__cxx03/__functional/hash.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___CXX03___FUNCTIONAL_HASH_H
0010 #define _LIBCPP___CXX03___FUNCTIONAL_HASH_H
0011
0012 #include <__cxx03/__config>
0013 #include <__cxx03/__functional/unary_function.h>
0014 #include <__cxx03/__fwd/functional.h>
0015 #include <__cxx03/__type_traits/conjunction.h>
0016 #include <__cxx03/__type_traits/invoke.h>
0017 #include <__cxx03/__type_traits/is_constructible.h>
0018 #include <__cxx03/__type_traits/is_enum.h>
0019 #include <__cxx03/__type_traits/underlying_type.h>
0020 #include <__cxx03/__utility/pair.h>
0021 #include <__cxx03/__utility/swap.h>
0022 #include <__cxx03/cstddef>
0023 #include <__cxx03/cstdint>
0024 #include <__cxx03/cstring>
0025
0026 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0027 #  pragma GCC system_header
0028 #endif
0029
0030 _LIBCPP_BEGIN_NAMESPACE_STD
0031
0032 template <class _Size>
0033 inline _LIBCPP_HIDE_FROM_ABI _Size __loadword(const void* __p) {
0034   _Size __r;
0035   std::memcpy(&__r, __p, sizeof(__r));
0036   return __r;
0037 }
0038
0039 // We use murmur2 when size_t is 32 bits, and cityhash64 when size_t
0040 // is 64 bits.  This is because cityhash64 uses 64bit x 64bit
0041 // multiplication, which can be very slow on 32-bit systems.
0042 template <class _Size, size_t = sizeof(_Size) * __CHAR_BIT__>
0043 struct __murmur2_or_cityhash;
0044
0045 template <class _Size>
0046 struct __murmur2_or_cityhash<_Size, 32> {
0047   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
0048   operator()(const void* __key, _Size __len) const {
0049     // murmur2
0050     const _Size __m             = 0x5bd1e995;
0051     const _Size __r             = 24;
0052     _Size __h                   = __len;
0053     const unsigned char* __data = static_cast<const unsigned char*>(__key);
0054     for (; __len >= 4; __data += 4, __len -= 4) {
0055       _Size __k = std::__loadword<_Size>(__data);
0056       __k *= __m;
0057       __k ^= __k >> __r;
0058       __k *= __m;
0059       __h *= __m;
0060       __h ^= __k;
0061     }
0062     switch (__len) {
0063     case 3:
0064       __h ^= static_cast<_Size>(__data[2] << 16);
0065       _LIBCPP_FALLTHROUGH();
0066     case 2:
0067       __h ^= static_cast<_Size>(__data[1] << 8);
0068       _LIBCPP_FALLTHROUGH();
0069     case 1:
0070       __h ^= __data[0];
0071       __h *= __m;
0072     }
0073     __h ^= __h >> 13;
0074     __h *= __m;
0075     __h ^= __h >> 15;
0076     return __h;
0077   }
0078 };
0079
0080 template <class _Size>
0081 struct __murmur2_or_cityhash<_Size, 64> {
0082   // cityhash64
0083   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK _Size
0084   operator()(const void* __key, _Size __len) const {
0085     const char* __s = static_cast<const char*>(__key);
0086     if (__len <= 32) {
0087       if (__len <= 16) {
0088         return __hash_len_0_to_16(__s, __len);
0089       } else {
0090         return __hash_len_17_to_32(__s, __len);
0091       }
0092     } else if (__len <= 64) {
0093       return __hash_len_33_to_64(__s, __len);
0094     }
0095
0096     // For strings over 64 bytes we hash the end first, and then as we
0097     // loop we keep 56 bytes of state: v, w, x, y, and z.
0098     _Size __x = std::__loadword<_Size>(__s + __len - 40);
0099     _Size __y = std::__loadword<_Size>(__s + __len - 16) + std::__loadword<_Size>(__s + __len - 56);
0100     _Size __z =
0101         __hash_len_16(std::__loadword<_Size>(__s + __len - 48) + __len, std::__loadword<_Size>(__s + __len - 24));
0102     pair<_Size, _Size> __v = __weak_hash_len_32_with_seeds(__s + __len - 64, __len, __z);
0103     pair<_Size, _Size> __w = __weak_hash_len_32_with_seeds(__s + __len - 32, __y + __k1, __x);
0104     __x                    = __x * __k1 + std::__loadword<_Size>(__s);
0105
0106     // Decrease len to the nearest multiple of 64, and operate on 64-byte chunks.
0107     __len = (__len - 1) & ~static_cast<_Size>(63);
0108     do {
0109       __x = __rotate(__x + __y + __v.first + std::__loadword<_Size>(__s + 8), 37) * __k1;
0110       __y = __rotate(__y + __v.second + std::__loadword<_Size>(__s + 48), 42) * __k1;
0111       __x ^= __w.second;
0112       __y += __v.first + std::__loadword<_Size>(__s + 40);
0113       __z = __rotate(__z + __w.first, 33) * __k1;
0114       __v = __weak_hash_len_32_with_seeds(__s, __v.second * __k1, __x + __w.first);
0115       __w = __weak_hash_len_32_with_seeds(__s + 32, __z + __w.second, __y + std::__loadword<_Size>(__s + 16));
0116       std::swap(__z, __x);
0117       __s += 64;
0118       __len -= 64;
0119     } while (__len != 0);
0120     return __hash_len_16(__hash_len_16(__v.first, __w.first) + __shift_mix(__y) * __k1 + __z,
0121                          __hash_len_16(__v.second, __w.second) + __x);
0122   }
0123
0124 private:
0125   // Some primes between 2^63 and 2^64.
0126   static const _Size __k0 = 0xc3a5c85c97cb3127ULL;
0127   static const _Size __k1 = 0xb492b66fbe98f273ULL;
0128   static const _Size __k2 = 0x9ae16a3b2f90404fULL;
0129   static const _Size __k3 = 0xc949d7c7509e6557ULL;
0130
0131   _LIBCPP_HIDE_FROM_ABI static _Size __rotate(_Size __val, int __shift) {
0132     return __shift == 0 ? __val : ((__val >> __shift) | (__val << (64 - __shift)));
0133   }
0134
0135   _LIBCPP_HIDE_FROM_ABI static _Size __rotate_by_at_least_1(_Size __val, int __shift) {
0136     return (__val >> __shift) | (__val << (64 - __shift));
0137   }
0138
0139   _LIBCPP_HIDE_FROM_ABI static _Size __shift_mix(_Size __val) { return __val ^ (__val >> 47); }
0140
0141   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size __hash_len_16(_Size __u, _Size __v) {
0142     const _Size __mul = 0x9ddfea08eb382d69ULL;
0143     _Size __a         = (__u ^ __v) * __mul;
0144     __a ^= (__a >> 47);
0145     _Size __b = (__v ^ __a) * __mul;
0146     __b ^= (__b >> 47);
0147     __b *= __mul;
0148     return __b;
0149   }
0150
0151   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
0152   __hash_len_0_to_16(const char* __s, _Size __len) {
0153     if (__len > 8) {
0154       const _Size __a = std::__loadword<_Size>(__s);
0155       const _Size __b = std::__loadword<_Size>(__s + __len - 8);
0156       return __hash_len_16(__a, __rotate_by_at_least_1(__b + __len, __len)) ^ __b;
0157     }
0158     if (__len >= 4) {
0159       const uint32_t __a = std::__loadword<uint32_t>(__s);
0160       const uint32_t __b = std::__loadword<uint32_t>(__s + __len - 4);
0161 #ifdef _LIBCPP_ABI_FIX_CITYHASH_IMPLEMENTATION
0162       return __hash_len_16(__len + (static_cast<_Size>(__a) << 3), __b);
0163 #else
0164       return __hash_len_16(__len + (__a << 3), __b);
0165 #endif
0166     }
0167     if (__len > 0) {
0168       const unsigned char __a = static_cast<unsigned char>(__s[0]);
0169       const unsigned char __b = static_cast<unsigned char>(__s[__len >> 1]);
0170       const unsigned char __c = static_cast<unsigned char>(__s[__len - 1]);
0171       const uint32_t __y      = static_cast<uint32_t>(__a) + (static_cast<uint32_t>(__b) << 8);
0172       const uint32_t __z      = __len + (static_cast<uint32_t>(__c) << 2);
0173       return __shift_mix(__y * __k2 ^ __z * __k3) * __k2;
0174     }
0175     return __k2;
0176   }
0177
0178   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
0179   __hash_len_17_to_32(const char* __s, _Size __len) {
0180     const _Size __a = std::__loadword<_Size>(__s) * __k1;
0181     const _Size __b = std::__loadword<_Size>(__s + 8);
0182     const _Size __c = std::__loadword<_Size>(__s + __len - 8) * __k2;
0183     const _Size __d = std::__loadword<_Size>(__s + __len - 16) * __k0;
0184     return __hash_len_16(
0185         __rotate(__a - __b, 43) + __rotate(__c, 30) + __d, __a + __rotate(__b ^ __k3, 20) - __c + __len);
0186   }
0187
0188   // Return a 16-byte hash for 48 bytes.  Quick and dirty.
0189   // Callers do best to use "random-looking" values for a and b.
0190   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
0191   __weak_hash_len_32_with_seeds(_Size __w, _Size __x, _Size __y, _Size __z, _Size __a, _Size __b) {
0192     __a += __w;
0193     __b             = __rotate(__b + __a + __z, 21);
0194     const _Size __c = __a;
0195     __a += __x;
0196     __a += __y;
0197     __b += __rotate(__a, 44);
0198     return pair<_Size, _Size>(__a + __z, __b + __c);
0199   }
0200
0201   // Return a 16-byte hash for s[0] ... s[31], a, and b.  Quick and dirty.
0202   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static pair<_Size, _Size>
0203   __weak_hash_len_32_with_seeds(const char* __s, _Size __a, _Size __b) {
0204     return __weak_hash_len_32_with_seeds(
0205         std::__loadword<_Size>(__s),
0206         std::__loadword<_Size>(__s + 8),
0207         std::__loadword<_Size>(__s + 16),
0208         std::__loadword<_Size>(__s + 24),
0209         __a,
0210         __b);
0211   }
0212
0213   // Return an 8-byte hash for 33 to 64 bytes.
0214   _LIBCPP_HIDE_FROM_ABI _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK static _Size
0215   __hash_len_33_to_64(const char* __s, size_t __len) {
0216     _Size __z = std::__loadword<_Size>(__s + 24);
0217     _Size __a = std::__loadword<_Size>(__s) + (__len + std::__loadword<_Size>(__s + __len - 16)) * __k0;
0218     _Size __b = __rotate(__a + __z, 52);
0219     _Size __c = __rotate(__a, 37);
0220     __a += std::__loadword<_Size>(__s + 8);
0221     __c += __rotate(__a, 7);
0222     __a += std::__loadword<_Size>(__s + 16);
0223     _Size __vf = __a + __z;
0224     _Size __vs = __b + __rotate(__a, 31) + __c;
0225     __a        = std::__loadword<_Size>(__s + 16) + std::__loadword<_Size>(__s + __len - 32);
0226     __z += std::__loadword<_Size>(__s + __len - 8);
0227     __b = __rotate(__a + __z, 52);
0228     __c = __rotate(__a, 37);
0229     __a += std::__loadword<_Size>(__s + __len - 24);
0230     __c += __rotate(__a, 7);
0231     __a += std::__loadword<_Size>(__s + __len - 16);
0232     _Size __wf = __a + __z;
0233     _Size __ws = __b + __rotate(__a, 31) + __c;
0234     _Size __r  = __shift_mix((__vf + __ws) * __k2 + (__wf + __vs) * __k0);
0235     return __shift_mix(__r * __k0 + __vs) * __k2;
0236   }
0237 };
0238
0239 template <class _Tp, size_t = sizeof(_Tp) / sizeof(size_t)>
0240 struct __scalar_hash;
0241
0242 template <class _Tp>
0243 struct __scalar_hash<_Tp, 0> : public __unary_function<_Tp, size_t> {
0244   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0245     union {
0246       _Tp __t;
0247       size_t __a;
0248     } __u;
0249     __u.__a = 0;
0250     __u.__t = __v;
0251     return __u.__a;
0252   }
0253 };
0254
0255 template <class _Tp>
0256 struct __scalar_hash<_Tp, 1> : public __unary_function<_Tp, size_t> {
0257   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0258     union {
0259       _Tp __t;
0260       size_t __a;
0261     } __u;
0262     __u.__t = __v;
0263     return __u.__a;
0264   }
0265 };
0266
0267 template <class _Tp>
0268 struct __scalar_hash<_Tp, 2> : public __unary_function<_Tp, size_t> {
0269   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0270     union {
0271       _Tp __t;
0272       struct {
0273         size_t __a;
0274         size_t __b;
0275       } __s;
0276     } __u;
0277     __u.__t = __v;
0278     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
0279   }
0280 };
0281
0282 template <class _Tp>
0283 struct __scalar_hash<_Tp, 3> : public __unary_function<_Tp, size_t> {
0284   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0285     union {
0286       _Tp __t;
0287       struct {
0288         size_t __a;
0289         size_t __b;
0290         size_t __c;
0291       } __s;
0292     } __u;
0293     __u.__t = __v;
0294     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
0295   }
0296 };
0297
0298 template <class _Tp>
0299 struct __scalar_hash<_Tp, 4> : public __unary_function<_Tp, size_t> {
0300   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0301     union {
0302       _Tp __t;
0303       struct {
0304         size_t __a;
0305         size_t __b;
0306         size_t __c;
0307         size_t __d;
0308       } __s;
0309     } __u;
0310     __u.__t = __v;
0311     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
0312   }
0313 };
0314
0315 struct _PairT {
0316   size_t first;
0317   size_t second;
0318 };
0319
0320 _LIBCPP_HIDE_FROM_ABI inline size_t __hash_combine(size_t __lhs, size_t __rhs) _NOEXCEPT {
0321   typedef __scalar_hash<_PairT> _HashT;
0322   const _PairT __p = {__lhs, __rhs};
0323   return _HashT()(__p);
0324 }
0325
0326 template <class _Tp>
0327 struct _LIBCPP_TEMPLATE_VIS hash<_Tp*> : public __unary_function<_Tp*, size_t> {
0328   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp* __v) const _NOEXCEPT {
0329     union {
0330       _Tp* __t;
0331       size_t __a;
0332     } __u;
0333     __u.__t = __v;
0334     return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
0335   }
0336 };
0337
0338 template <>
0339 struct _LIBCPP_TEMPLATE_VIS hash<bool> : public __unary_function<bool, size_t> {
0340   _LIBCPP_HIDE_FROM_ABI size_t operator()(bool __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0341 };
0342
0343 template <>
0344 struct _LIBCPP_TEMPLATE_VIS hash<char> : public __unary_function<char, size_t> {
0345   _LIBCPP_HIDE_FROM_ABI size_t operator()(char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0346 };
0347
0348 template <>
0349 struct _LIBCPP_TEMPLATE_VIS hash<signed char> : public __unary_function<signed char, size_t> {
0350   _LIBCPP_HIDE_FROM_ABI size_t operator()(signed char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0351 };
0352
0353 template <>
0354 struct _LIBCPP_TEMPLATE_VIS hash<unsigned char> : public __unary_function<unsigned char, size_t> {
0355   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned char __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0356 };
0357
0358 #ifndef _LIBCPP_HAS_NO_CHAR8_T
0359 template <>
0360 struct _LIBCPP_TEMPLATE_VIS hash<char8_t> : public __unary_function<char8_t, size_t> {
0361   _LIBCPP_HIDE_FROM_ABI size_t operator()(char8_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0362 };
0363 #endif // !_LIBCPP_HAS_NO_CHAR8_T
0364
0365 template <>
0366 struct _LIBCPP_TEMPLATE_VIS hash<char16_t> : public __unary_function<char16_t, size_t> {
0367   _LIBCPP_HIDE_FROM_ABI size_t operator()(char16_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0368 };
0369
0370 template <>
0371 struct _LIBCPP_TEMPLATE_VIS hash<char32_t> : public __unary_function<char32_t, size_t> {
0372   _LIBCPP_HIDE_FROM_ABI size_t operator()(char32_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0373 };
0374
0375 #ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
0376 template <>
0377 struct _LIBCPP_TEMPLATE_VIS hash<wchar_t> : public __unary_function<wchar_t, size_t> {
0378   _LIBCPP_HIDE_FROM_ABI size_t operator()(wchar_t __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0379 };
0380 #endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
0381
0382 template <>
0383 struct _LIBCPP_TEMPLATE_VIS hash<short> : public __unary_function<short, size_t> {
0384   _LIBCPP_HIDE_FROM_ABI size_t operator()(short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0385 };
0386
0387 template <>
0388 struct _LIBCPP_TEMPLATE_VIS hash<unsigned short> : public __unary_function<unsigned short, size_t> {
0389   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned short __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0390 };
0391
0392 template <>
0393 struct _LIBCPP_TEMPLATE_VIS hash<int> : public __unary_function<int, size_t> {
0394   _LIBCPP_HIDE_FROM_ABI size_t operator()(int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0395 };
0396
0397 template <>
0398 struct _LIBCPP_TEMPLATE_VIS hash<unsigned int> : public __unary_function<unsigned int, size_t> {
0399   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned int __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0400 };
0401
0402 template <>
0403 struct _LIBCPP_TEMPLATE_VIS hash<long> : public __unary_function<long, size_t> {
0404   _LIBCPP_HIDE_FROM_ABI size_t operator()(long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0405 };
0406
0407 template <>
0408 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long> : public __unary_function<unsigned long, size_t> {
0409   _LIBCPP_HIDE_FROM_ABI size_t operator()(unsigned long __v) const _NOEXCEPT { return static_cast<size_t>(__v); }
0410 };
0411
0412 template <>
0413 struct _LIBCPP_TEMPLATE_VIS hash<long long> : public __scalar_hash<long long> {};
0414
0415 template <>
0416 struct _LIBCPP_TEMPLATE_VIS hash<unsigned long long> : public __scalar_hash<unsigned long long> {};
0417
0418 #ifndef _LIBCPP_HAS_NO_INT128
0419
0420 template <>
0421 struct _LIBCPP_TEMPLATE_VIS hash<__int128_t> : public __scalar_hash<__int128_t> {};
0422
0423 template <>
0424 struct _LIBCPP_TEMPLATE_VIS hash<__uint128_t> : public __scalar_hash<__uint128_t> {};
0425
0426 #endif
0427
0428 template <>
0429 struct _LIBCPP_TEMPLATE_VIS hash<float> : public __scalar_hash<float> {
0430   _LIBCPP_HIDE_FROM_ABI size_t operator()(float __v) const _NOEXCEPT {
0431     // -0.0 and 0.0 should return same hash
0432     if (__v == 0.0f)
0433       return 0;
0434     return __scalar_hash<float>::operator()(__v);
0435   }
0436 };
0437
0438 template <>
0439 struct _LIBCPP_TEMPLATE_VIS hash<double> : public __scalar_hash<double> {
0440   _LIBCPP_HIDE_FROM_ABI size_t operator()(double __v) const _NOEXCEPT {
0441     // -0.0 and 0.0 should return same hash
0442     if (__v == 0.0)
0443       return 0;
0444     return __scalar_hash<double>::operator()(__v);
0445   }
0446 };
0447
0448 template <>
0449 struct _LIBCPP_TEMPLATE_VIS hash<long double> : public __scalar_hash<long double> {
0450   _LIBCPP_HIDE_FROM_ABI size_t operator()(long double __v) const _NOEXCEPT {
0451     // -0.0 and 0.0 should return same hash
0452     if (__v == 0.0L)
0453       return 0;
0454 #if defined(__i386__) || (defined(__x86_64__) && defined(__ILP32__))
0455     // Zero out padding bits
0456     union {
0457       long double __t;
0458       struct {
0459         size_t __a;
0460         size_t __b;
0461         size_t __c;
0462         size_t __d;
0463       } __s;
0464     } __u;
0465     __u.__s.__a = 0;
0466     __u.__s.__b = 0;
0467     __u.__s.__c = 0;
0468     __u.__s.__d = 0;
0469     __u.__t     = __v;
0470     return __u.__s.__a ^ __u.__s.__b ^ __u.__s.__c ^ __u.__s.__d;
0471 #elif defined(__x86_64__)
0472     // Zero out padding bits
0473     union {
0474       long double __t;
0475       struct {
0476         size_t __a;
0477         size_t __b;
0478       } __s;
0479     } __u;
0480     __u.__s.__a = 0;
0481     __u.__s.__b = 0;
0482     __u.__t     = __v;
0483     return __u.__s.__a ^ __u.__s.__b;
0484 #else
0485     return __scalar_hash<long double>::operator()(__v);
0486 #endif
0487   }
0488 };
0489
0490 template <class _Tp, bool = is_enum<_Tp>::value>
0491 struct _LIBCPP_TEMPLATE_VIS __enum_hash : public __unary_function<_Tp, size_t> {
0492   _LIBCPP_HIDE_FROM_ABI size_t operator()(_Tp __v) const _NOEXCEPT {
0493     typedef typename underlying_type<_Tp>::type type;
0494     return hash<type>()(static_cast<type>(__v));
0495   }
0496 };
0497 template <class _Tp>
0498 struct _LIBCPP_TEMPLATE_VIS __enum_hash<_Tp, false> {
0499   __enum_hash()                              = delete;
0500   __enum_hash(__enum_hash const&)            = delete;
0501   __enum_hash& operator=(__enum_hash const&) = delete;
0502 };
0503
0504 template <class _Tp>
0505 struct _LIBCPP_TEMPLATE_VIS hash : public __enum_hash<_Tp> {};
0506
0507 #if _LIBCPP_STD_VER >= 17
0508
0509 template <>
0510 struct _LIBCPP_TEMPLATE_VIS hash<nullptr_t> : public __unary_function<nullptr_t, size_t> {
0511   _LIBCPP_HIDE_FROM_ABI size_t operator()(nullptr_t) const _NOEXCEPT { return 662607004ull; }
0512 };
0513 #endif
0514
0515 #ifndef _LIBCPP_CXX03_LANG
0516 template <class _Key, class _Hash>
0517 using __check_hash_requirements _LIBCPP_NODEBUG =
0518     integral_constant<bool,
0519                       is_copy_constructible<_Hash>::value && is_move_constructible<_Hash>::value &&
0520                           __invokable_r<size_t, _Hash, _Key const&>::value >;
0521
0522 template <class _Key, class _Hash = hash<_Key> >
0523 using __has_enabled_hash _LIBCPP_NODEBUG =
0524     integral_constant<bool, __check_hash_requirements<_Key, _Hash>::value && is_default_constructible<_Hash>::value >;
0525
0526 #  if _LIBCPP_STD_VER >= 17
0527 template <class _Type, class>
0528 using __enable_hash_helper_imp _LIBCPP_NODEBUG = _Type;
0529
0530 template <class _Type, class... _Keys>
0531 using __enable_hash_helper _LIBCPP_NODEBUG =
0532     __enable_hash_helper_imp<_Type, __enable_if_t<__all<__has_enabled_hash<_Keys>::value...>::value> >;
0533 #  else
0534 template <class _Type, class...>
0535 using __enable_hash_helper _LIBCPP_NODEBUG = _Type;
0536 #  endif
0537
0538 #endif // !_LIBCPP_CXX03_LANG
0539
0540 _LIBCPP_END_NAMESPACE_STD
0541
0542 #endif // _LIBCPP___CXX03___FUNCTIONAL_HASH_H