12  while ($dow != $target_dow) {   # do the following until $dow 
+is what we want
    13    # Back up one day
    14    $start -= $seconds_per_day;   # remove a days worth of secon
+ds from our epoch time
    15    if (--$dow < 0) {             # remove one from our $dow cou
+nter  
    16      $dow += 7;                  # if we ended up with -1 as da
+y of week, wrap it back to 6 (-1 + 7)
    17    }                             # end if
    18  }                               # end while loop, now our $dow
+ matches our target
[download]

Cheers,
R.