Problem occurring on both Chrome 40.0.2214.93 (64-bit) and Firefox 35.0.1
on OSX 10.8.5.
I wasn't aware of this PRECISE_F32 flag, thanks. But I'm a but confused
here, the documentation says :
ar PRECISE_F32 = 0; // 0: Use JS numbers for floating-point values. These
are 64-bit and do not model C++
// floats exactly, which are 32-bit.
Now if I use the following JS code instead of C in the first place, it
works:
midiToFreq = function (note)
{
return 440.0 * Math.pow(2.0, (note - 69.0) / 12.0);
}
Then using -s PRECISE_F32=1 or -s PRECISE_F32=2 works, and I read
that PRECISE_F32=2 is preferable. So now what is the best option:
1) just use the "double" midiToFreq version in the original C code and
emcripten
2) or use the "float" version in the C original C code, emcripten
and -s PRECISE_F32=2
3) to just avoid the C midiToFreq and use the pure JS midiToFreq version
instead?
Thanks.
Stéphane
Le jeudi 29 janvier 2015 00:30:32 UTC+1, Alon Zakai a écrit :
>
> Which platform and which JS engine is that?
>
> There are several possible issues here. The JS engine might be using the
> system libc pow, but it might have it's own implementation (e.g. sin and
> cos have been implemented in browsers), and different libcs and so forth
> can be more or less precise. Also, since there are floats here, building
> with -s PRECISE_F32=1 can make the results more like native. With that I
> get almost identical results, but still some tiny rounding errors. But even
> without it, the errors are much smaller than yours.
>
> - Alon
>
>
>
> On Wed, Jan 28, 2015 at 1:43 PM, Stéphane Letz <[email protected]
> <javascript:>> wrote:
>
>> The following code :
>>
>>
>> double midiToFreq(double note)
>>
>> {
>>
>> return 440.0 * pow(2.0, (note-69.0)/12.0);
>>
>> }
>>
>>
>> float midiToFreq2(float note)
>>
>> {
>>
>> return 440.0f * powf(2.0f, (note-69.0f)/12.0f);
>>
>> }
>>
>>
>> int main()
>>
>> {
>>
>> for (int i = 48; i < 84; i++) {
>>
>> printf("pitch %d %f\n", i, midiToFreq(i));
>>
>> printf("pitch %d %f\n", i, midiToFreq2(i));
>>
>> }
>>
>> }
>>
>> correctly gives :
>>
>> pitch 48 130.812783
>> pitch 48 130.812775
>> pitch 49 138.591315
>> pitch 49 138.591324
>> pitch 50 146.832384
>> pitch 50 146.832382
>> pitch 51 155.563492
>> pitch 51 155.563492
>> pitch 52 164.813778
>> pitch 52 164.813782
>> pitch 53 174.614116
>> ….
>>
>> when compiled with a C compiler and incorrectly gives the following when
>> compiled with emcc and displayed in JS :
>>
>> pitch 48 130.812783
>> pitch 48 130.812783
>> pitch 49 138.591315
>> pitch 49 136.604359
>> pitch 50 146.832384
>> pitch 50 148.968110
>> pitch 51 155.563492
>> pitch 51 155.563492
>> pitch 52 164.813778
>> pitch 52 162.450876
>> pitch 53 174.614116
>> pitch 53 177.153937
>> pitch 54 184.997211
>>
>> When could be the reason for this strange behavior of the powf function ?
>>
>> Thanks.
>>
>> Stéphane Letz
>>
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