From f08204e29aa3e17567b084a411c465c2d861b236 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Sun, 29 May 2022 21:58:19 +0300
Subject: [PATCH] Revert hash_value for std::complex

---
 include/boost/container_hash/hash.hpp | 13 ++++++-------
 test/hash_complex_test.cpp            | 18 ++++++++----------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/include/boost/container_hash/hash.hpp b/include/boost/container_hash/hash.hpp
index 8fd7cae..7cb2d01 100644
--- a/include/boost/container_hash/hash.hpp
+++ b/include/boost/container_hash/hash.hpp
@@ -86,8 +86,8 @@ namespace boost
         {
             static std::size_t fn( T v )
             {
-				// The bias makes negative numbers that fit into a ssize_t hash to themselves
-				// E.g. hash_value( -4LL ) == (size_t)-4
+                // The bias makes negative numbers that fit into a ssize_t hash to themselves
+                // E.g. hash_value( -4LL ) == (size_t)-4
 
                 std::size_t const bias = (std::numeric_limits<std::size_t>::max)() / 4;
 
@@ -252,12 +252,11 @@ namespace boost
     template <class T>
     std::size_t hash_value( std::complex<T> const& v )
     {
-        std::size_t seed = 0;
+        std::size_t re = boost::hash<T>()( v.real() );
+        std::size_t im = boost::hash<T>()( v.imag() );
 
-        boost::hash_combine( seed, v.real() );
-        boost::hash_combine( seed, v.imag() );
-
-        return seed;
+        im ^= re + ( im << 6 ) + ( im >> 2 );
+        return im;
     }
 
     // pair
diff --git a/test/hash_complex_test.cpp b/test/hash_complex_test.cpp
index 2dbad10..2435ab4 100644
--- a/test/hash_complex_test.cpp
+++ b/test/hash_complex_test.cpp
@@ -53,11 +53,11 @@ void generic_complex_tests(std::complex<T> v)
 
     BOOST_HASH_TEST_NAMESPACE::hash<T> real_hasher;
     T real = v.real();
-    // T imag = v.imag();
+    T imag = v.imag();
 
-    // BOOST_TEST(real_hasher(real) == complex_hasher(std::complex<T>(real)));
+    BOOST_TEST(real_hasher(real) == complex_hasher(std::complex<T>(real)));
 
-    if(real_hasher(real) == complex_hasher(v)) {
+    if(imag != 0 && real_hasher(real) == complex_hasher(v)) {
         std::ostringstream os;
         os<<"real_hasher("<<real<<") == complex_hasher("
             <<v.real()<<" + "<<v.imag()<<"i) == "
@@ -89,10 +89,8 @@ void complex_integral_tests(Integer*)
     generic_complex_tests(complex(Integer(-543),Integer(763)));
 }
 
-template<class T> void complex_grid_test()
+template<class T> void complex_grid_test( short N )
 {
-    short const N = 16;
-
     std::set<std::size_t> hashes;
 
     for( short i = 0; i < N; ++i )
@@ -122,10 +120,10 @@ int main()
     complex_integral_tests((unsigned int*) 0);
     complex_integral_tests((unsigned long*) 0);
 
-    complex_grid_test<int>();
-    complex_grid_test<float>();
-    complex_grid_test<double>();
-    complex_grid_test<long double>();
+    complex_grid_test<int>( 16 );
+    complex_grid_test<float>( 7 );
+    complex_grid_test<double>( 16 );
+    complex_grid_test<long double>( 16 );
 
     return boost::report_errors();
 }