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Bug 1925 - SDL_GetPerformanceFrequency - returns 0
Summary: SDL_GetPerformanceFrequency - returns 0
Status: RESOLVED FIXED
Alias: None
Product: SDL
Classification: Unclassified
Component: timer (show other bugs)
Version: don't know
Hardware: iPhone/iPod touch iOS (All)
: P2 normal
Assignee: Sam Lantinga
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2013-06-21 09:00 UTC by PoopiSan
Modified: 2013-08-10 15:17 UTC (History)
1 user (show)

See Also:

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Description PoopiSan 2013-06-21 09:00:13 UTC 
SDL_GetPerformanceFrequency is incorrectly implemented on Apple machines.

Currently on OSX and iOS simulator the values:
mach_base_info.denom = 1
mach_base_info.numer = 1

but on the real iOS device
mach_base_info.denom = 3
mach_base_info.numer = 125

The calculation is made using following formula
mach_base_info.denom / mach_base_info.numer * 1000000

but all values are int32 and the result is casted to int64.

This solves the problem:

return 1.0 * mach_base_info.denom / mach_base_info.numer * 1000000;
Comment 1 Sam Lantinga 2013-06-24 01:23:23 UTC 
Thanks for the report!
This should be fixed:
http://hg.libsdl.org/SDL/rev/c3052ed2c310
Comment 2 sofmz 2013-08-10 01:43:43 UTC 
it doesn't seem to be fixed yet. I've downloaded the latest snapshot(SDL-2.0.0-7602), it doesn't return 0 anymore but a weird number.


I've fixed it by changing it to : 

#elif defined(__APPLE__)
        return (mach_base_info.denom * 1000000) / mach_base_info.numer;
#endif


from 


#elif defined(__APPLE__)
        Uint64 freq = mach_base_info.numer;
        freq *= 1000000000;
        freq /= mach_base_info.denom;
        return freq;
#endif
Comment 3 Sam Lantinga 2013-08-10 02:10:10 UTC 
It works for me here.

What's the output of this code for you?
    Uint32 start32, now32;
    Uint64 start, now;

    printf("Performance counter frequency: %llu\n", (unsigned long long) SDL_GetPerformanceFrequency());
    start32 = SDL_GetTicks();
    start = SDL_GetPerformanceCounter();
    SDL_Delay(1000);
    now = SDL_GetPerformanceCounter();
    now32 = SDL_GetTicks();
    printf("Delay 1 second = %d ms in ticks, %f ms according to performance counter\n", (now32-start32), (double)((now - start)*1000) / SDL_GetPerformanceFrequency());
Comment 4 sofmz 2013-08-10 03:08:47 UTC 
(In reply to comment #3)
> It works for me here.
> 
> What's the output of this code for you?
>     Uint32 start32, now32;
>     Uint64 start, now;
> 
>     printf("Performance counter frequency: %llu\n", (unsigned long long)
> SDL_GetPerformanceFrequency());
>     start32 = SDL_GetTicks();
>     start = SDL_GetPerformanceCounter();
>     SDL_Delay(1000);
>     now = SDL_GetPerformanceCounter();
>     now32 = SDL_GetTicks();
>     printf("Delay 1 second = %d ms in ticks, %f ms according to performance
> counter\n", (now32-start32), (double)((now - start)*1000) /
> SDL_GetPerformanceFrequency());


The SDL_GetPerformanceFrequency code in snapshot SDL-2.0.0-7602 works correctly on simulator only but not on real iOS devices.

Btw, this is the output I've tested on my iPad : 

Delay 1 second = 1025 ms in ticks, 0.590138 ms according to performance counter
Performance counter frequency: 41666666666
Comment 5 Sam Lantinga 2013-08-10 14:20:02 UTC 
Fixed, thanks for checking this! :)
http://hg.libsdl.org/SDL/rev/ebf5f6859e40
Comment 6 sofmz 2013-08-10 15:17:21 UTC 
No problem! I'm glad it helps. :)