use Benchmark;

$hash1 = { a => '56',
           b => '75',
           c => '87'
         };
         
$hash2 = { d => '45',
           f => '46',
           g => '67',
          };
          

timethese(1000000, { 
            trs80_way => sub { $hash1 = { %$hash1, %$hash2 };  },
            tilly_way => sub { @$hash1{keys %$hash2} = values %$hash2; },
        }
        );