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The C and C++ Include Header Files
/usr/include/python3.10/internal/pycore_bitutils.h
$ cat -n /usr/include/python3.10/internal/pycore_bitutils.h 1 /* Bit and bytes utilities. 2 3 Bytes swap functions, reverse order of bytes: 4 5 - _Py_bswap16(uint16_t) 6 - _Py_bswap32(uint32_t) 7 - _Py_bswap64(uint64_t) 8 */ 9 10 #ifndef Py_INTERNAL_BITUTILS_H 11 #define Py_INTERNAL_BITUTILS_H 12 #ifdef __cplusplus 13 extern "C" { 14 #endif 15 16 #ifndef Py_BUILD_CORE 17 # error "this header requires Py_BUILD_CORE define" 18 #endif 19 20 #if defined(__GNUC__) \ 21 && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8)) 22 /* __builtin_bswap16() is available since GCC 4.8, 23 __builtin_bswap32() is available since GCC 4.3, 24 __builtin_bswap64() is available since GCC 4.3. */ 25 # define _PY_HAVE_BUILTIN_BSWAP 26 #endif 27 28 #ifdef _MSC_VER 29 /* Get _byteswap_ushort(), _byteswap_ulong(), _byteswap_uint64() */ 30 # include <intrin.h> 31 #endif 32 33 static inline uint16_t 34 _Py_bswap16(uint16_t word) 35 { 36 #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap16) 37 return __builtin_bswap16(word); 38 #elif defined(_MSC_VER) 39 Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned short)); 40 return _byteswap_ushort(word); 41 #else 42 // Portable implementation which doesn't rely on circular bit shift 43 return ( ((word & UINT16_C(0x00FF)) << 8) 44 | ((word & UINT16_C(0xFF00)) >> 8)); 45 #endif 46 } 47 48 static inline uint32_t 49 _Py_bswap32(uint32_t word) 50 { 51 #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap32) 52 return __builtin_bswap32(word); 53 #elif defined(_MSC_VER) 54 Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned long)); 55 return _byteswap_ulong(word); 56 #else 57 // Portable implementation which doesn't rely on circular bit shift 58 return ( ((word & UINT32_C(0x000000FF)) << 24) 59 | ((word & UINT32_C(0x0000FF00)) << 8) 60 | ((word & UINT32_C(0x00FF0000)) >> 8) 61 | ((word & UINT32_C(0xFF000000)) >> 24)); 62 #endif 63 } 64 65 static inline uint64_t 66 _Py_bswap64(uint64_t word) 67 { 68 #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap64) 69 return __builtin_bswap64(word); 70 #elif defined(_MSC_VER) 71 return _byteswap_uint64(word); 72 #else 73 // Portable implementation which doesn't rely on circular bit shift 74 return ( ((word & UINT64_C(0x00000000000000FF)) << 56) 75 | ((word & UINT64_C(0x000000000000FF00)) << 40) 76 | ((word & UINT64_C(0x0000000000FF0000)) << 24) 77 | ((word & UINT64_C(0x00000000FF000000)) << 8) 78 | ((word & UINT64_C(0x000000FF00000000)) >> 8) 79 | ((word & UINT64_C(0x0000FF0000000000)) >> 24) 80 | ((word & UINT64_C(0x00FF000000000000)) >> 40) 81 | ((word & UINT64_C(0xFF00000000000000)) >> 56)); 82 #endif 83 } 84 85 86 // Population count: count the number of 1's in 'x' 87 // (number of bits set to 1), also known as the hamming weight. 88 // 89 // Implementation note. CPUID is not used, to test if x86 POPCNT instruction 90 // can be used, to keep the implementation simple. For example, Visual Studio 91 // __popcnt() is not used this reason. The clang and GCC builtin function can 92 // use the x86 POPCNT instruction if the target architecture has SSE4a or 93 // newer. 94 static inline int 95 _Py_popcount32(uint32_t x) 96 { 97 #if (defined(__clang__) || defined(__GNUC__)) 98 99 #if SIZEOF_INT >= 4 100 Py_BUILD_ASSERT(sizeof(x) <= sizeof(unsigned int)); 101 return __builtin_popcount(x); 102 #else 103 // The C standard guarantees that unsigned long will always be big enough 104 // to hold a uint32_t value without losing information. 105 Py_BUILD_ASSERT(sizeof(x) <= sizeof(unsigned long)); 106 return __builtin_popcountl(x); 107 #endif 108 109 #else 110 // 32-bit SWAR (SIMD Within A Register) popcount 111 112 // Binary: 0 1 0 1 ... 113 const uint32_t M1 = 0x55555555; 114 // Binary: 00 11 00 11. .. 115 const uint32_t M2 = 0x33333333; 116 // Binary: 0000 1111 0000 1111 ... 117 const uint32_t M4 = 0x0F0F0F0F; 118 // 256**4 + 256**3 + 256**2 + 256**1 119 const uint32_t SUM = 0x01010101; 120 121 // Put count of each 2 bits into those 2 bits 122 x = x - ((x >> 1) & M1); 123 // Put count of each 4 bits into those 4 bits 124 x = (x & M2) + ((x >> 2) & M2); 125 // Put count of each 8 bits into those 8 bits 126 x = (x + (x >> 4)) & M4; 127 // Sum of the 4 byte counts 128 return (uint32_t)((uint64_t)x * (uint64_t)SUM) >> 24; 129 #endif 130 } 131 132 133 // Return the index of the most significant 1 bit in 'x'. This is the smallest 134 // integer k such that x < 2**k. Equivalent to floor(log2(x)) + 1 for x != 0. 135 static inline int 136 _Py_bit_length(unsigned long x) 137 { 138 #if (defined(__clang__) || defined(__GNUC__)) 139 if (x != 0) { 140 // __builtin_clzl() is available since GCC 3.4. 141 // Undefined behavior for x == 0. 142 return (int)sizeof(unsigned long) * 8 - __builtin_clzl(x); 143 } 144 else { 145 return 0; 146 } 147 #elif defined(_MSC_VER) 148 // _BitScanReverse() is documented to search 32 bits. 149 Py_BUILD_ASSERT(sizeof(unsigned long) <= 4); 150 unsigned long msb; 151 if (_BitScanReverse(&msb, x)) { 152 return (int)msb + 1; 153 } 154 else { 155 return 0; 156 } 157 #else 158 const int BIT_LENGTH_TABLE[32] = { 159 0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 160 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 161 }; 162 int msb = 0; 163 while (x >= 32) { 164 msb += 6; 165 x >>= 6; 166 } 167 msb += BIT_LENGTH_TABLE[x]; 168 return msb; 169 #endif 170 } 171 172 173 #ifdef __cplusplus 174 } 175 #endif 176 #endif /* !Py_INTERNAL_BITUTILS_H */
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