func (fds *FDSet) IsSet(fd uintptr) bool {
	return fds.Bits[fd/NFDBITS]&(1<<(fd%NFDBITS)) != 0
}
IsSet check if the given fd is set
package goselect
import "syscall"
const FD_SETSIZE = syscall.FD_SETSIZE
type FDSet syscall.FdSet
func (fds *FDSet) Set(fd uintptr) {
	fds.Bits[fd/NFDBITS] |= (1 << (fd % NFDBITS))
}
func (fds *FDSet) Clear(fd uintptr) {
	fds.Bits[fd/NFDBITS] &^= (1 << (fd % NFDBITS))
}