Need to read a double value from a binary file

Hi all! I need to read 8 bytes from a binary file (shp file) and cast it to its double value... I'm having problems because PHP casts it automaticlly to a string using fread; I can't find the function to cast it correctly, because floatval only removes the non-numeric parts of the variable, but it doesn't cast it completly... I already did a little program in C++ and it casts it perfectly, but I can' find the way to do it in php! Any help will be appreciated!