[libc-commits] [libc] [libc] [search] implement hcreate(_r)/hsearch(_r)/hdestroy(_r) (PR #73469)

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+//===-- HashTable BitMasks --------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H
+#define LLVM_LIBC_SRC___SUPPORT_HASHTABLE_BITMASK_H
+
+#include "src/__support/bit.h"
+#include <stddef.h> // size_t
+#include <stdint.h> // uint8_t, uint64_t
+
+namespace LIBC_NAMESPACE {
+namespace internal {
+
+// Implementations of the bitmask.
+// The backend word type may vary depending on different microarchitectures.
+// For example, with X86 SSE2, the bitmask is just the 16bit unsigned integer
+// corresponding to lanes in a SIMD register.
+//
+// Notice that this implementation is simplified from traditional swisstable:
+// since we do not support deletion, we only need to care about if the highest
+// bit is set or not:
+// =============================
+// | Slot Status |   Bitmask   |
+// =============================
+// |  Available  | 0b1xxx'xxxx |
+// |  Occupied   | 0b0xxx'xxxx |
+// =============================
+template <typename T, T WORD_MASK, size_t WORD_STRIDE> struct BitMaskAdaptor {
+  // A masked constant whose bits are all set.
+  constexpr static inline T MASK = WORD_MASK;
+  // A stride in the bitmask may use multiple bits.
+  constexpr static inline size_t STRIDE = WORD_STRIDE;
+
+  T word;
+
+  // Check if any bit is set inside the word.
+  bool any_bit_set() const { return word != 0; }
+
+  // Count trailing zeros with respect to stride. (Assume the bitmask is none
+  // zero.)
+  size_t lowest_set_bit_nonzero() const {
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lntue wrote:

I think you can mark these 2 methods `constexpr`.

https://github.com/llvm/llvm-project/pull/73469