libcxx/include/__memory/aligned_alloc.h

   1 //===----------------------------------------------------------------------===//
   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 _LIBCPP___MEMORY_ALIGNED_ALLOC_H
  10 #define _LIBCPP___MEMORY_ALIGNED_ALLOC_H
  11
  12 #include <__config>
  13 #include <cstdlib>
  14
  15 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  16 #  pragma GCC system_header
  17 #endif
  18
  19 _LIBCPP_BEGIN_NAMESPACE_STD
  20
  21 #if _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
  22
  23 // Low-level helpers to call the aligned allocation and deallocation functions
  24 // on the target platform. This is used to implement libc++'s own memory
  25 // allocation routines -- if you need to allocate memory inside the library,
  26 // chances are that you want to use `__libcpp_allocate` instead.
  27 //
  28 // Returns the allocated memory, or `nullptr` on failure.
  29 inline _LIBCPP_HIDE_FROM_ABI void* __libcpp_aligned_alloc(std::size_t __alignment, std::size_t __size) {
  30 #  if defined(_LIBCPP_MSVCRT_LIKE)
  31   return ::_aligned_malloc(__size, __alignment);
  32 #  elif _LIBCPP_STD_VER >= 17 && _LIBCPP_HAS_C11_ALIGNED_ALLOC
  33   // aligned_alloc() requires that __size is a multiple of __alignment,
  34   // but for C++ [new.delete.general], only states "if the value of an
  35   // alignment argument passed to any of these functions is not a valid
  36   // alignment value, the behavior is undefined".
  37   // To handle calls such as ::operator new(1, std::align_val_t(128)), we
  38   // round __size up to the next multiple of __alignment.
  39   size_t __rounded_size = (__size + __alignment - 1) & ~(__alignment - 1);
  40   // Rounding up could have wrapped around to zero, so we have to add another
  41   // max() ternary to the actual call site to avoid succeeded in that case.
  42   return ::aligned_alloc(__alignment, __size > __rounded_size ? __size : __rounded_size);
  43 #  else
  44   void* __result = nullptr;
  45   (void)::posix_memalign(&__result, __alignment, __size);
  46   // If posix_memalign fails, __result is unmodified so we still return `nullptr`.
  47   return __result;
  48 #  endif
  49 }
  50
  51 inline _LIBCPP_HIDE_FROM_ABI void __libcpp_aligned_free(void* __ptr) {
  52 #  if defined(_LIBCPP_MSVCRT_LIKE)
  53   ::_aligned_free(__ptr);
  54 #  else
  55   ::free(__ptr);
  56 #  endif
  57 }
  58
  59 #endif // _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
  60
  61 _LIBCPP_END_NAMESPACE_STD
  62
  63 #endif // _LIBCPP___MEMORY_ALIGNED_ALLOC_H