Calculates the number of days from January 01, 2000 to a specified day

This is a function that calculates the number of days from January 01, 2000 to a specified day
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(Calculate head also count tail) date format is: YYYY-MM-DD
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<?php
Calculate the number of days from January 01, 2000 to one day

function Cal_start2end ($end _day, $start _day)
{


$start _day=ereg_replace ("-", "", $start _day);
$end _day=ereg_replace ("-", "", $end _day);


if ($end _day>= $start _day)
{//Due date is greater than start date
if (substr ($end _day,0,4) ==substr ($start _day,0,4))
{

if (Is_int (substr ($end _day,0,4)/4))
$leap _day=29; Leap year
Else
$leap _day=28;


Same year

if (substr ($end _day,4,2) ==substr ($start _day,4,2))
{
The same month
$endday _from_startday= $end _day-$start _day 1;

}
Else
{
Not same month


Switch (substr ($end _day,4,2))
{
Case "01":
$endday _from_newyear=substr ($end _day,6,2) 1;
Break
Case "02":
$endday _from_newyear=substr ($end _day,6,2) 31;
Break
Case "03":
$endday _from_newyear=substr ($end _day,6,2) $leap _day 31;
Break
Case "04":
$endday _from_newyear=substr ($end _day,6,2) 1 $leap _day 31*2;
Break
Case "05":
$endday _from_newyear=substr ($end _day,6,2) 1 $leap _day 31*2 30;
Break
Case "06":
$endday _from_newyear=substr ($end _day,6,2) 1 $leap _day 31*3 30;
Break
Case "07":
$endday _from_newyear=substr ($end _day,6,2) 1 $leap _day 31*2 30*2;