[libc][NFC] Use STL case for bitset and simplify implementation

1 files changed, 40 insertions, 0 deletions

diff --git a/libc/src/__support/CPP/bitset.h b/libc/src/__support/CPP/bitset.h
new file mode 100644
index 000000000000..0791e26d2c90
--- /dev/null
+++ b/libc/src/__support/CPP/bitset.h
@@ -0,0 +1,40 @@
+//===-- A self contained equivalent of std::bitset --------------*- 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_CPP_BITSET_H
+#define LLVM_LIBC_SRC_SUPPORT_CPP_BITSET_H
+
+#include <stddef.h> // For size_t.
+
+namespace __llvm_libc::cpp {
+
+template <size_t NumberOfBits> struct bitset {
+  static_assert(NumberOfBits != 0,
+                "Cannot create a __llvm_libc::cpp::bitset of size 0.");
+
+  constexpr void set(size_t Index) {
+    Data[Index / BITS_PER_UNIT] |= mask(Index);
+  }
+
+  constexpr bool test(size_t Index) const {
+    return Data[Index / BITS_PER_UNIT] & mask(Index);
+  }
+
+private:
+  static constexpr size_t BITS_PER_BYTE = 8;
+  static constexpr size_t BITS_PER_UNIT = BITS_PER_BYTE * sizeof(size_t);
+
+  static inline size_t mask(size_t Index) {
+    return size_t{1} << (Index % BITS_PER_UNIT);
+  }
+  size_t Data[(NumberOfBits + BITS_PER_UNIT - 1) / BITS_PER_UNIT] = {0};
+};
+
+} // namespace __llvm_libc::cpp
+
+#endif // LLVM_LIBC_SRC_SUPPORT_CPP_BITSET_H