Synthesize problem

1

for i in n downto 0 loop

2

    if (temp1>=temp2 * 2**i) then

power of two from a non-constant is not synthesizable,

Best to:
* throw away your code
* read working VHD -code i.e. 
http://www.arithmetic-circuits.org/guide2fpga/vhdl_codes.htm
*synthesize that and check reports and rtl/structutal view
*draw block schematic of your implementation
*rewrite synthesizable code from the scratch

Best regards,