void encrypt(unsigned long k[], unsigned long text[]) {
	unsigned long y = text[0], z = text[1];
	unsigned long delta = 0x9e3779b9, sum = 0; int n;
	for (n= 0; n < 32; n++) {
		sum += delta;
		y += ((z << 4) + k[0]) ^ (z+sum) ^ ((z >> 5) + k[1]);
		z += ((y << 4) + k[2]) ^ (y+sum) ^ ((y >> 5) + k[3]);
	}
	text[0] = y;  text[1] = z; 
}

void decrypt(unsigned long k[], unsigned long text[]) {
	unsigned long y = text[0], z = text[1];
	unsigned long delta = 0x9e3779b9, sum = delta << 5;  int n;
	for (n= 0; n < 32; n++) {
		z -= ((y << 4) + k[2]) ^ (y + sum) ^ ((y >> 5) + k[3]);
		y -= ((z << 4) + k[0]) ^ (z + sum) ^ ((z >> 5) + k[1]);
		sum -= delta;
	}
	text[0] = y; text[1] = z; 
}

void tea(char mode, FILE *infile, FILE *outfile, unsigned long k[]) {
/* mode is 'e' for encrypt, 'd' for decrypt, k[] is the key.*/
	char ch, Text[8]; int i;
	while(!feof(infile)) 
		i = fread(Text, 1, 8, infile);					/* read 8 bytes from infile into Text */
		if (i <= 0) break;
		while (i < 8) { Text[i++] = ' ';}				/* pad last block with spaces */
		switch (mode) {
		case 'e':
			encrypt(k, (unsigned long*) Text); break;
		case 'd':
			decrypt(k, (unsigned long*) Text); break;
		}
		fwrite(Text, 1, 8, outfile);					/* write 8 bytes from Text to outfile */
	}
}