From 26991f0c756bfde745bbd2156545065423515673 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Mon, 28 Dec 2020 23:52:39 +0200
Subject: [PATCH] Add bit_width_test

---
 test/Jamfile.v2         |  1 +
 test/bit_width_test.cpp | 94 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 test/bit_width_test.cpp

diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index 62942c4..a624eee 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -226,6 +226,7 @@ run bit_cast_test.cpp ;
 run bit_rotate_test.cpp ;
 run bit_countr_test.cpp ;
 run bit_countl_test.cpp ;
+run bit_width_test.cpp ;
 
 use-project /boost/core/swap : ./swap ;
 build-project ./swap ;
diff --git a/test/bit_width_test.cpp b/test/bit_width_test.cpp
new file mode 100644
index 0000000..1447b90
--- /dev/null
+++ b/test/bit_width_test.cpp
@@ -0,0 +1,94 @@
+// Test for boost/core/bit.hpp (bit_width)
+//
+// 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_width( T x )
+{
+    BOOST_TEST_EQ( boost::core::bit_width( x ), std::numeric_limits<T>::digits - boost::core::countl_zero( x ) );
+}
+
+int main()
+{
+    {
+        boost::uint8_t x = 0;
+
+        BOOST_TEST_EQ( boost::core::bit_width( x ), 0 );
+
+        x = 1;
+
+        for( int i = 0; i < 8; ++i, x <<= 1 )
+        {
+            BOOST_TEST_EQ( boost::core::bit_width( x ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint8_t>( x | ( x >> 1 ) ) ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint8_t>( x | ( x >> 2 ) ) ), i+1 );
+        }
+    }
+
+    {
+        boost::uint16_t x = 0;
+
+        BOOST_TEST_EQ( boost::core::bit_width( x ), 0 );
+
+        x = 1;
+
+        for( int i = 0; i < 16; ++i, x <<= 1 )
+        {
+            BOOST_TEST_EQ( boost::core::bit_width( x ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint16_t>( x | ( x >> 1 ) ) ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint16_t>( x | ( x >> 2 ) ) ), i+1 );
+        }
+    }
+
+    {
+        boost::uint32_t x = 0;
+
+        BOOST_TEST_EQ( boost::core::bit_width( x ), 0 );
+
+        x = 1;
+
+        for( int i = 0; i < 32; ++i, x <<= 1 )
+        {
+            BOOST_TEST_EQ( boost::core::bit_width( x ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint32_t>( x | ( x >> 1 ) ) ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint32_t>( x | ( x >> 2 ) ) ), i+1 );
+        }
+    }
+
+    {
+        boost::uint64_t x = 0;
+
+        BOOST_TEST_EQ( boost::core::bit_width( x ), 0 );
+
+        x = 1;
+
+        for( int i = 0; i < 64; ++i, x <<= 1 )
+        {
+            BOOST_TEST_EQ( boost::core::bit_width( x ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint64_t>( x | ( x >> 1 ) ) ), i+1 );
+            BOOST_TEST_EQ( boost::core::bit_width( static_cast<boost::uint64_t>( x | ( x >> 2 ) ) ), i+1 );
+        }
+    }
+
+    boost::detail::splitmix64 rng;
+
+    for( int i = 0; i < 1000; ++i )
+    {
+        boost::uint64_t x = rng();
+
+        test_width( static_cast<unsigned char>( x ) );
+        test_width( static_cast<unsigned short>( x ) );
+        test_width( static_cast<unsigned int>( x ) );
+        test_width( static_cast<unsigned long>( x ) );
+        test_width( static_cast<unsigned long long>( x ) );
+    }
+
+    return boost::report_errors();
+}