High pass and low pass filters in c specifically for the Arduino

hpfilter.c

// Freq is not the frequency in hertz but the time constant RC
int lowpass(int portinput, int freq, int samplerate, int prev){
	int RC = samplerate/(samplerate+freq);
	int returnd = RC*portinput+(1-RC)*prev; 
	return returnd;
}
int highpass(int portinput, int freq, int samplerate, int prevport, int prevproc){
	int RC = samplerate/(samplerate+freq);
	int returnd = RC*(prevproc+portinput-prevproc);
	return returnd;
}