[Gambas-user] Difference DateDiff(...) ?

[d4t4full at ...626...]

Toni,

I don't think Print is at fault here at all. My guess is that DateDiff may need an "attitude adjustment" in these cases: It may need to either raise an overflow error or return a 64bit Long.

Hope this helps,
zxMarce.



On Aug 6, 2017, 12:00, at 12:00, Tony Morehen <tmorehen at ...3602...> wrote:
>zxMarce, you are exactly right.  DateDiff returns an integer so when
>print adds the two datediff it adds 2 signed integers and gets an
>signed
>integer.  Since the max value of a signed integer is 2147483647, the
>answer of 2208988800 overflows to -2085978496. So print's behaviour is
>as expected.  The only question is: Should print raise an overflow
>error?  Note that there has not been a hardware overflow so the
>gambas's
>math engine must do the overflow check (by matching signs).
>
>
>On 2017-08-06 10:30 AM, d4t4full at ...626... wrote:
>> Without a machine nearby, I'd risk you're in the right track.
>>
>> The DIM AS LONG creates 64bit vars while DateDiff may return 32bit
>data (don't have the docs with me).
>>
>> Print will use 64bit to print the vars and 32bit with direct DateDiff
>(you may confirm by using CLng to affect the DateDiff's in the second
>Print)
>>
>> Remember that when you have the most significant bit (MSB) set,
>Gambas will interpret the value as twos-complement sign and yield
>negative values.
>>
>> Regards,
>> zxMarce.
>>
>>
>> On Aug 6, 2017, 10:21, at 10:21, Hans Lehmann <hans at ...3219...>
>wrote:
>>> Hello,
>>> Why are two different results:
>>>
>>> Public Sub Main()
>>>
>>>    Dim a, b As Long
>>>
>>>    a = DateDiff("01/01/1900", "01/01/1935", gb.Second)
>>>    b = DateDiff("01/01/1935", "01/01/1970 ", gb.Second)
>>>
>>>    Print a + b
>>>    Print DateDiff("01/01/1900", "01/01/1935", gb.Second) +
>>> DateDiff("01/01/1935", "01/01/1970 ", gb.Second)
>>>
>>> End
>>>
>>> Results:
>>>
>>> 2208988800     ' ok
>>> -2085978496    ' complement?
>>>
>>> Best regards
>>>
>>> Hans
>>>
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