The bug is easily fixable. Change: 

sub _daygm {
    $_[3] + ($Cheat{pack("ss",@_[4,5])} ||= do {
    my $month = ($_[4] + 10) % 12;
    my $year = $_[5] + 1900 - $month/10;
    365*$year + $year/4 - $year/100 + $year/400 + ($month*306 + 5)/10 
+- $Epoc
    });
}

[download]

to 

sub _daygm {
    $_[3] + ($Cheat{pack("ss",@_[4,5])} ||= do {
    my $month = ($_[4] + 10) % 12;
    my $year = $_[5] + 1900 + ($_[4] + 10) / 12 - 1;
    365*$year + $year/4 - $year/100 + $year/400 + ($month*306 + 5)/10 
+- $Epoc
    });
}

[download]

My test: 

use integer;

print("month was new new\n");
print("----- --- --- ---\n");

foreach (0..23) {
   my $month = ($_ + 10) % 12;

   printf("%-5d %-3d %-3d %-3d\n",
      $_,
      -$month/10,
      -$month/10 + $_/12,
      ($_+10)/12-1
   );
}

[download]

outputs 

month was new new
----- --- --- ---
0     -1  -1  -1
1     -1  -1  -1
2     0   0   0
3     0   0   0
4     0   0   0
5     0   0   0
6     0   0   0
7     0   0   0
8     0   0   0
9     0   0   0
10    0   0   0
11    0   0   0
12    -1  0   0
13    -1  0   0
14    0   1   1
15    0   1   1
16    0   1   1
17    0   1   1
18    0   1   1
19    0   1   1
20    0   1   1
21    0   1   1
22    0   1   1
23    0   1   1

[download]

I created a ticket.

In reply to Re: timelocal_nocheck: bug or wrongly understood by ikegami
in thread timelocal_nocheck: bug or wrongly understood by borisz

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