[fpc-pascal] Very vague gettickcount64 description?

[Yuriy Sydorov]

On 08.09.2019 10:09, Michael Van Canneyt wrote:
> 
> 
> On Sat, 7 Sep 2019, Zoe Peterson wrote:
> 
>>> From: Martin Frb <lazarus at mfriebe.de>
>>> But that does not mean, it needs to be changed on existing targets.
>>> And if it is not going to be changed, then it can be documented.
>>
>> I agree with everything Martin has said, though IMO GetTickCount must return values in ms on every single platform and 
>> any that can't should have it removed. It's not a precision timer and it should not be an intrinsic for whatever 
>> random RDTSC-like instruction the current platform has. It's used for checking (rough) elapsed times. I honestly can't 
>> think of a single use for the current function as defined, especially in a cross-platform app. Precision and accuracy 
>> can vary, but unspecified units with no way to query them is ridiculous.
> 
> For relative measurements, units are not needed. A ratio has no units, the
> only thing that is required is that the units for both measurements are the
> same (which should be the case on a single platform).

Strictly defined measurement units are important for cross-platform (and Delphi) compatibility. So GetTickCount_2 - 
GetTickCount_1 must return how many milliseconds have elapsed between calls of GetTickCount regardless of the platform 
where the program is running.

> But I have re-checked the Microsoft documentation, the implementation, and
> have added millisecond units to documentation of gettickcount(64).

Thanks.

> Note that the FPC implementation gives an increasing time, not the number of
> milliseconds elapsed since system boot. Which is what, strictly speaking,
> it should return to comply to the Microsoft implementation.

Yes. Implementing this for every platform would be overkill. GetTickCount in FPC should be documented just as a 
millisecond counter without defined starting point and without guaranteed precision.

Yuriy.