| Message ID | 20250721104622.1550908-6-barnabas.pocze@ideasonboard.com |
|---|---|
| State | New |
| Headers | show |
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| Related | show |
Hi Barnabás On Mon, Jul 21, 2025 at 12:46:05PM +0200, 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> > --- > include/libcamera/base/details/cxx20.h | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h > index 2d26db53e..8bf45ff11 100644 > --- a/include/libcamera/base/details/cxx20.h > +++ b/include/libcamera/base/details/cxx20.h > @@ -7,9 +7,19 @@ > > #pragma once > > +#include <type_traits> > + > namespace libcamera::details::cxx20 { > > template<typename T> struct type_identity { using type = T; }; > template<typename T> using type_identity_t = typename type_identity<T>::type; > > +template<typename T> > +constexpr bool has_single_bit(T x) noexcept > +{ > + static_assert(std::is_unsigned_v<T>); I was wondering if a compile time assertion is better than restricting the template substitution to unsigned int with std::enable_if<> but in the end the result is the same... > + > + return x != 0 && (x & (x - 1)) == 0; cppreference.com has a more "compact" return x && !(x & (x - 1)); Up to you! Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> > +} > + > } /* namespace libcamera::details::cxx20 */ > -- > 2.50.1 >
On Fri, Jul 25, 2025 at 03:04:46PM +0200, Jacopo Mondi wrote: > Hi Barnabás > > On Mon, Jul 21, 2025 at 12:46:05PM +0200, 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> > > --- > > include/libcamera/base/details/cxx20.h | 10 ++++++++++ > > 1 file changed, 10 insertions(+) > > > > diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h > > index 2d26db53e..8bf45ff11 100644 > > --- a/include/libcamera/base/details/cxx20.h > > +++ b/include/libcamera/base/details/cxx20.h > > @@ -7,9 +7,19 @@ > > > > #pragma once > > > > +#include <type_traits> > > + > > namespace libcamera::details::cxx20 { > > > > template<typename T> struct type_identity { using type = T; }; > > template<typename T> using type_identity_t = typename type_identity<T>::type; > > > > +template<typename T> > > +constexpr bool has_single_bit(T x) noexcept > > +{ > > + static_assert(std::is_unsigned_v<T>); > > I was wondering if a compile time assertion is better than restricting > the template substitution to unsigned int with std::enable_if<> but in > the end the result is the same... When there are no other template candidates they need to be considered, a static assertion will give better error messages. Can we add a std::is_integral check here to get closer to the C++20 requirements ? > > + > > + return x != 0 && (x & (x - 1)) == 0; > > cppreference.com has a more "compact" > > return x && !(x & (x - 1)); > > Up to you! > > Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> > > > +} > > + > > } /* namespace libcamera::details::cxx20 */
Hi 2025. 07. 27. 15:36 keltezéssel, Laurent Pinchart írta: > On Fri, Jul 25, 2025 at 03:04:46PM +0200, Jacopo Mondi wrote: >> Hi Barnabás >> >> On Mon, Jul 21, 2025 at 12:46:05PM +0200, 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> >>> --- >>> include/libcamera/base/details/cxx20.h | 10 ++++++++++ >>> 1 file changed, 10 insertions(+) >>> >>> diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h >>> index 2d26db53e..8bf45ff11 100644 >>> --- a/include/libcamera/base/details/cxx20.h >>> +++ b/include/libcamera/base/details/cxx20.h >>> @@ -7,9 +7,19 @@ >>> >>> #pragma once >>> >>> +#include <type_traits> >>> + >>> namespace libcamera::details::cxx20 { >>> >>> template<typename T> struct type_identity { using type = T; }; >>> template<typename T> using type_identity_t = typename type_identity<T>::type; >>> >>> +template<typename T> >>> +constexpr bool has_single_bit(T x) noexcept >>> +{ >>> + static_assert(std::is_unsigned_v<T>); >> >> I was wondering if a compile time assertion is better than restricting >> the template substitution to unsigned int with std::enable_if<> but in >> the end the result is the same... > > When there are no other template candidates they need to be considered, > a static assertion will give better error messages. > > Can we add a std::is_integral check here to get closer to the C++20 > requirements ? C++20 defines it only for some unsigned types. Could you clarify why `std::is_integral` would be needed? Regards, Barnabás Pőcze > >>> + >>> + return x != 0 && (x & (x - 1)) == 0; >> >> cppreference.com has a more "compact" >> >> return x && !(x & (x - 1)); >> >> Up to you! >> >> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> >> >>> +} >>> + >>> } /* namespace libcamera::details::cxx20 */ >
On Sun, Jul 27, 2025 at 07:19:22PM +0200, Barnabás Pőcze wrote: > 2025. 07. 27. 15:36 keltezéssel, Laurent Pinchart írta: > > On Fri, Jul 25, 2025 at 03:04:46PM +0200, Jacopo Mondi wrote: > >> On Mon, Jul 21, 2025 at 12:46:05PM +0200, 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> > >>> --- > >>> include/libcamera/base/details/cxx20.h | 10 ++++++++++ > >>> 1 file changed, 10 insertions(+) > >>> > >>> diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h > >>> index 2d26db53e..8bf45ff11 100644 > >>> --- a/include/libcamera/base/details/cxx20.h > >>> +++ b/include/libcamera/base/details/cxx20.h > >>> @@ -7,9 +7,19 @@ > >>> > >>> #pragma once > >>> > >>> +#include <type_traits> > >>> + > >>> namespace libcamera::details::cxx20 { > >>> > >>> template<typename T> struct type_identity { using type = T; }; > >>> template<typename T> using type_identity_t = typename type_identity<T>::type; > >>> > >>> +template<typename T> > >>> +constexpr bool has_single_bit(T x) noexcept > >>> +{ > >>> + static_assert(std::is_unsigned_v<T>); > >> > >> I was wondering if a compile time assertion is better than restricting > >> the template substitution to unsigned int with std::enable_if<> but in > >> the end the result is the same... > > > > When there are no other template candidates they need to be considered, > > a static assertion will give better error messages. > > > > Can we add a std::is_integral check here to get closer to the C++20 > > requirements ? > > C++20 defines it only for some unsigned types. Could you clarify why > `std::is_integral` would be needed? Hmmm I suppose std::is_unsigned implies std::is_integral ? Could we match the C++20 requirements to avoid accidental use of this function that would not work with the C++20 version when we'll switch to that standard ? > >>> + > >>> + return x != 0 && (x & (x - 1)) == 0; > >> > >> cppreference.com has a more "compact" > >> > >> return x && !(x & (x - 1)); > >> > >> Up to you! > >> > >> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> > >> > >>> +} > >>> + > >>> } /* namespace libcamera::details::cxx20 */
2025. 07. 27. 20:38 keltezéssel, Laurent Pinchart írta: > On Sun, Jul 27, 2025 at 07:19:22PM +0200, Barnabás Pőcze wrote: >> 2025. 07. 27. 15:36 keltezéssel, Laurent Pinchart írta: >>> On Fri, Jul 25, 2025 at 03:04:46PM +0200, Jacopo Mondi wrote: >>>> On Mon, Jul 21, 2025 at 12:46:05PM +0200, 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> >>>>> --- >>>>> include/libcamera/base/details/cxx20.h | 10 ++++++++++ >>>>> 1 file changed, 10 insertions(+) >>>>> >>>>> diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h >>>>> index 2d26db53e..8bf45ff11 100644 >>>>> --- a/include/libcamera/base/details/cxx20.h >>>>> +++ b/include/libcamera/base/details/cxx20.h >>>>> @@ -7,9 +7,19 @@ >>>>> >>>>> #pragma once >>>>> >>>>> +#include <type_traits> >>>>> + >>>>> namespace libcamera::details::cxx20 { >>>>> >>>>> template<typename T> struct type_identity { using type = T; }; >>>>> template<typename T> using type_identity_t = typename type_identity<T>::type; >>>>> >>>>> +template<typename T> >>>>> +constexpr bool has_single_bit(T x) noexcept >>>>> +{ >>>>> + static_assert(std::is_unsigned_v<T>); >>>> >>>> I was wondering if a compile time assertion is better than restricting >>>> the template substitution to unsigned int with std::enable_if<> but in >>>> the end the result is the same... >>> >>> When there are no other template candidates they need to be considered, >>> a static assertion will give better error messages. >>> >>> Can we add a std::is_integral check here to get closer to the C++20 >>> requirements ? >> >> C++20 defines it only for some unsigned types. Could you clarify why >> `std::is_integral` would be needed? > > Hmmm I suppose std::is_unsigned implies std::is_integral ? Technically it doesn't, it only checks if it's an arithmetic type. But I haven't see unsigned floats yet. > > Could we match the C++20 requirements to avoid accidental use of this > function that would not work with the C++20 version when we'll switch to > that standard ? I think `is_unsigned` gets us pretty close. Otherwise you'd need to do a series of `std::is_same_v<...>` to match the C++20 requirements. > >>>>> + >>>>> + return x != 0 && (x & (x - 1)) == 0; >>>> >>>> cppreference.com has a more "compact" >>>> >>>> return x && !(x & (x - 1)); >>>> >>>> Up to you! >>>> >>>> Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com> >>>> >>>>> +} >>>>> + >>>>> } /* namespace libcamera::details::cxx20 */ >
diff --git a/include/libcamera/base/details/cxx20.h b/include/libcamera/base/details/cxx20.h index 2d26db53e..8bf45ff11 100644 --- a/include/libcamera/base/details/cxx20.h +++ b/include/libcamera/base/details/cxx20.h @@ -7,9 +7,19 @@ #pragma once +#include <type_traits> + namespace libcamera::details::cxx20 { template<typename T> struct type_identity { using type = T; }; template<typename T> using type_identity_t = typename type_identity<T>::type; +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::details::cxx20 */
`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> --- include/libcamera/base/details/cxx20.h | 10 ++++++++++ 1 file changed, 10 insertions(+)