sub add_hash_slice{
  my $slice = shift or return undef;
  my $hash1 = shift or return undef;
  my $hash2 = shift or return $hash1;
  
  $hash1->{$key} += $hash2->{$key} for my $key( @$slice );

  return $hash1;
} 

#call
add_hash_slice( \@fields, \%totals, \%delta);