[vlc-devel] [PATCH] core: fix vlc_tick_now on darwin platform

[Steve Lhomme]

Not having a mac like most people I can only make changes blindly and 
hope it works. I did take some time on these changes to make sure I 
didn't overlook something, but it wasn't enough.

On 27/09/2018 06:00, Zhao Zhili wrote:
> I didn't build on MacOS for a few days, so I didn't know from when 
> does the MacOS version was broken. Debugging on this issue really 
> takes some time including slow rebuild on old MacBook. So please do 
> some basic test before push. I can help on the test if you don't have 
> the environment.
>
> On 2018年09月27日 11:42, Zhao Zhili wrote:
>> ---
>>   src/darwin/thread.c | 10 +++-------
>>   1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/src/darwin/thread.c b/src/darwin/thread.c
>> index f5eb4f2..0dd1e3c 100644
>> --- a/src/darwin/thread.c
>> +++ b/src/darwin/thread.c
>> @@ -516,14 +516,10 @@ vlc_tick_t vlc_tick_now (void)
>>       vlc_clock_setup();
>>       uint64_t date = mach_absolute_time();
>>   -    /* denom is uint32_t, switch to 64 bits to prevent overflow. */
>> -    uint64_t denom = vlc_clock_conversion_factor.denom;
>> -
>> -    /* Switch to microsecs */
>> -    denom *= UINT64_C(1000);
>> -
>>       /* Split the division to prevent overflow */
>> -    return vlc_tick_from_frac( date * 
>> vlc_clock_conversion_factor.numer, denom );
>> +    lldiv_t d = lldiv (vlc_clock_conversion_factor.numer, 
>> vlc_clock_conversion_factor.denom);
>> +    date = (d.quot * date) + ((d.rem * date) / 
>> vlc_clock_conversion_factor.denom);

Here the (date * d.rem) might overflow. The original 1000 multiplication 
was lowering the d.rem value which was less bound to overflow.

In practice it really depends on the common values of 
vlc_clock_conversion_factor.numer / vlc_clock_conversion_factor.denom. I 
suspect they are both small values.

>> +    return VLC_TICK_FROM_NS(date);
>>   }
>>     #undef vlc_tick_wait
>
>
>
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