __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 346 };
 347
 348 template <>
 349 struct _LIBCPP_TEMPLATE_VIS hash<char> : public __unary_function<char, size_t> {
 350   _LIBCPP_HIDE_FROM_ABI size_t operator()(char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 351 };
 352
 353 template <>
 354 struct _LIBCPP_TEMPLATE_VIS hash<signed char> : public __unary_function<signed char, size_t> {
 355   _LIBCPP_HIDE_FROM_ABI size_t operator()(signed char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 356 };
 357
 358 template <>
 359 struct _LIBCPP_TEMPLATE_VIS hash<unsigned char> : public __unary_function<unsigned char, size_t> {
 360   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 361 };
 362
 363 #ifndef _LIBCPP_HAS_NO_CHAR8_T
 364 template <>
 365 struct _LIBCPP_TEMPLATE_VIS hash<char8_t> : public __unary_function<char8_t, size_t> {
 366   _LIBCPP_HIDE_FROM_ABI size_t operator()(char8_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 367 };
 368 #endif // !_LIBCPP_HAS_NO_CHAR8_T
 369
 370 template <>
 371 struct _LIBCPP_TEMPLATE_VIS hash<char16_t> : public __unary_function<char16_t, size_t> {
 372   _LIBCPP_HIDE_FROM_ABI size_t operator()(char16_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 373 };
 374
 375 template <>
 376 struct _LIBCPP_TEMPLATE_VIS hash<char32_t> : public __unary_function<char32_t, size_t> {
 377   _LIBCPP_HIDE_FROM_ABI size_t operator()(char32_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 378 };
 379
 380 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 381 template <>
 382 struct _LIBCPP_TEMPLATE_VIS hash<wchar_t> : public __unary_function<wchar_t, size_t> {
 383   _LIBCPP_HIDE_FROM_ABI size_t operator()(wchar_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 384 };
 385 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 386
 387 template <>
 388 struct _LIBCPP_TEMPLATE_VIS hash<short> : public __unary_function<short, size_t> {
 389   _LIBCPP_HIDE_FROM_ABI size_t operator()(short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 390 };
 391
 392 template <>
 393 struct _LIBCPP_TEMPLATE_VIS hash<unsigned short> : public __unary_function<unsigned short, size_t> {
 394   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 395 };
 396
 397 template <>
 398 struct _LIBCPP_TEMPLATE_VIS hash<int> : public __unary_function<int, size_t> {
 399   _LIBCPP_HIDE_FROM_ABI size_t operator()(int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 400 };
 401
 402 template <>
 403 struct _LIBCPP_TEMPLATE_VIS hash<unsigned int> : public __unary_function<unsigned int, size_t> {
 404   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 405 };
 406
 407 template <>
 408 struct _LIBCPP_TEMPLATE_VIS hash<long> : public __unary_function<long, size_t> {
 409   _LIBCPP_HIDE_FROM_ABI size_t operator()(long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 410 };
 411
 412 template <>
 413 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long> : public __unary_function<unsigned long, size_t> {
 414   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 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 #ifndef _LIBCPP_HAS_NO_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