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.. meta::
  :description: Learn about libhipcxx extensions to the C++ Standard Library.
  :keywords: libhipcxx, ROCm, HIP, C++, extensions, thread scope, atomic, synchronization, CUDA, AMD GPU

.. _libhipcxx-extensions:

********************************************
C++ Standard Library extensions in libhipcxx
********************************************

libhipcxx provides HIP C++ developers with familiar Standard Library utilities to improve
productivity and flatten the learning curve of HIP. However, there are many aspects of writing
high-performance HIP C++ code that cannot be expressed through purely Standard conforming APIs. For
these cases, libhipcxx also provides *extensions* of Standard Library utilities.

To use utilities that are extensions to Standard Library features, drop the ``std`` from both the
include path and namespace:

.. code-block:: cpp

    #include <cuda/atomic>

    cuda::atomic<int, cuda::thread_scope_device> x;

For a full explanation of the namespace hierarchy, see
:ref:`HIP-specific abstractions and namespaces <libhipcxx-hip-abstractions>`.

Available extensions
====================

libhipcxx provides extensions across synchronization, memory, math, and device-specific
functionality. The following table lists each extension category with its key APIs:

.. list-table::
   :widths: 25 45 30
   :header-rows: 1

   * - Extension
     - APIs
     - Notes
   * - Thread-scope synchronization
     - * ``cuda::atomic`` / ``hip::atomic``
       * ``cuda::atomic_ref`` / ``hip::atomic_ref``
     - ``cuda::thread_scope`` controls memory fence strength across thread, block, device, or system
   * - Functional utilities
     - * ``cuda::maximum`` / ``hip::maximum``
       * ``cuda::minimum`` / ``hip::minimum``
       * ``cuda::proclaim_return_type`` / ``hip::proclaim_return_type``
       * ``cuda::get_device_address`` / ``hip::get_device_address``
     -
   * - Math utilities
     - * ``cuda::ceil_div`` / ``hip::ceil_div``
       * ``cuda::round_up`` / ``hip::round_up``
       * ``cuda::round_down`` / ``hip::round_down``
       * ``cuda::ilog2`` / ``hip::ilog2``
       * ``cuda::ilog10`` / ``hip::ilog10``
     -
   * - Bit utilities
     - * ``cuda::bitmask`` / ``hip::bitmask``
       * ``cuda::bit_reverse`` / ``hip::bit_reverse``
       * ``cuda::bitfield_insert`` / ``hip::bitfield_insert``
       * ``cuda::bitfield_extract`` / ``hip::bitfield_extract``
     -
   * - Stream reference
     - * ``cuda::stream_ref`` / ``hip::stream_ref``
     - Type-safe wrapper around ``hipStream_t``
   * - Memory resources
     - * ``cuda::mr::resource`` / ``hip::mr::resource``
       * ``cuda::mr::resource_ref`` / ``hip::mr::resource_ref``
     - Experimental. Requires ``LIBCUDACXX_ENABLE_EXPERIMENTAL_MEMORY_RESOURCE``.

For per-API documentation, see the :ref:`Extended API reference <libcudacxx-extended-api>`.

Unsupported extensions
======================

Several extensions from the upstream libcudacxx project are not supported in libhipcxx because they
depend on NVIDIA hardware. These include:

- ``<cuda/latch>``, ``<cuda/barrier>``, ``<cuda/semaphore>``, ``<cuda/pipeline>`` — scoped
  synchronization primitives
- ``cuda::memcpy_async``, ``cuda::memcpy_async_tx``, ``cuda::aligned_size_t`` — asynchronous
  copies, which depend on ``<cuda/barrier>`` and ``<cuda/pipeline>``
- ``<cuda/annotated_ptr>`` — memory access properties for pointers
- ``cuda::discard_memory`` — available, but has no effect on AMD GPUs
- ``cuda::device::warp_shuffle_idx``, ``warp_shuffle_up``, ``warp_shuffle_down``,
  ``warp_shuffle_xor`` — warp shuffles, which are only compiled for NVIDIA PTX targets
- ``cuda::for_each_canceled_block`` — work stealing, which depends on NVIDIA hardware block
  cancellation. On AMD GPUs it invokes the function once for the current block.
- ``<cuda/ptx>`` — NVIDIA PTX instruction wrappers

For the complete list, see :ref:`Limitations and unsupported APIs <libhipcxx-limitations>`.