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| 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/config.h" |
| 14 | #include "src/__support/macros/properties/cpu_features.h" |
| 15 | #include <stddef.h> // size_t |
| 16 | #include <stdint.h> // uint8_t, uint64_t |
| 17 | |
| 18 | namespace LIBC_NAMESPACE_DECL { |
| 19 | namespace internal { |
| 20 | |
| 21 | // Implementations of the bitmask. |
| 22 | // The backend word type may vary depending on different microarchitectures. |
| 23 | // For example, with X86 SSE2, the bitmask is just the 16bit unsigned integer |
| 24 | // corresponding to lanes in a SIMD register. |
| 25 | // |
| 26 | // Notice that this implementation is simplified from traditional swisstable: |
| 27 | // since we do not support deletion, we only need to care about if the highest |
| 28 | // bit is set or not: |
| 29 | // ============================= |
| 30 | // | Slot Status | Bitmask | |
| 31 | // ============================= |
| 32 | // | Available | 0b1xxx'xxxx | |
| 33 | // | Occupied | 0b0xxx'xxxx | |
| 34 | // ============================= |
| 35 | template <typename T, size_t WORD_STRIDE> struct BitMaskAdaptor { |
| 36 | // A stride in the bitmask may use multiple bits. |
| 37 | LIBC_INLINE_VAR constexpr static size_t STRIDE = WORD_STRIDE; |
| 38 | |
| 39 | T word; |
| 40 | |
| 41 | // Check if any bit is set inside the word. |
| 42 | LIBC_INLINE constexpr bool any_bit_set() const { return word != 0; } |
| 43 | |
| 44 | // Count trailing zeros with respect to stride. (Assume the bitmask is none |
| 45 | // zero.) |
| 46 | LIBC_INLINE constexpr size_t lowest_set_bit_nonzero() const { |
| 47 | return cpp::countr_zero<T>(word) / WORD_STRIDE; |
| 48 | } |
| 49 | }; |
| 50 | |
| 51 | // Not all bitmasks are iterable --- only those who has only MSB set in each |
| 52 | // lane. Hence, we make the types nomially different to distinguish them. |
| 53 | template <class BitMask> struct IteratableBitMaskAdaptor : public BitMask { |
| 54 | // Use the bitmask as an iterator. Update the state and return current lowest |
| 55 | // set bit. To make the bitmask iterable, each stride must contain 0 or exact |
| 56 | // 1 set bit. |
| 57 | LIBC_INLINE void remove_lowest_bit() { |
| 58 | // Remove the last set bit inside the word: |
| 59 | // word = 011110100 (original value) |
| 60 | // word - 1 = 011110011 (invert all bits up to the last set bit) |
| 61 | // word & (word - 1) = 011110000 (value with the last bit cleared) |
| 62 | this->word = this->word & (this->word - 1); |
| 63 | } |
| 64 | using value_type = size_t; |
| 65 | using iterator = BitMask; |
| 66 | using const_iterator = BitMask; |
| 67 | LIBC_INLINE size_t operator*() const { |
| 68 | return this->lowest_set_bit_nonzero(); |
| 69 | } |
| 70 | LIBC_INLINE IteratableBitMaskAdaptor &operator++() { |
| 71 | this->remove_lowest_bit(); |
| 72 | return *this; |
| 73 | } |
| 74 | LIBC_INLINE IteratableBitMaskAdaptor begin() { return *this; } |
| 75 | LIBC_INLINE IteratableBitMaskAdaptor end() { return {BitMask{0}}; } |
| 76 | LIBC_INLINE bool operator==(const IteratableBitMaskAdaptor &other) { |
| 77 | return this->word == other.word; |
| 78 | } |
| 79 | LIBC_INLINE bool operator!=(const IteratableBitMaskAdaptor &other) { |
| 80 | return this->word != other.word; |
| 81 | } |
| 82 | }; |
| 83 | |
| 84 | } // namespace internal |
| 85 | } // namespace LIBC_NAMESPACE_DECL |
| 86 | |
| 87 | #if defined(LIBC_TARGET_CPU_HAS_SSE2) && defined(__LIBC_EXPLICIT_SIMD_OPT) |
| 88 | #include "sse2/bitmask_impl.inc" |
| 89 | #else |
| 90 | #include "generic/bitmask_impl.inc" |
| 91 | #endif |
| 92 | |
| 93 | #endif // LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H |
| 94 |
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