[v4,05/22] libcamera: base: cxx20: Add `has_single_bit()`
diff mbox series

Message ID 20260106165754.1759831-6-barnabas.pocze@ideasonboard.com
State New
Headers show
Series
  • libcamera: Add `MetadataList`
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Commit Message

Barnabás Pőcze Jan. 6, 2026, 4:57 p.m. UTC 
`has_single_bit()` checks if the given unsigned integer has a single
bit set, that is, whether the number is a power of two or not.

Not all requirements of the C++20 standard are implemented.

See https://en.cppreference.com/w/cpp/numeric/has_single_bit

Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
---
 include/libcamera/base/internal/cxx20.h | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Comments

Jacopo Mondi Jan. 12, 2026, 9:39 a.m. UTC | #1 
Hi Barnabás

On Tue, Jan 06, 2026 at 05:57:37PM +0100, Barnabás Pőcze wrote:
> `has_single_bit()` checks if the given unsigned integer has a single
> bit set, that is, whether the number is a power of two or not.
>
> Not all requirements of the C++20 standard are implemented.
>
> See https://en.cppreference.com/w/cpp/numeric/has_single_bit
>
> Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
> Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

Do you think we can switch to c++20 and then re-apply the series on
top to remove these patches ?

> ---
>  include/libcamera/base/internal/cxx20.h | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/include/libcamera/base/internal/cxx20.h b/include/libcamera/base/internal/cxx20.h
> index 1f4caf56f..d47168a70 100644
> --- a/include/libcamera/base/internal/cxx20.h
> +++ b/include/libcamera/base/internal/cxx20.h
> @@ -7,6 +7,8 @@
>
>  #pragma once
>
> +#include <type_traits>
> +
>  /**
>   * \internal
>   * \file cxx20.h
> @@ -39,4 +41,18 @@ template<typename T> struct type_identity {
>   */
>  template<typename T> using type_identity_t = typename type_identity<T>::type;
>
> +/**
> + * \internal
> + * \brief std::has_single_bit()
> + *
> + * Implementation of std::has_single_bit() for C++17.
> + */
> +template<typename T>
> +constexpr bool has_single_bit(T x) noexcept
> +{
> +	static_assert(std::is_unsigned_v<T>);
> +
> +	return x != 0 && (x & (x - 1)) == 0;
> +}
> +
>  } /* namespace libcamera::internal::cxx20 */
> --
> 2.52.0
>

Patch
diff mbox series 

diff --git a/include/libcamera/base/internal/cxx20.h b/include/libcamera/base/internal/cxx20.h
index 1f4caf56f..d47168a70 100644
--- a/include/libcamera/base/internal/cxx20.h
+++ b/include/libcamera/base/internal/cxx20.h
@@ -7,6 +7,8 @@ 
 
 #pragma once
 
+#include <type_traits>
+
 /**
  * \internal
  * \file cxx20.h
@@ -39,4 +41,18 @@  template<typename T> struct type_identity {
  */
 template<typename T> using type_identity_t = typename type_identity<T>::type;
 
+/**
+ * \internal
+ * \brief std::has_single_bit()
+ *
+ * Implementation of std::has_single_bit() for C++17.
+ */
+template<typename T>
+constexpr bool has_single_bit(T x) noexcept
+{
+	static_assert(std::is_unsigned_v<T>);
+
+	return x != 0 && (x & (x - 1)) == 0;
+}
+
 } /* namespace libcamera::internal::cxx20 */