src/__support/CPP/Bit.h

//===-- Freestanding version of bit_cast  -----------------------*- 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_SUPPORT_CPP_BIT_H
#define LLVM_LIBC_SUPPORT_CPP_BIT_H

namespace __llvm_libc {

#if defined __has_builtin
#if __has_builtin(__builtin_bit_cast)
#define LLVM_LIBC_HAS_BUILTIN_BIT_CAST
#endif
#endif

#if defined __has_builtin
#if __has_builtin(__builtin_memcpy_inline)
#define LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE
#endif
#endif

// This function guarantees the bitcast to be optimized away by the compiler for
// GCC >= 8 and Clang >= 6.
template <class To, class From> constexpr To bit_cast(const From &from) {
  static_assert(sizeof(To) == sizeof(From), "To and From must be of same size");
#if defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
  return __builtin_bit_cast(To, from);
#else
  To to;
  char *dst = reinterpret_cast<char *>(&to);
  const char *src = reinterpret_cast<const char *>(&from);
#if defined(LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE)
  __builtin_memcpy_inline(dst, src, sizeof(To));
#else
  for (unsigned i = 0; i < sizeof(To); ++i)
    dst[i] = src[i];
#endif // defined(LLVM_LIBC_HAS_BUILTIN_MEMCPY_INLINE)
  return to;
#endif // defined(LLVM_LIBC_HAS_BUILTIN_BIT_CAST)
}

} // namespace __llvm_libc

#endif // LLVM_LIBC_SUPPORT_CPP_BIT_H