[libc++] Introduce __bits
It has the low-level bit fiddling operations from bit. It eliminates a cyclic dependency between __bit_reference, bits, and vector. I want to exploit this in later patches.
Reviewed By: #libc, ldionne
Differential Revision: https://reviews.llvm.org/D94908
GitOrigin-RevId: b973e2e2f27ede7a70d470ea537f1901759d239d
diff --git a/include/__bits b/include/__bits
new file mode 100644
index 0000000..0d321da
--- /dev/null
+++ b/include/__bits
@@ -0,0 +1,146 @@
+// -*- 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 _LIBCPP___BITS
+#define _LIBCPP___BITS
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_COMPILER_MSVC
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_ctz(unsigned __x) _NOEXCEPT { return __builtin_ctz(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_ctz(unsigned long __x) _NOEXCEPT { return __builtin_ctzl(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_ctz(unsigned long long __x) _NOEXCEPT { return __builtin_ctzll(__x); }
+
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_clz(unsigned __x) _NOEXCEPT { return __builtin_clz(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_clz(unsigned long __x) _NOEXCEPT { return __builtin_clzl(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_clz(unsigned long long __x) _NOEXCEPT { return __builtin_clzll(__x); }
+
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_popcount(unsigned __x) _NOEXCEPT { return __builtin_popcount(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_popcount(unsigned long __x) _NOEXCEPT { return __builtin_popcountl(__x); }
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
+int __libcpp_popcount(unsigned long long __x) _NOEXCEPT { return __builtin_popcountll(__x); }
+
+#else // _LIBCPP_COMPILER_MSVC
+
+// Precondition: __x != 0
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_ctz(unsigned __x) {
+ static_assert(sizeof(unsigned) == sizeof(unsigned long), "");
+ static_assert(sizeof(unsigned long) == 4, "");
+ unsigned long __where;
+ if (_BitScanForward(&__where, __x))
+ return static_cast<int>(__where);
+ return 32;
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_ctz(unsigned long __x) {
+ static_assert(sizeof(unsigned long) == sizeof(unsigned), "");
+ return __ctz(static_cast<unsigned>(__x));
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_ctz(unsigned long long __x) {
+ unsigned long __where;
+#if defined(_LIBCPP_HAS_BITSCAN64)
+ (defined(_M_AMD64) || defined(__x86_64__))
+ if (_BitScanForward64(&__where, __x))
+ return static_cast<int>(__where);
+#else
+ // Win32 doesn't have _BitScanForward64 so emulate it with two 32 bit calls.
+ if (_BitScanForward(&__where, static_cast<unsigned long>(__x)))
+ return static_cast<int>(__where);
+ if (_BitScanForward(&__where, static_cast<unsigned long>(__x >> 32)))
+ return static_cast<int>(__where + 32);
+#endif
+ return 64;
+}
+
+// Precondition: __x != 0
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_clz(unsigned __x) {
+ static_assert(sizeof(unsigned) == sizeof(unsigned long), "");
+ static_assert(sizeof(unsigned long) == 4, "");
+ unsigned long __where;
+ if (_BitScanReverse(&__where, __x))
+ return static_cast<int>(31 - __where);
+ return 32; // Undefined Behavior.
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_clz(unsigned long __x) {
+ static_assert(sizeof(unsigned) == sizeof(unsigned long), "");
+ return __libcpp_clz(static_cast<unsigned>(__x));
+}
+
+inline _LIBCPP_INLINE_VISIBILITY
+int __libcpp_clz(unsigned long long __x) {
+ unsigned long __where;
+#if defined(_LIBCPP_HAS_BITSCAN64)
+ if (_BitScanReverse64(&__where, __x))
+ return static_cast<int>(63 - __where);
+#else
+ // Win32 doesn't have _BitScanReverse64 so emulate it with two 32 bit calls.
+ if (_BitScanReverse(&__where, static_cast<unsigned long>(__x >> 32)))
+ return static_cast<int>(63 - (__where + 32));
+ if (_BitScanReverse(&__where, static_cast<unsigned long>(__x)))
+ return static_cast<int>(63 - __where);
+#endif
+ return 64; // Undefined Behavior.
+}
+
+inline _LIBCPP_INLINE_VISIBILITY int __libcpp_popcount(unsigned __x) {
+ static_assert(sizeof(unsigned) == 4, "");
+ return __popcnt(__x);
+}
+
+inline _LIBCPP_INLINE_VISIBILITY int __libcpp_popcount(unsigned long __x) {
+ static_assert(sizeof(unsigned long) == 4, "");
+ return __popcnt(__x);
+}
+
+inline _LIBCPP_INLINE_VISIBILITY int __libcpp_popcount(unsigned long long __x) {
+ static_assert(sizeof(unsigned long long) == 8, "");
+ return __popcnt64(__x);
+}
+
+#endif // _LIBCPP_COMPILER_MSVC
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP__BITS