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Edit File: pycore_bitutils.h
/* Bit and bytes utilities. Bytes swap functions, reverse order of bytes: - _Py_bswap16(uint16_t) - _Py_bswap32(uint32_t) - _Py_bswap64(uint64_t) */ #ifndef Py_INTERNAL_BITUTILS_H #define Py_INTERNAL_BITUTILS_H #ifdef __cplusplus extern "C" { #endif #ifndef Py_BUILD_CORE # error "this header requires Py_BUILD_CORE define" #endif #if defined(__GNUC__) \ && ((__GNUC__ >= 5) || (__GNUC__ == 4) && (__GNUC_MINOR__ >= 8)) /* __builtin_bswap16() is available since GCC 4.8, __builtin_bswap32() is available since GCC 4.3, __builtin_bswap64() is available since GCC 4.3. */ # define _PY_HAVE_BUILTIN_BSWAP #endif #ifdef _MSC_VER /* Get _byteswap_ushort(), _byteswap_ulong(), _byteswap_uint64() */ # include <intrin.h> #endif static inline uint16_t _Py_bswap16(uint16_t word) { #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap16) return __builtin_bswap16(word); #elif defined(_MSC_VER) Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned short)); return _byteswap_ushort(word); #else // Portable implementation which doesn't rely on circular bit shift return ( ((word & UINT16_C(0x00FF)) << 8) | ((word & UINT16_C(0xFF00)) >> 8)); #endif } static inline uint32_t _Py_bswap32(uint32_t word) { #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap32) return __builtin_bswap32(word); #elif defined(_MSC_VER) Py_BUILD_ASSERT(sizeof(word) == sizeof(unsigned long)); return _byteswap_ulong(word); #else // Portable implementation which doesn't rely on circular bit shift return ( ((word & UINT32_C(0x000000FF)) << 24) | ((word & UINT32_C(0x0000FF00)) << 8) | ((word & UINT32_C(0x00FF0000)) >> 8) | ((word & UINT32_C(0xFF000000)) >> 24)); #endif } static inline uint64_t _Py_bswap64(uint64_t word) { #if defined(_PY_HAVE_BUILTIN_BSWAP) || _Py__has_builtin(__builtin_bswap64) return __builtin_bswap64(word); #elif defined(_MSC_VER) return _byteswap_uint64(word); #else // Portable implementation which doesn't rely on circular bit shift return ( ((word & UINT64_C(0x00000000000000FF)) << 56) | ((word & UINT64_C(0x000000000000FF00)) << 40) | ((word & UINT64_C(0x0000000000FF0000)) << 24) | ((word & UINT64_C(0x00000000FF000000)) << 8) | ((word & UINT64_C(0x000000FF00000000)) >> 8) | ((word & UINT64_C(0x0000FF0000000000)) >> 24) | ((word & UINT64_C(0x00FF000000000000)) >> 40) | ((word & UINT64_C(0xFF00000000000000)) >> 56)); #endif } // Population count: count the number of 1's in 'x' // (number of bits set to 1), also known as the hamming weight. // // Implementation note. CPUID is not used, to test if x86 POPCNT instruction // can be used, to keep the implementation simple. For example, Visual Studio // __popcnt() is not used this reason. The clang and GCC builtin function can // use the x86 POPCNT instruction if the target architecture has SSE4a or // newer. static inline int _Py_popcount32(uint32_t x) { #if (defined(__clang__) || defined(__GNUC__)) #if SIZEOF_INT >= 4 Py_BUILD_ASSERT(sizeof(x) <= sizeof(unsigned int)); return __builtin_popcount(x); #else // The C standard guarantees that unsigned long will always be big enough // to hold a uint32_t value without losing information. Py_BUILD_ASSERT(sizeof(x) <= sizeof(unsigned long)); return __builtin_popcountl(x); #endif #else // 32-bit SWAR (SIMD Within A Register) popcount // Binary: 0 1 0 1 ... const uint32_t M1 = 0x55555555; // Binary: 00 11 00 11. .. const uint32_t M2 = 0x33333333; // Binary: 0000 1111 0000 1111 ... const uint32_t M4 = 0x0F0F0F0F; // Put count of each 2 bits into those 2 bits x = x - ((x >> 1) & M1); // Put count of each 4 bits into those 4 bits x = (x & M2) + ((x >> 2) & M2); // Put count of each 8 bits into those 8 bits x = (x + (x >> 4)) & M4; // Sum of the 4 byte counts. // Take care when considering changes to the next line. Portability and // correctness are delicate here, thanks to C's "integer promotions" (C99 // §6.3.1.1p2). On machines where the `int` type has width greater than 32 // bits, `x` will be promoted to an `int`, and following C's "usual // arithmetic conversions" (C99 §6.3.1.8), the multiplication will be // performed as a multiplication of two `unsigned int` operands. In this // case it's critical that we cast back to `uint32_t` in order to keep only // the least significant 32 bits. On machines where the `int` type has // width no greater than 32, the multiplication is of two 32-bit unsigned // integer types, and the (uint32_t) cast is a no-op. In both cases, we // avoid the risk of undefined behaviour due to overflow of a // multiplication of signed integer types. return (uint32_t)(x * 0x01010101U) >> 24; #endif } // Return the index of the most significant 1 bit in 'x'. This is the smallest // integer k such that x < 2**k. Equivalent to floor(log2(x)) + 1 for x != 0. static inline int _Py_bit_length(unsigned long x) { #if (defined(__clang__) || defined(__GNUC__)) if (x != 0) { // __builtin_clzl() is available since GCC 3.4. // Undefined behavior for x == 0. return (int)sizeof(unsigned long) * 8 - __builtin_clzl(x); } else { return 0; } #elif defined(_MSC_VER) // _BitScanReverse() is documented to search 32 bits. Py_BUILD_ASSERT(sizeof(unsigned long) <= 4); unsigned long msb; if (_BitScanReverse(&msb, x)) { return (int)msb + 1; } else { return 0; } #else const int BIT_LENGTH_TABLE[32] = { 0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 }; int msb = 0; while (x >= 32) { msb += 6; x >>= 6; } msb += BIT_LENGTH_TABLE[x]; return msb; #endif } #ifdef __cplusplus } #endif #endif /* !Py_INTERNAL_BITUTILS_H */