Merge 2019-07 LWG Motion 3

P0553R4 Bit operations

Fixes #3007.

Author: zygoloid

source/numerics.tex

@@ -1317,6 +1317,24 @@
     constexpr T floor2(T x) noexcept;
   template<class T>
     constexpr T log2p1(T x) noexcept;
+
+  // \ref{bit.rotate}, rotating
+  template<class T>
+    [[nodiscard]] constexpr T rotl(T x, int s) noexcept;
+  template<class T>
+    [[nodiscard]] constexpr T rotr(T x, int s) noexcept;
+
+  // \ref{bit.count}, counting
+  template<class T>
+    constexpr int countl_zero(T x) noexcept;
+  template<class T>
+    constexpr int countl_one(T x) noexcept;
+  template<class T>
+    constexpr int countr_zero(T x) noexcept;
+  template<class T>
+    constexpr int countr_one(T x) noexcept;
+  template<class T>
+    constexpr int popcount(T x) noexcept;
 }
 \end{codeblock}
 
@@ -1450,6 +1468,154 @@
 unless \tcode{T} is an unsigned integer type\iref{basic.fundamental}.
 \end{itemdescr}
 
+\rSec2[bit.rotate]{Rotating}
+
+In the following descriptions,
+let \tcode{N} denote \tcode{numeric_limits<T>::digits}.
+
+\begin{itemdecl}
+template<class T>
+  [[nodiscard]] constexpr T rotl(T x, int s) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{rotl}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+Let \tcode{r} be \tcode{s \% N}.
+
+\pnum
+\returns
+If \tcode{r} is \tcode{0}, \tcode{x};
+if \tcode{r} is positive, \tcode{(x << r) | (x >> (N - r))};
+if \tcode{r} is negative, \tcode{rotr(x, -r)}.
+\end{itemdescr}
+
+\begin{itemdecl}
+template<class T>
+  [[nodiscard]] constexpr T rotr(T x, int s) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{rotr}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+Let \tcode{r} be \tcode{s \% N}.
+
+\pnum
+\returns
+If \tcode{r} is \tcode{0}, \tcode{x};
+if \tcode{r} is positive, \tcode{(x >> r) | (x << (N - r))};
+if \tcode{r} is negative, \tcode{rotl(x, -r)}.
+\end{itemdescr}
+
+\rSec2[bit.count]{Counting}
+
+In the following descriptions,
+let \tcode{N} denote \tcode{numeric_limits<T>::digits}.
+
+\begin{itemdecl}
+template<class T>
+  constexpr int countl_zero(T x) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{countl_zero}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+\returns
+The number of consecutive \tcode{0} bits in the value of \tcode{x},
+starting from the most significant bit.
+\begin{note}
+Returns \tcode{N} if \tcode{x == 0}.
+\end{note}
+\end{itemdescr}
+
+\begin{itemdecl}
+template<class T>
+  constexpr int countl_one(T x) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{countl_one}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+\returns
+The number of consecutive \tcode{1} bits in the value of \tcode{x},
+starting from the most significant bit.
+\begin{note}
+Returns \tcode{N} if \tcode{x == numeric_limits<T>::max()}.
+\end{note}
+\end{itemdescr}
+
+\begin{itemdecl}
+template<class T>
+  constexpr int countr_zero(T x) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{countr_zero}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+\returns
+The number of consecutive \tcode{0} bits in the value of \tcode{x},
+starting from the least significant bit.
+\begin{note}
+Returns \tcode{N} if \tcode{x == 0}.
+\end{note}
+\end{itemdescr}
+
+\begin{itemdecl}
+template<class T>
+  constexpr int countr_one(T x) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{countr_one}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+\returns
+The number of consecutive \tcode{1} bits in the value of \tcode{x},
+starting from the least significant bit.
+\begin{note}
+Returns \tcode{N} if \tcode{x == numeric_limits<T>::max()}.
+\end{note}
+\end{itemdescr}
+
+\begin{itemdecl}
+template<class T>
+  constexpr int popcount(T x) noexcept;
+\end{itemdecl}
+
+\indexlibrary{\idxcode{popcount}}%
+\begin{itemdescr}
+\pnum
+\constraints
+\tcode{T} is an unsigned integer type\iref{basic.fundamental}.
+
+\pnum
+\returns
+The number of \tcode{1} bits in the value of \tcode{x}.
+\end{itemdescr}
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

source/support.tex

@@ -547,6 +547,8 @@
   \tcode{<bit>} \\ \rowsep
 \defnlibxname{cpp_lib_bind_front}                           & \tcode{201811L} &
   \tcode{<functional>} \\ \rowsep
+\defnlibxname{cpp_lib_bitops}                               & \tcode{201907L} &
+  \tcode{<bit>} \\ \rowsep
 \defnlibxname{cpp_lib_bool_constant}                        & \tcode{201505L} &
   \tcode{<type_traits>} \\ \rowsep
 \defnlibxname{cpp_lib_bounded_array_traits}                 & \tcode{201902L} &