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    date             code       id    cur    hrs     tips
2011-01-21 12:00:00    1    BP1616    USD    10    5
...
2011-01-27 12:00:00    1    PT3232    USD    12    100
2011-01-28 12:00:00    1    PT3232    USD    0    50
2011-01-29 12:00:00    1    PT3232    USD    10    50

#!/usr/bin/perl
...
print "$row->{dat}\t$row->{code}\t$row->{id}\t$row->{cur}\t$row->{hrs}
+\t$row->{tips}\n";

}

  data              code    id      cur      hrs     tips
2011-01-21 12:00:00    1    BP1616    USD    18    20
...
2011-01-27 12:00:00    1    PT3232    USD    12    100
2011-01-28 12:00:00    1    PT3232    USD    0    50
2011-01-29 12:00:00    1    PT3232    USD    10    50

     date            code     id    cur    beg_hr  end_hr beg_tip  end
+_tip
2011-01-21 12:00:00    1    BP1616    USD    0    18    0    20
...
2011-01-23 12:00:00    1    PP3232    USD    108    108    30    30
2011-01-24 12:00:00    1    PP3232    USD    108    112    30    45
2011-01-25 12:00:00    1    PP3232    USD    112    116    45    60

For the first day, 
beg_hr = beg_tip = 0;
...
end_tip(current) = beg_tip(current) + tips(current)

This pattern should continue until last day is reached.