From 26728848b4c1d3a50ba8986531406e07e7d733cb Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 29 Dec 2020 00:29:44 +0200
Subject: [PATCH] Add bit_ceil

---
 include/boost/core/bit.hpp | 64 +++++++++++++++++++++++++++++++++++--
 test/Jamfile.v2            |  1 +
 test/bit_ceil_test.cpp     | 65 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 127 insertions(+), 3 deletions(-)
 create mode 100644 test/bit_ceil_test.cpp

diff --git a/include/boost/core/bit.hpp b/include/boost/core/bit.hpp
index efbcc50..6258591 100644
--- a/include/boost/core/bit.hpp
+++ b/include/boost/core/bit.hpp
@@ -197,15 +197,73 @@ BOOST_CONSTEXPR T bit_width( T x ) BOOST_NOEXCEPT
     return std::numeric_limits<T>::digits - boost::core::countl_zero( x );
 }
 
-template<class T>
-BOOST_CONSTEXPR T bit_ceil( T x ) BOOST_NOEXCEPT;
-
 template<class T>
 BOOST_CONSTEXPR T bit_floor( T x ) BOOST_NOEXCEPT
 {
     return x == 0? 0: T(1) << ( boost::core::bit_width( x ) - 1 );
 }
 
+namespace detail
+{
+
+BOOST_CXX14_CONSTEXPR inline boost::uint32_t bit_ceil_impl( boost::uint32_t x ) BOOST_NOEXCEPT
+{
+    if( x == 0 )
+    {
+        return 0;
+    }
+
+    --x;
+
+    x |= x >> 1;
+    x |= x >> 2;
+    x |= x >> 4;
+    x |= x >> 8;
+    x |= x >> 16;
+
+    ++x;
+
+    return x;
+}
+
+BOOST_CXX14_CONSTEXPR inline boost::uint64_t bit_ceil_impl( boost::uint64_t x ) BOOST_NOEXCEPT
+{
+    if( x == 0 )
+    {
+        return 0;
+    }
+
+    --x;
+
+    x |= x >> 1;
+    x |= x >> 2;
+    x |= x >> 4;
+    x |= x >> 8;
+    x |= x >> 16;
+    x |= x >> 32;
+
+    ++x;
+
+    return x;
+}
+
+} // namespace detail
+
+template<class T>
+BOOST_CXX14_CONSTEXPR T bit_ceil( T x ) BOOST_NOEXCEPT
+{
+    BOOST_STATIC_ASSERT( sizeof(T) <= sizeof(boost::uint64_t) );
+
+    if( sizeof(T) <= sizeof(boost::uint32_t) )
+    {
+        return static_cast<T>( boost::core::detail::bit_ceil_impl( static_cast<boost::uint32_t>( x ) ) );
+    }
+    else
+    {
+        return static_cast<T>( boost::core::detail::bit_ceil_impl( static_cast<boost::uint64_t>( x ) ) );
+    }
+}
+
 // endian
 
 #if !defined(BOOST_NO_CXX11_SCOPED_ENUMS)
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 76d0386..926e175 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -229,6 +229,7 @@ run bit_countl_test.cpp ;
 run bit_width_test.cpp ;
 run has_single_bit_test.cpp ;
 run bit_floor_test.cpp ;
+run bit_ceil_test.cpp ;
 
 use-project /boost/core/swap : ./swap ;
 build-project ./swap ;
diff --git a/test/bit_ceil_test.cpp b/test/bit_ceil_test.cpp
new file mode 100644
index 0000000..1509d55
--- /dev/null
+++ b/test/bit_ceil_test.cpp
@@ -0,0 +1,65 @@
+// Test for boost/core/bit.hpp (bit_ceil)
+//
+// Copyright 2020 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/core/bit.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/core/detail/splitmix64.hpp>
+#include <boost/cstdint.hpp>
+#include <limits>
+
+template<class T> void test_bit_ceil( T x )
+{
+    if( !boost::core::has_single_bit( x ) )
+    {
+        x >>= 1;
+    }
+
+    T y = boost::core::bit_ceil( x );
+
+    if( x == 0 )
+    {
+        BOOST_TEST_EQ( y, 0 );
+    }
+    else
+    {
+        BOOST_TEST( boost::core::has_single_bit( y ) );
+        BOOST_TEST_GE( +y, +x );
+        BOOST_TEST_LT( y >> 1, +x );
+    }
+}
+
+int main()
+{
+    {
+        test_bit_ceil( static_cast<unsigned char>( 0 ) );
+        test_bit_ceil( static_cast<unsigned short>( 0 ) );
+        test_bit_ceil( static_cast<unsigned int>( 0 ) );
+        test_bit_ceil( static_cast<unsigned long>( 0 ) );
+        test_bit_ceil( static_cast<unsigned long long>( 0 ) );
+    }
+
+    {
+        test_bit_ceil( static_cast<boost::uint8_t>( 0x80 ) );
+        test_bit_ceil( static_cast<boost::uint16_t>( 0x8000 ) );
+        test_bit_ceil( static_cast<boost::uint32_t>( 0x80000000 ) );
+        test_bit_ceil( static_cast<boost::uint64_t>( 0x8000000000000000 ) );
+    }
+
+    boost::detail::splitmix64 rng;
+
+    for( int i = 0; i < 1000; ++i )
+    {
+        boost::uint64_t x = rng();
+
+        test_bit_ceil( static_cast<unsigned char>( x ) );
+        test_bit_ceil( static_cast<unsigned short>( x ) );
+        test_bit_ceil( static_cast<unsigned int>( x ) );
+        test_bit_ceil( static_cast<unsigned long>( x ) );
+        test_bit_ceil( static_cast<unsigned long long>( x ) );
+    }
+
+    return boost::report_errors();
+}