In short, rather than std_logic_unsigned, use numeric_std_unsigned. Numeric_std_unsigned is part of VHDL-2008,
One motivating reason to use numeric_std_unsigned is that it provides a to_integer conversion for std_logic_vector and std_ulogic_vector – the same as for other types within the IEEE package family.
Jim Lewis
In short, rather than std_logic_unsigned, use numeric_std_unsigned. Numeric_std_unsigned is part of VHDL-2008,
One motivating reason to use numeric_std_unsigned is that it provides a to_integer conversion for std_logic_vector and std_ulogic_vector – the same as for other types within the IEEE package family.