Add hash_string_test4.cpp

test/Jamfile.v2

@@ -85,3 +85,4 @@ run hash_container_test.cpp ;
 run hash_vector_test2.cpp ;
 
 run hash_string_test3.cpp ;
+run hash_string_test4.cpp ;

test/hash_string_test4.cpp

@@ -0,0 +1,41 @@
+// Copyright 2021, 2022 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/container_hash/hash.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <string>
+#include <cstddef>
+
+void test( std::size_t n, unsigned char ch )
+{
+    typedef boost::hash<std::string> hash;
+
+    std::string const v( n, static_cast<char>( ch ) );
+
+    for( std::size_t i = 0; i < n * 8; ++i )
+    {
+        std::string w( v );
+
+        unsigned char ch2 = static_cast<unsigned char>( w[ i / 8 ] );
+
+        ch2 = static_cast<unsigned char>( ch2 ^ ( 1 << ( i % 8 ) ) );
+
+        w[ i / 8 ] = static_cast<char>( ch2 );
+
+        BOOST_TEST_NE( hash()( v ), hash()( w ) );
+    }
+}
+
+int main()
+{
+    for( unsigned ch = 0; ch < 256; ++ch )
+    {
+        for( std::size_t n = 1; n < 32; ++n )
+        {
+            test( n, static_cast<unsigned char>( ch ) );
+        }
+    }
+
+    return boost::report_errors();
+}