simple and effective way to store date / time in only 4 byte

date_time_compact.c

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

short date_compress(int day, int month, int year) {
    short d = ((((year % 100) << 4) + month) << 5) + day;
    return d;
}

int* date_decompress(int cdate) {
    static int d[3];
    
    d[0] = cdate & 0x1f;
    d[1] = (cdate >> 5) & 0xf;
    d[2] = 2000 + (cdate >> (5 + 4));
    
    return d;
}

short time_compress(int hour, int minute, int second) {
    short t = (((second << 6) + minute) << 4) + hour;
    return t;
}

int* time_decompress(int ct) {
    static int t[3];
    
    t[0] = ct & 0xf;
    t[1] = (ct >> 4) & 0x3f;
    t[2] = (ct >> 10) & 0x3f;
    
    return t;
}

int date_time_compress(int day, int month, int year, int hour, int minute, int second) {
    int dt = (date_compress(day, month, year) << 16) + time_compress(hour, minute, second);
    return dt;
}

int* date_time_decompress(int dtc) {
    int* dt = malloc(8 * sizeof(int));
    
    memcpy(dt, date_decompress(dtc >> 16), 4 * sizeof(int));
    memcpy(dt + 3, time_decompress(dtc), 4 * sizeof(int));
    
    return dt;
}

int main()
{
    int day = 21;
    int month = 3;
    int year = 2019;
    
    int hour = 10;
    int minute = 27;
    int second = 24;
    
    printf("Eingabedaten\n");
    printf("Datum: %i/%i/%i\n", day, month, year);
    printf("Uhrzeit: %i/%i/%i\n\n", hour, minute, second);
    
    short date_compressed = date_compress(day, month, year);
    printf("Datum Komprimiert:");
    printf("%#06x\n", date_compressed);
    
    int *date_decompressed = date_decompress(date_compressed);
    printf("Datum Dekomprimiert:");
    printf("%i/%i/%i\n\n", 
				*date_decompressed, 		// day
				*(date_decompressed + 1), 	// month
				*(date_decompressed + 2));	// year
    
    short time_compressed = time_compress(hour, minute, second);
    printf("Uhrzeit Komprimiert:");
    printf("%#06x\n", time_compressed);
    
    int *time_decompressed = time_decompress(time_compressed);
    printf("Uhrzeit Dekomprimiert:");
    printf("%i/%i/%i\n\n", 
				*time_decompressed, 		// hour
				*(time_decompressed + 1), 	// minute
				*(time_decompressed + 2));	// second
    
    int date_time_compressed = date_time_compress(day, month, year, hour, minute, second);
    printf("Datum/Uhrzeit Komprimiert:");
    printf("%#06x\n", date_time_compressed);
    
    int *date_time_decompressed = date_time_decompress(date_time_compressed);
    printf("Datum/Uhrzeit Dekomprimiert:");
    printf("%i/%i/%i %i/%i/%i\n\n", 
				*date_time_decompressed, 		// day
				*(date_time_decompressed + 1), 	// month
				*(date_time_decompressed + 2), 	// year
				*(date_time_decompressed + 3), 	// hour
				*(date_time_decompressed + 4), 	// minute
				*(date_time_decompressed + 5));	// second

    return 0;
}

date_time_compact.php

<?php

function date_compress($day, $month, $year) {
    $d = (((($year % 100) << 4) + $month) << 5) + $day;
    return $d;
}

function date_decompress($cdate) {
    $d = array();
    
    array_push($d, $cdate & 0x1f);
    array_push($d, ($cdate >> 5) & 0xf);
	array_push($d, 2000 + ($cdate >> (5 + 4)));
    
    return $d;
}

function time_compress($hour, $minute, $second) {
    $t = ((($second << 6) + $minute) << 4) + $hour;
    return $t;
}

function time_decompress($ct) {
    $t = array();
    
	array_push($t, $ct & 0xf);
	array_push($t, ($ct >> 4) & 0x3f);
	array_push($t, ($ct >> 10) & 0x3f);
    
    return $t;
}

function date_time_compress($day, $month, $year, $hour, $minute, $second) {
    $dt = (date_compress($day, $month, $year) << 16) + time_compress($hour, $minute, $second);
    return $dt;
}

function date_time_decompress($dtc) {
    $dt = array_merge(date_decompress($dtc >> 16), time_decompress($dtc));
    return $dt;
}


$day = 21;
$month = 3;
$year = 2019;
    
$hour = 10;
$minute = 27;
$second = 24;
    
printf("Eingabedaten\n");
printf("Datum: %d/%d/%d\n", $day, $month, $year);
printf("Uhrzeit: %d/%d/%d\n\n", $hour, $minute, $second);

$date_compressed = date_compress($day, $month, $year);
printf("Datum Komprimiert:");
printf("0x" . dechex($date_compressed) . "\n");
    
$date_decompressed = date_decompress($date_compressed);
printf("Datum Dekomprimiert:");
printf("%d/%d/%d\n\n", 
				$date_decompressed[0], 	// day
				$date_decompressed[1], 	// month
				$date_decompressed[2]);	// year
				
$time_compressed = time_compress($hour, $minute, $second);
printf("Uhrzeit Komprimiert:");
printf("0x" . dechex($time_compressed) . "\n");
    
$time_decompressed = time_decompress($time_compressed);
printf("Uhrzeit Dekomprimiert:");
printf("%d/%d/%d\n\n", 
				$time_decompressed[0], 		// hour
				$time_decompressed[1], 	// minute
				$time_decompressed[2]);	// second
				
$date_time_compressed = date_time_compress($day, $month, $year, $hour, $minute, $second);
printf("Datum/Uhrzeit Komprimiert:");
printf("0x" . dechex($date_time_compressed) . "\n");
    
$date_time_decompressed = date_time_decompress($date_time_compressed);
printf("Datum/Uhrzeit Dekomprimiert:");
printf("%d/%d/%d %d/%d/%d\n\n", 
				$date_time_decompressed[0], 	// day
				$date_time_decompressed[1], 	// month
				$date_time_decompressed[2], 	// year
				$date_time_decompressed[3], 	// hour
				$date_time_decompressed[4], 	// minute
				$date_time_decompressed[5]);	// second