10 Base Logarithm

I try to calculate 10 base logarithm of numbers which is between 0 and 
1023. I want to show 5 digits fractional. Normally Verilog "log10(x)" 
syntax only show the integer version of the result. I multiply by 100000 
to show the fractional parts but it did not work. How can I fix it?



assign y = 'd100000 * $log10(x);