It's C code is given in the link itself.
let kFilteringFactor = 0.1
var kAccelerationX = 0.0
if (arr_motionSensor.count == 0) || flagRestartFilter{
kAccelerationX = motionSensor.acceleration
}
else{
// Applying Low pass kalman Filter of low frequency applied on acceleration
kAccelerationX = (motionSensor.acceleration * kFilteringFactor) + (kAccelerationX * (1.0 - kFilteringFactor))
}