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 <cstddef>
  14 #include <cstdlib>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 _LIBCPP_BEGIN_NAMESPACE_STD
  21
  22 #ifndef _LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
  23
  24 // Low-level helpers to call the aligned allocation and deallocation functions
  25 // on the target platform. This is used to implement libc++'s own memory
  26 // allocation routines -- if you need to allocate memory inside the library,
  27 // chances are that you want to use `__libcpp_allocate` instead.
  28 //
  29 // Returns the allocated memory, or `nullptr` on failure.
  30 inline _LIBCPP_HIDE_FROM_ABI
  31 void* __libcpp_aligned_alloc(std::size_t __alignment, std::size_t __size) {
  32 #  if defined(_LIBCPP_MSVCRT_LIKE)
  33     return ::_aligned_malloc(__size, __alignment);
  34 #  elif _LIBCPP_STD_VER >= 17 && !defined(_LIBCPP_HAS_NO_C11_ALIGNED_ALLOC)
  35     // aligned_alloc() requires that __size is a multiple of __alignment,
  36     // but for C++ [new.delete.general], only states "if the value of an
  37     // alignment argument passed to any of these functions is not a valid
  38     // alignment value, the behavior is undefined".
  39     // To handle calls such as ::operator new(1, std::align_val_t(128)), we
  40     // round __size up to the next multiple of __alignment.
  41     size_t __rounded_size = (__size + __alignment - 1) & ~(__alignment - 1);
  42     // Rounding up could have wrapped around to zero, so we have to add another
  43     // max() ternary to the actual call site to avoid succeeded in that case.
  44     return ::aligned_alloc(__alignment, __size > __rounded_size ? __size : __rounded_size);
  45 #  else
  46     void* __result = nullptr;
  47     (void)::posix_memalign(&__result, __alignment, __size);
  48     // If posix_memalign fails, __result is unmodified so we still return `nullptr`.
  49     return __result;
  50 #  endif
  51 }
  52
  53 inline _LIBCPP_HIDE_FROM_ABI
  54 void __libcpp_aligned_free(void* __ptr) {
  55 #if defined(_LIBCPP_MSVCRT_LIKE)
  56   ::_aligned_free(__ptr);
  57 #else
  58   ::free(__ptr);
  59 #endif
  60 }
  61
  62 #endif // !_LIBCPP_HAS_NO_LIBRARY_ALIGNED_ALLOCATION
  63
  64 _LIBCPP_END_NAMESPACE_STD
  65
  66 #endif // _LIBCPP___MEMORY_ALIGNED_ALLOC_H