I think you don't have to do much....
just read the value from the first table and write it to the other
I suppose the only problem would arise if the your numbers are either bigger than 8,388,607 or smaller than -8,388,608.... while copying/pasting you should make this check and raise exception errors (or any other error notifications) for values out of this range
apart from that I think php and the db will handle all the rest smoothly....
but I am not 100% sure of course... maybe you should first make a sample copy, test if everything goes well and continue with the rest of the copy