libcxx/include/__cxx03/__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___CXX03___FUNCTIONAL_HASH_H
  10 #define _LIBCPP___CXX03___FUNCTIONAL_HASH_H
  11
  12 #include <__cxx03/__config>
  13 #include <__cxx03/__functional/unary_function.h>
  14 #include <__cxx03/__fwd/functional.h>
  15 #include <__cxx03/__type_traits/conjunction.h>
  16 #include <__cxx03/__type_traits/invoke.h>
  17 #include <__cxx03/__type_traits/is_constructible.h>
  18 #include <__cxx03/__type_traits/is_enum.h>
  19 #include <__cxx03/__type_traits/underlying_type.h>
  20 #include <__cxx03/__utility/pair.h>
  21 #include <__cxx03/__utility/swap.h>
  22 #include <__cxx03/cstddef>
  23 #include <__cxx03/cstdint>
  24 #include <__cxx03/cstring>
  25
  26 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  27 #  pragma GCC system_header
  28 #endif
  29
  30 _LIBCPP_BEGIN_NAMESPACE_STD
  31
  32 template <class _Size>
  33 inline _LIBCPP_HIDE_FROM_ABI _Size __loadword(const void* __p) {
  34   _Size __r;
  35   std::memcpy(&__r, __p, sizeof(__r));
  36   return __r;
  37 }
  38
  39 // We use murmur2 when size_t is 32 bits, and cityhash64 when size_t
  40 // is 64 bits.  This is because cityhash64 uses 64bit x 64bit
  41 // multiplication, which can be very slow on 32-bit systems.
  42 template <class _Size, size_t = sizeof(_Size) * __CHAR_BIT__>
  43 struct __murmur2_or_cityhash;
  44
  45 template <class _Size>
  46 struct __murmur2_or_cityhash<_Size, 32> {
  47   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  48   operator()(const void* __key, _Size __len) const {
  49     // murmur2
  50     const _Size __m             = 0x5bd1e995;
  51     const _Size __r             = 24;
  52     _Size __h                   = __len;
  53     const unsigned char* __data = static_cast<const unsigned char*>(__key);
  54     for (; __len >= 4; __data += 4, __len -= 4) {
  55       _Size __k = std::__loadword<_Size>(__data);
  56       __k *= __m;
  57       __k ^= __k >> __r;
  58       __k *= __m;
  59       __h *= __m;
  60       __h ^= __k;
  61     }
  62     switch (__len) {
  63     case 3:
  64       __h ^= static_cast<_Size>(__data[2] << 16);
  65       _LIBCPP_FALLTHROUGH();
  66     case 2:
  67       __h ^= static_cast<_Size>(__data[1] << 8);
  68       _LIBCPP_FALLTHROUGH();
  69     case 1:
  70       __h ^= __data[0];
  71       __h *= __m;
  72     }
  73     __h ^= __h >> 13;
  74     __h *= __m;
  75     __h ^= __h >> 15;
  76     return __h;
  77   }
  78 };
  79
  80 template <class _Size>
  81 struct __murmur2_or_cityhash<_Size, 64> {
  82   // cityhash64
  83   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
  84   operator()(const void* __key, _Size __len) const {
  85     const char* __s = static_cast<const char*>(__key);
  86     if (__len <= 32) {
  87       if (__len <= 16) {
  88         return __hash_len_0_to_16(__s, __len);
  89       } else {
  90         return __hash_len_17_to_32(__s, __len);
  91       }
  92     } else if (__len <= 64) {
  93       return __hash_len_33_to_64(__s, __len);
  94     }
  95
  96     // For strings over 64 bytes we hash the end first, and then as we
  97     // loop we keep 56 bytes of state: v, w, x, y, and z.
  98     _Size __x = std::__loadword<_Size>(__s + __len - 40);
  99     _Size __y = std::__loadword<_Size>(__s + __len - 16) + std::__loadword<_Size>(__s + __len - 56);
 100     _Size __z =
 101         __hash_len_16(std::__loadword<_Size>(__s + __len - 48) + __len, std::__loadword<_Size>(__s + __len - 24));
 102     pair<_Size, _Size> __v = __weak_hash_len_32_with_seeds(__s + __len - 64, __len, __z);
 103     pair<_Size, _Size> __w = __weak_hash_len_32_with_seeds(__s + __len - 32, __y + __k1, __x);
 104     __x                    = __x * __k1 + std::__loadword<_Size>(__s);
 105
 106     // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
 107     __len = (__len - 1) & ~static_cast<_Size>(63);
 108     do {
 109       __x = __rotate(__x + __y + __v.first + std::__loadword<_Size>(__s + 8), 37) * __k1;
 110       __y = __rotate(__y + __v.second + std::__loadword<_Size>(__s + 48), 42) * __k1;
 111       __x ^= __w.second;
 112       __y += __v.first + std::__loadword<_Size>(__s + 40);
 113       __z = __rotate(__z + __w.first, 33) * __k1;
 114       __v = __weak_hash_len_32_with_seeds(__s, __v.second * __k1, __x + __w.first);
 115       __w = __weak_hash_len_32_with_seeds(__s + 32, __z + __w.second, __y + std::__loadword<_Size>(__s + 16));
 116       std::swap(__z, __x);
 117       __s += 64;
 118       __len -= 64;
 119     } while (__len != 0);
 120     return __hash_len_16(__hash_len_16(__v.first, __w.first) + __shift_mix(__y) * __k1 + __z,
 121                          __hash_len_16(__v.second, __w.second) + __x);
 122   }
 123
 124 private:
 125   // Some primes between 2^63 and 2^64.
 126   static const _Size __k0 = 0xc3a5c85c97cb3127ULL;
 127   static const _Size __k1 = 0xb492b66fbe98f273ULL;
 128   static const _Size __k2 = 0x9ae16a3b2f90404fULL;
 129   static const _Size __k3 = 0xc949d7c7509e6557ULL;
 130
 131   _LIBCPP_HIDE_FROM_ABI static _Size __rotate(_Size __val, int __shift) {
 132     return __shift == 0 ? __val : ((__val >> __shift) | (__val << (64 - __shift)));
 133   }
 134
 135   _LIBCPP_HIDE_FROM_ABI static _Size __rotate_by_at_least_1(_Size __val, int __shift) {
 136     return (__val >> __shift) | (__val << (64 - __shift));
 137   }
 138
 139   _LIBCPP_HIDE_FROM_ABI static _Size __shift_mix(_Size __val) { return __val ^ (__val >> 47); }
 140
 141   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size __hash_len_16(_Size __u, _Size __v) {
 142     const _Size __mul = 0x9ddfea08eb382d69ULL;
 143     _Size __a         = (__u ^ __v) * __mul;
 144     __a ^= (__a >> 47);
 145     _Size __b = (__v ^ __a) * __mul;
 146     __b ^= (__b >> 47);
 147     __b *= __mul;
 148     return __b;
 149   }
 150
 151   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 152   __hash_len_0_to_16(const char* __s, _Size __len) {
 153     if (__len > 8) {
 154       const _Size __a = std::__loadword<_Size>(__s);
 155       const _Size __b = std::__loadword<_Size>(__s + __len - 8);
 156       return __hash_len_16(__a, __rotate_by_at_least_1(__b + __len, __len)) ^ __b;
 157     }
 158     if (__len >= 4) {
 159       const uint32_t __a = std::__loadword<uint32_t>(__s);
 160       const uint32_t __b = std::__loadword<uint32_t>(__s + __len - 4);
 161 #ifdef _LIBCPP_ABI_FIX_CITYHASH_IMPLEMENTATION
 162       return __hash_len_16(__len + (static_cast<_Size>(__a) << 3), __b);
 163 #else
 164       return __hash_len_16(__len + (__a << 3), __b);
 165 #endif
 166     }
 167     if (__len > 0) {
 168       const unsigned char __a = static_cast<unsigned char>(__s[0]);
 169       const unsigned char __b = static_cast<unsigned char>(__s[__len >> 1]);
 170       const unsigned char __c = static_cast<unsigned char>(__s[__len - 1]);
 171       const uint32_t __y      = static_cast<uint32_t>(__a) + (static_cast<uint32_t>(__b) << 8);
 172       const uint32_t __z      = __len + (static_cast<uint32_t>(__c) << 2);
 173       return __shift_mix(__y * __k2 ^ __z * __k3) * __k2;
 174     }
 175     return __k2;
 176   }
 177
 178   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 179   __hash_len_17_to_32(const char* __s, _Size __len) {
 180     const _Size __a = std::__loadword<_Size>(__s) * __k1;
 181     const _Size __b = std::__loadword<_Size>(__s + 8);
 182     const _Size __c = std::__loadword<_Size>(__s + __len - 8) * __k2;
 183     const _Size __d = std::__loadword<_Size>(__s + __len - 16) * __k0;
 184     return __hash_len_16(
 185         __rotate(__a - __b, 43) + __rotate(__c, 30) + __d, __a + __rotate(__b ^ __k3, 20) - __c + __len);
 186   }
 187
 188   // Return a 16-byte hash for 48 bytes.  Quick and dirty.
 189   // Callers do best to use "random-looking" values for a and b.
 190   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 191   __weak_hash_len_32_with_seeds(_Size __w, _Size __x, _Size __y, _Size __z, _Size __a, _Size __b) {
 192     __a += __w;
 193     __b             = __rotate(__b + __a + __z, 21);
 194     const _Size __c = __a;
 195     __a += __x;
 196     __a += __y;
 197     __b += __rotate(__a, 44);
 198     return pair<_Size, _Size>(__a + __z, __b + __c);
 199   }
 200
 201   // Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
 202   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
 203   __weak_hash_len_32_with_seeds(const char* __s, _Size __a, _Size __b) {
 204     return __weak_hash_len_32_with_seeds(
 205         std::__loadword<_Size>(__s),
 206         std::__loadword<_Size>(__s + 8),
 207         std::__loadword<_Size>(__s + 16),
 208         std::__loadword<_Size>(__s + 24),
 209         __a,
 210         __b);
 211   }
 212
 213   // Return an 8-byte hash for 33 to 64 bytes.
 214   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
 215   __hash_len_33_to_64(const char* __s, size_t __len) {
 216     _Size __z = std::__loadword<_Size>(__s + 24);
 217     _Size __a = std::__loadword<_Size>(__s) + (__len + std::__loadword<_Size>(__s + __len - 16)) * __k0;
 218     _Size __b = __rotate(__a + __z, 52);
 219     _Size __c = __rotate(__a, 37);
 220     __a += std::__loadword<_Size>(__s + 8);
 221     __c += __rotate(__a, 7);
 222     __a += std::__loadword<_Size>(__s + 16);
 223     _Size __vf = __a + __z;
 224     _Size __vs = __b + __rotate(__a, 31) + __c;
 225     __a        = std::__loadword<_Size>(__s + 16) + std::__loadword<_Size>(__s + __len - 32);
 226     __z += std::__loadword<_Size>(__s + __len - 8);
 227     __b = __rotate(__a + __z, 52);
 228     __c = __rotate(__a, 37);
 229     __a += std::__loadword<_Size>(__s + __len - 24);
 230     __c += __rotate(__a, 7);
 231     __a += std::__loadword<_Size>(__s + __len - 16);
 232     _Size __wf = __a + __z;
 233     _Size __ws = __b + __rotate(__a, 31) + __c;
 234     _Size __r  = __shift_mix((__vf + __ws) * __k2 + (__wf + __vs) * __k0);
 235     return __shift_mix(__r * __k0 + __vs) * __k2;
 236   }
 237 };
 238
 239 template <class _Tp, size_t = sizeof(_Tp) / sizeof(size_t)>
 240 struct __scalar_hash;
 241
 242 template <class _Tp>
 243 struct __scalar_hash<_Tp, 0> : public __unary_function<_Tp, size_t> {
 244   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 245     union {
 246       _Tp __t;
 247       size_t __a;
 248     } __u;
 249     __u.__a = 0;
 250     __u.__t = __v;
 251     return __u.__a;
 252   }
 253 };
 254
 255 template <class _Tp>
 256 struct __scalar_hash<_Tp, 1> : public __unary_function<_Tp, size_t> {
 257   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 258     union {
 259       _Tp __t;
 260       size_t __a;
 261     } __u;
 262     __u.__t = __v;
 263     return __u.__a;
 264   }
 265 };
 266
 267 template <class _Tp>
 268 struct __scalar_hash<_Tp, 2> : public __unary_function<_Tp, size_t> {
 269   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 270     union {
 271       _Tp __t;
 272       struct {
 273         size_t __a;
 274         size_t __b;
 275       } __s;
 276     } __u;
 277     __u.__t = __v;
 278     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 279   }
 280 };
 281
 282 template <class _Tp>
 283 struct __scalar_hash<_Tp, 3> : public __unary_function<_Tp, size_t> {
 284   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 285     union {
 286       _Tp __t;
 287       struct {
 288         size_t __a;
 289         size_t __b;
 290         size_t __c;
 291       } __s;
 292     } __u;
 293     __u.__t = __v;
 294     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 295   }
 296 };
 297
 298 template <class _Tp>
 299 struct __scalar_hash<_Tp, 4> : public __unary_function<_Tp, size_t> {
 300   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 301     union {
 302       _Tp __t;
 303       struct {
 304         size_t __a;
 305         size_t __b;
 306         size_t __c;
 307         size_t __d;
 308       } __s;
 309     } __u;
 310     __u.__t = __v;
 311     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 312   }
 313 };
 314
 315 struct _PairT {
 316   size_t first;
 317   size_t second;
 318 };
 319
 320 _LIBCPP_HIDE_FROM_ABI inline size_t __hash_combine(size_t __lhs, size_t __rhs) _NOEXCEPT {
 321   typedef __scalar_hash<_PairT> _HashT;
 322   const _PairT __p = {__lhs, __rhs};
 323   return _HashT()(__p);
 324 }
 325
 326 template <class _Tp>
 327 struct _LIBCPP_TEMPLATE_VIS hash<_Tp*> : public __unary_function<_Tp*, size_t> {
 328   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp* __v) const _NOEXCEPT {
 329     union {
 330       _Tp* __t;
 331       size_t __a;
 332     } __u;
 333     __u.__t = __v;
 334     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
 335   }
 336 };
 337
 338 template <>
 339 struct _LIBCPP_TEMPLATE_VIS hash<bool> : public __unary_function<bool, size_t> {
 340   _LIBCPP_HIDE_FROM_ABI size_t operator()(bool __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 341 };
 342
 343 template <>
 344 struct _LIBCPP_TEMPLATE_VIS hash<char> : public __unary_function<char, size_t> {
 345   _LIBCPP_HIDE_FROM_ABI size_t operator()(char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 346 };
 347
 348 template <>
 349 struct _LIBCPP_TEMPLATE_VIS hash<signed char> : public __unary_function<signed char, size_t> {
 350   _LIBCPP_HIDE_FROM_ABI size_t operator()(signed char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 351 };
 352
 353 template <>
 354 struct _LIBCPP_TEMPLATE_VIS hash<unsigned char> : public __unary_function<unsigned char, size_t> {
 355   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 356 };
 357
 358 #ifndef _LIBCPP_HAS_NO_CHAR8_T
 359 template <>
 360 struct _LIBCPP_TEMPLATE_VIS hash<char8_t> : public __unary_function<char8_t, size_t> {
 361   _LIBCPP_HIDE_FROM_ABI size_t operator()(char8_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 362 };
 363 #endif // !_LIBCPP_HAS_NO_CHAR8_T
 364
 365 template <>
 366 struct _LIBCPP_TEMPLATE_VIS hash<char16_t> : public __unary_function<char16_t, size_t> {
 367   _LIBCPP_HIDE_FROM_ABI size_t operator()(char16_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 368 };
 369
 370 template <>
 371 struct _LIBCPP_TEMPLATE_VIS hash<char32_t> : public __unary_function<char32_t, size_t> {
 372   _LIBCPP_HIDE_FROM_ABI size_t operator()(char32_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 373 };
 374
 375 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
 376 template <>
 377 struct _LIBCPP_TEMPLATE_VIS hash<wchar_t> : public __unary_function<wchar_t, size_t> {
 378   _LIBCPP_HIDE_FROM_ABI size_t operator()(wchar_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 379 };
 380 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
 381
 382 template <>
 383 struct _LIBCPP_TEMPLATE_VIS hash<short> : public __unary_function<short, size_t> {
 384   _LIBCPP_HIDE_FROM_ABI size_t operator()(short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 385 };
 386
 387 template <>
 388 struct _LIBCPP_TEMPLATE_VIS hash<unsigned short> : public __unary_function<unsigned short, size_t> {
 389   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 390 };
 391
 392 template <>
 393 struct _LIBCPP_TEMPLATE_VIS hash<int> : public __unary_function<int, size_t> {
 394   _LIBCPP_HIDE_FROM_ABI size_t operator()(int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 395 };
 396
 397 template <>
 398 struct _LIBCPP_TEMPLATE_VIS hash<unsigned int> : public __unary_function<unsigned int, size_t> {
 399   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 400 };
 401
 402 template <>
 403 struct _LIBCPP_TEMPLATE_VIS hash<long> : public __unary_function<long, size_t> {
 404   _LIBCPP_HIDE_FROM_ABI size_t operator()(long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 405 };
 406
 407 template <>
 408 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long> : public __unary_function<unsigned long, size_t> {
 409   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
 410 };
 411
 412 template <>
 413 struct _LIBCPP_TEMPLATE_VIS hash<long long> : public __scalar_hash<long long> {};
 414
 415 template <>
 416 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long long> : public __scalar_hash<unsigned long long> {};
 417
 418 #ifndef _LIBCPP_HAS_NO_INT128
 419
 420 template <>
 421 struct _LIBCPP_TEMPLATE_VIS hash<__int128_t> : public __scalar_hash<__int128_t> {};
 422
 423 template <>
 424 struct _LIBCPP_TEMPLATE_VIS hash<__uint128_t> : public __scalar_hash<__uint128_t> {};
 425
 426 #endif
 427
 428 template <>
 429 struct _LIBCPP_TEMPLATE_VIS hash<float> : public __scalar_hash<float> {
 430   _LIBCPP_HIDE_FROM_ABI size_t operator()(float __v) const _NOEXCEPT {
 431     // -0.0 and 0.0 should return same hash
 432     if (__v == 0.0f)
 433       return 0;
 434     return __scalar_hash<float>::operator()(__v);
 435   }
 436 };
 437
 438 template <>
 439 struct _LIBCPP_TEMPLATE_VIS hash<double> : public __scalar_hash<double> {
 440   _LIBCPP_HIDE_FROM_ABI size_t operator()(double __v) const _NOEXCEPT {
 441     // -0.0 and 0.0 should return same hash
 442     if (__v == 0.0)
 443       return 0;
 444     return __scalar_hash<double>::operator()(__v);
 445   }
 446 };
 447
 448 template <>
 449 struct _LIBCPP_TEMPLATE_VIS hash<long double> : public __scalar_hash<long double> {
 450   _LIBCPP_HIDE_FROM_ABI size_t operator()(long double __v) const _NOEXCEPT {
 451     // -0.0 and 0.0 should return same hash
 452     if (__v == 0.0L)
 453       return 0;
 454 #if defined(__i386__) || (defined(__x86_64__) && defined(__ILP32__))
 455     // Zero out padding bits
 456     union {
 457       long double __t;
 458       struct {
 459         size_t __a;
 460         size_t __b;
 461         size_t __c;
 462         size_t __d;
 463       } __s;
 464     } __u;
 465     __u.__s.__a = 0;
 466     __u.__s.__b = 0;
 467     __u.__s.__c = 0;
 468     __u.__s.__d = 0;
 469     __u.__t     = __v;
 470     return __u.__s.__a ^ __u.__s.__b ^ __u.__s.__c ^ __u.__s.__d;
 471 #elif defined(__x86_64__)
 472     // Zero out padding bits
 473     union {
 474       long double __t;
 475       struct {
 476         size_t __a;
 477         size_t __b;
 478       } __s;
 479     } __u;
 480     __u.__s.__a = 0;
 481     __u.__s.__b = 0;
 482     __u.__t     = __v;
 483     return __u.__s.__a ^ __u.__s.__b;
 484 #else
 485     return __scalar_hash<long double>::operator()(__v);
 486 #endif
 487   }
 488 };
 489
 490 template <class _Tp, bool = is_enum<_Tp>::value>
 491 struct _LIBCPP_TEMPLATE_VIS __enum_hash : public __unary_function<_Tp, size_t> {
 492   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
 493     typedef typename underlying_type<_Tp>::type type;
 494     return hash<type>()(static_cast<type>(__v));
 495   }
 496 };
 497 template <class _Tp>
 498 struct _LIBCPP_TEMPLATE_VIS __enum_hash<_Tp, false> {
 499   __enum_hash()                              = delete;
 500   __enum_hash(__enum_hash const&)            = delete;
 501   __enum_hash& operator=(__enum_hash const&) = delete;
 502 };
 503
 504 template <class _Tp>
 505 struct _LIBCPP_TEMPLATE_VIS hash : public __enum_hash<_Tp> {};
 506
 507 #if _LIBCPP_STD_VER >= 17
 508
 509 template <>
 510 struct _LIBCPP_TEMPLATE_VIS hash<nullptr_t> : public __unary_function<nullptr_t, size_t> {
 511   _LIBCPP_HIDE_FROM_ABI size_t operator()(nullptr_t) const _NOEXCEPT { return 662607004ull; }
 512 };
 513 #endif
 514
 515 #ifndef _LIBCPP_CXX03_LANG
 516 template <class _Key, class _Hash>
 517 using __check_hash_requirements _LIBCPP_NODEBUG =
 518     integral_constant<bool,
 519                       is_copy_constructible<_Hash>::value && is_move_constructible<_Hash>::value &&
 520                           __invokable_r<size_t, _Hash, _Key const&>::value >;
 521
 522 template <class _Key, class _Hash = hash<_Key> >
 523 using __has_enabled_hash _LIBCPP_NODEBUG =
 524     integral_constant<bool, __check_hash_requirements<_Key, _Hash>::value && is_default_constructible<_Hash>::value >;
 525
 526 #  if _LIBCPP_STD_VER >= 17
 527 template <class _Type, class>
 528 using __enable_hash_helper_imp _LIBCPP_NODEBUG = _Type;
 529
 530 template <class _Type, class... _Keys>
 531 using __enable_hash_helper _LIBCPP_NODEBUG =
 532     __enable_hash_helper_imp<_Type, __enable_if_t<__all<__has_enabled_hash<_Keys>::value...>::value> >;
 533 #  else
 534 template <class _Type, class...>
 535 using __enable_hash_helper _LIBCPP_NODEBUG = _Type;
 536 #  endif
 537
 538 #endif // !_LIBCPP_CXX03_LANG
 539
 540 _LIBCPP_END_NAMESPACE_STD
 541
 542 #endif // _LIBCPP___CXX03___FUNCTIONAL_HASH_H