// The following code is the fast inverse square root implementation from Quake III Arena
// this code has been stripped of C preprocessor directives, but includes the exact original comment text
float Q_rsqrt( float number )
{
	long i;
	float x2, y;
	const float threehalfs = 1.5F;

	x2 = number * 0.5F;
	y  = number;
	i  = * ( long * ) &y;                       // evil floating point bit level hacking
	i  = 0x5f3759df - ( i >> 1 );               // what the fuck? 
	y  = * ( float * ) &i;
	y  = y * ( threehalfs - ( x2 * y * y ) );   // 1st iteration
//	y  = y * ( threehalfs - ( x2 * y * y ) );   // 2nd iteration, this can be removed

	return y;
}

//Leif Messinger
const int BUZZER_PIN = 8;
const int BUTTON_PIN = 2;
const int BUTTON_PINMODE = INPUT_PULLUP;
#define DEBOUNCE_DELAY 50
class Button{
	private:
	short buttonPin;
	bool buttonState;
	bool lastButtonState;
	int lastDebounceTime;
	public:
	Button(short buttonPin): buttonState(HIGH), lastButtonState(LOW), lastDebounceTime(millis()){
	this->buttonPin = buttonPin;
	}
	bool checkForPress(const bool desiredState){ //Returns true if button pressed
	bool reading = (bool)digitalRead(buttonPin);
	
	// check to see if you just pressed the button
	// (i.e. the input went from LOW to HIGH), and you've waited long enough
	// since the last press to ignore any noise:
	
	// If the switch changed, due to noise or pressing:
	if (reading != lastButtonState) {
	// reset the debouncing timer
	lastDebounceTime = millis();
	}else if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) {
	// whatever the reading is at, it's been there for longer than the debounce
	// delay, so take it as the actual current state:
	
	// if the button state has changed:
	if (reading != buttonState) {
	buttonState = reading;
	
	// only toggle the LED if the new button state is HIGH
	if (buttonState == desiredState) {
	return true;
	}
	}
	}
	
	// save the reading. Next time through the loop, it'll be the lastButtonState:
	lastButtonState = reading;
	return false;
	}
	void waitForPress(const bool desiredState){
	while(!checkForPress(desiredState));
	}
};

class Note{
	public:
	short frequency; //Short max is ~ 30k, so way higher than you can hear
	short lag; //Also 30k ms is 30 seconds
	float sustainPercentage;
};
const short normalBeatLength = 500;
const short wholeNote = 4*normalBeatLength;
const short halfNote = 2*normalBeatLength;
const short dottedQuarterNote = normalBeatLength + (normalBeatLength / 2);
const short quarterNote = normalBeatLength;
const short dottedEighthNote = ((3 * normalBeatLength) / 4);
const short eighthNote = normalBeatLength/ 2;
const short sixteenthNote = normalBeatLength / 4;
const float normalSustainLength = .25;

void beep(const Note& note){ //It might go terribly wrong if you try to beep two tones at the same time.
	tone(BUZZER_PIN, note.frequency);
	delay(note.lag * note.sustainPercentage);
	noTone(BUZZER_PIN);
	delay(note.lag * (1.0 - note.sustainPercentage));
}

Note song[] = {
	{(int)523.25, halfNote, normalSustainLength},
	{(int)392, eighthNote, normalSustainLength},
	{(int)523.25, quarterNote, normalSustainLength},
	{(int)392, dottedEighthNote, normalSustainLength},
	{(int)440.00, sixteenthNote, normalSustainLength},
	{(int)493.88, quarterNote, normalSustainLength},
	{(int)329.63, eighthNote, normalSustainLength},
	{(int)329.63, eighthNote, normalSustainLength},
	{(int)440.00, quarterNote, normalSustainLength},
	{(int)392, dottedEighthNote, normalSustainLength},
	{(int)349.23, sixteenthNote, normalSustainLength},
	{(int)392, quarterNote, normalSustainLength},
	{(int)261.63, dottedEighthNote, normalSustainLength},
	{(int)261.63, sixteenthNote, normalSustainLength},
	{(int)293.66, quarterNote, normalSustainLength},
	{(int)293.66, dottedEighthNote, normalSustainLength},
	{(int)329.63, sixteenthNote, normalSustainLength},
	{(int)349.23, quarterNote, normalSustainLength},
	{(int)349.23, dottedEighthNote, normalSustainLength},
	{(int)392.00, sixteenthNote, normalSustainLength},
	{(int)440.00, quarterNote, normalSustainLength},
	{(int)493.88, eighthNote, normalSustainLength},
	{(int)523.25, eighthNote, normalSustainLength},
	{(int)587.33, dottedQuarterNote, normalSustainLength},
	{(int)392, eighthNote, normalSustainLength},
	{(int)659.25, quarterNote, normalSustainLength},
	{(int)587.33, dottedEighthNote, normalSustainLength},
	{(int)523.25, sixteenthNote, normalSustainLength},
	{(int)587.33, quarterNote, normalSustainLength},
	{(int)493.88, eighthNote, normalSustainLength},
	{(int)392, eighthNote, normalSustainLength},
	{(int)523.25, quarterNote, normalSustainLength},
	{(int)493.88, dottedEighthNote, normalSustainLength},
	{(int)440.00, sixteenthNote, normalSustainLength},
	{(int)493.88, quarterNote, normalSustainLength},
	{(int)329.63, eighthNote, normalSustainLength},
	{(int)329.63, eighthNote, normalSustainLength},
	{(int)440.00, quarterNote, normalSustainLength},
	{(int)392, dottedEighthNote, normalSustainLength},
	{(int)349.23, sixteenthNote, normalSustainLength},
	{(int)392, quarterNote, normalSustainLength},
	{(int)261.63, dottedEighthNote, normalSustainLength},
	{(int)261.63, sixteenthNote, normalSustainLength},
	{(int)523.25, quarterNote, normalSustainLength},
	{(int)493.88, dottedEighthNote, normalSustainLength},
	{(int)440.00, sixteenthNote, normalSustainLength},
	{(int)392.00, halfNote, normalSustainLength * .5},
};
size_t songLength = (sizeof(song) / sizeof(Note));

void playSong(){
	for(size_t pos = 0; pos < songLength; ++pos){
	const Note& bruh = song[pos];
	beep(bruh);
	}
}

void setup() {
	const int BUZZER_PIN = 8;
	pinMode(BUZZER_PIN, OUTPUT);
	pinMode(BUTTON_PIN, BUTTON_PINMODE);
	playSong();
}

Button button(BUTTON_PIN);
void loop() {
	button.waitForPress(LOW);
	// read the state of the switch into a local variable:
	playSong();
}

#include <stdio.h>
#include <unistd.h>

int main() {
  char * cmd[] = {
    "who",
    "ls",
    "date"
  };
  int i;
  printf("0=who 1=ls 2=date : ");
  scanf("%d", & i);
  execlp(cmd[i], cmd[i], (char * ) 0);
  printf("execlp failed\n");
  return 0;
}

#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define READ 0 /* The index of the read end of the pipe */
#define WRITE 1 /* The index of the write end of the pipe */
char * phrase = "This goes in the pipe";
int main() {
  int fd[2], bytesRead;
  char message[100]; /* Parent process' message buffer */
  pipe(fd); /* Create unnamed pipe */
  if (fork() == 0) /* Child, writer */ {
    close(fd[READ]); /* Close unused end */
    write(fd[WRITE], phrase, strlen(phrase) + 1); /* Include NULL */
    close(fd[WRITE]); /* Close used end */
  } else /* Parent, reader */ {
    close(fd[WRITE]); /* Close unused end */
    bytesRead = read(fd[READ], message, 100);
    printf("Parent just read %i bytes: %s\n", bytesRead, message);
    close(fd[READ]); /* Close used end */
  }
}

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>

int glbvar = 6;
int main() {
  int locvar = 88;
  pid_t pid;
  printf("Before fork()\n");
  if ((pid = fork()) == 0) {
    /* child */
    glbvar++;
    locvar++;
  } else if (pid > 0) {
    /* parent */
    sleep(2);
  } else
    perror("fork error");
  printf("pid=%d, glbvar=%d, locvar=%d\n", getpid(), glbvar, locvar);
  return 0;
} /* end main */

// Server side implementation of UDP client-server model
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT     8008
#define MAXLINE 1024

// Driver code
int main(){
        int sockfd;
        char buffer[MAXLINE];
        char *hello = "Hello from server";
        struct sockaddr_in servaddr, cliaddr;

        // Creating socket file descriptor
        if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
                perror("socket creation failed");
                exit(EXIT_FAILURE);
        }

        memset(&servaddr, 0, sizeof(servaddr));
        memset(&cliaddr, 0, sizeof(cliaddr));

        // Filling server information
        servaddr.sin_family    = AF_INET; // IPv4
        servaddr.sin_addr.s_addr = INADDR_ANY;
        servaddr.sin_port = htons(PORT);

        // Bind the socket with the server address
        if ( bind(sockfd, (const struct sockaddr *)&servaddr, sizeof(servaddr)) < 0 ){
                perror("bind failed");
                exit(EXIT_FAILURE);
        }

        int len, n;

        len = sizeof(cliaddr);  //len is value/result

        n = recvfrom(sockfd, (char *)buffer, MAXLINE, MSG_WAITALL, ( struct sockaddr *) &cliaddr, &len);
        buffer[n] = '\0';
        printf("Client : %s\n", buffer);
        sendto(sockfd, (const char *)hello, strlen(hello), MSG_CONFIRM, (const struct sockaddr *) &cliaddr, len);
        printf("Hello message sent.\n");

        return 0;
}