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.. meta::
  :description: Documents cuda::std::bit in libhipcxx, covering bit manipulation functions such as popcount, rotl, rotr, and bit_width in host and device code.
  :keywords: libhipcxx, ROCm, HIP, C++, bit manipulation, popcount, bitwise, nodiscard

.. _libcudacxx-standard-api-numerics-bit:

``<cuda/std/bit>``
==================

This page documents ``<cuda/std/bit>`` in libhipcxx, which provides the C++ Standard Library bit manipulation
functions, such as ``popcount``, ``rotl``, ``rotr``, and ``bit_width``, in host and device code.

Notes
-----

- All functions are marked ``[[nodiscard]]`` and ``noexcept``.
- All functions support 128-bit integer types.
- ``bit_ceil()`` checks for overflow in debug mode.
- ``rotl()/rotr()`` checks for invalid count value (``INT_MIN``) in debug mode.
- The functions are ``constexpr``: for compile-time inputs libhipcxx evaluates them with a portable
  implementation, so the compiler folds them. For runtime inputs in device code it dispatches to the HIP device
  intrinsics, such as ``__popc`` for ``popcount()`` and ``__clz`` for ``countl_zero()``, while ``byteswap()`` uses
  ``__builtin_bswap32``.