1 //===-- HashTable BitMasks --------------------------------------*- C++ -*-===// 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 LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H 10 #define LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H 11 12 #include "src/__support/CPP/bit.h" 13 #include "src/__support/macros/properties/cpu_features.h" 14 #include <stddef.h> // size_t 15 #include <stdint.h> // uint8_t, uint64_t 16 17 namespace LIBC_NAMESPACE { 18 namespace internal { 19 20 // Implementations of the bitmask. 21 // The backend word type may vary depending on different microarchitectures. 22 // For example, with X86 SSE2, the bitmask is just the 16bit unsigned integer 23 // corresponding to lanes in a SIMD register. 24 // 25 // Notice that this implementation is simplified from traditional swisstable: 26 // since we do not support deletion, we only need to care about if the highest 27 // bit is set or not: 28 // ============================= 29 // | Slot Status | Bitmask | 30 // ============================= 31 // | Available | 0b1xxx'xxxx | 32 // | Occupied | 0b0xxx'xxxx | 33 // ============================= 34 template <typename T, size_t WORD_STRIDE> struct BitMaskAdaptor { 35 // A stride in the bitmask may use multiple bits. 36 LIBC_INLINE_VAR constexpr static size_t STRIDE = WORD_STRIDE; 37 38 T word; 39 40 // Check if any bit is set inside the word. any_bit_setBitMaskAdaptor41 LIBC_INLINE constexpr bool any_bit_set() const { return word != 0; } 42 43 // Count trailing zeros with respect to stride. (Assume the bitmask is none 44 // zero.) lowest_set_bit_nonzeroBitMaskAdaptor45 LIBC_INLINE constexpr size_t lowest_set_bit_nonzero() const { 46 return cpp::countr_zero<T>(word) / WORD_STRIDE; 47 } 48 }; 49 50 // Not all bitmasks are iterable --- only those who has only MSB set in each 51 // lane. Hence, we make the types nomially different to distinguish them. 52 template <class BitMask> struct IteratableBitMaskAdaptor : public BitMask { 53 // Use the bitmask as an iterator. Update the state and return current lowest 54 // set bit. To make the bitmask iterable, each stride must contain 0 or exact 55 // 1 set bit. remove_lowest_bitIteratableBitMaskAdaptor56 LIBC_INLINE void remove_lowest_bit() { 57 // Remove the last set bit inside the word: 58 // word = 011110100 (original value) 59 // word - 1 = 011110011 (invert all bits up to the last set bit) 60 // word & (word - 1) = 011110000 (value with the last bit cleared) 61 this->word = this->word & (this->word - 1); 62 } 63 using value_type = size_t; 64 using iterator = BitMask; 65 using const_iterator = BitMask; 66 LIBC_INLINE size_t operator*() const { 67 return this->lowest_set_bit_nonzero(); 68 } 69 LIBC_INLINE IteratableBitMaskAdaptor &operator++() { 70 this->remove_lowest_bit(); 71 return *this; 72 } beginIteratableBitMaskAdaptor73 LIBC_INLINE IteratableBitMaskAdaptor begin() { return *this; } endIteratableBitMaskAdaptor74 LIBC_INLINE IteratableBitMaskAdaptor end() { return {BitMask{0}}; } 75 LIBC_INLINE bool operator==(const IteratableBitMaskAdaptor &other) { 76 return this->word == other.word; 77 } 78 LIBC_INLINE bool operator!=(const IteratableBitMaskAdaptor &other) { 79 return this->word != other.word; 80 } 81 }; 82 83 } // namespace internal 84 } // namespace LIBC_NAMESPACE 85 86 #if defined(LIBC_TARGET_CPU_HAS_SSE2) && defined(__LIBC_EXPLICIT_SIMD_OPT) 87 #include "sse2/bitmask_impl.inc" 88 #else 89 #include "generic/bitmask_impl.inc" 90 #endif 91 92 #endif // LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H 93