On Sat, 24 Nov 2018 14:19:01 +0100
Fons Adriaensen wrote:
>On Sat, Nov 24, 2018 at 10:49:46AM +, Will Godfrey wrote:
>
>> >The safe way is of course:
>> >
>> >int i = (int) floorf (p);
>> >float f = p - i;
>
>> I'd been mulling over *exactly* that point for some time. My reasoning being
On Sat, Nov 24, 2018 at 10:49:46AM +, Will Godfrey wrote:
> >The safe way is of course:
> >
> >int i = (int) floorf (p);
> >float f = p - i;
> I'd been mulling over *exactly* that point for some time. My reasoning being
> that in the latter case, if the integer was slightly wrong then using
On Sat, 24 Nov 2018 11:14:06 +0100
Fons Adriaensen wrote:
>The dangerous thing to do is:
>
>// given float p
>
>int i = (int) floorf (p);
>float f = fmodf (p, 1.0f);
>
>as you could end up with i + f != p.
>
>The safe way is of course:
>
>int i = (int) floorf (p);
>float f = p - i;
>
>
>Ciao,
>
On Thu, Nov 22, 2018 at 11:29:11PM +0100, Robin Gareus wrote:
> A simpler example to show this is
>
> #include
> #include
> int main (int argc, char** argv) {
> float a = 0;
> for (int i = 0; i < 100; ++i) {
> a += 0.1f;
> a -= 0.05f;
> a = fmodf (a, 1.f);
> }
> printf
Am 22.11.18 um 22:41 schrieb Fons Adriaensen:
On Thu, Nov 22, 2018 at 09:27:58PM +0100, Hermann Meyer wrote:
In guitarix nearly all DSP is generated by FAUST.
That doesn't make any difference for numerical stability.
This is a property of an algorithm, not of the language.
Ciao,
Just as
On 11/23/2018 09:18 AM, Gordonjcp wrote:
On Fri, Nov 23, 2018 at 02:09:02PM +0100, Robin Gareus wrote:
On 11/23/2018 01:00 PM, Will Godfrey wrote:
[...]
Thanks for going into this in such detail Robin. I never realised fp stuff
could be *quite* so, umm, approximate!
Depending on context
In Fri, 23 Nov 2018 17:56:38 +
Gordonjcp wrote:
> On Fri, Nov 23, 2018 at 10:33:24PM +0500, Nikita Zlobin wrote:
> > In Fri, 23 Nov 2018 14:18:01 +
> > Gordonjcp wrote:
> >
> > > On Fri, Nov 23, 2018 at 02:09:02PM +0100, Robin Gareus wrote:
> > > > On 11/23/2018 01:00 PM, Will
On Fri, Nov 23, 2018 at 10:33:24PM +0500, Nikita Zlobin wrote:
> In Fri, 23 Nov 2018 14:18:01 +
> Gordonjcp wrote:
>
> > On Fri, Nov 23, 2018 at 02:09:02PM +0100, Robin Gareus wrote:
> > > On 11/23/2018 01:00 PM, Will Godfrey wrote:
> > > [...]
> > > > Thanks for going into this in such
It's probably gonna be silly question, but after short analysis i don't
see, what could be broken in this demo snippet, when float is standard
single-precision 32bit type.
I omit first case, as optimizing compiler could just optimize it to
just =1; though it could do it in second case too... (as
In Fri, 23 Nov 2018 14:18:01 +
Gordonjcp wrote:
> On Fri, Nov 23, 2018 at 02:09:02PM +0100, Robin Gareus wrote:
> > On 11/23/2018 01:00 PM, Will Godfrey wrote:
> > [...]
> > > Thanks for going into this in such detail Robin. I never realised
> > > fp stuff could be *quite* so, umm,
It could be lame question, but still... is it possible, that some
implementations (compiler/hardware) will print 1? (even 64bit doesn't
hold 20 decimal digits).?
In Fri, 23 Nov 2018 14:09:02 +0100
Robin Gareus wrote:
> On 11/23/2018 01:00 PM, Will Godfrey wrote:
> [...]
> > Thanks for going
On Fri, Nov 23, 2018 at 02:09:02PM +0100, Robin Gareus wrote:
> On 11/23/2018 01:00 PM, Will Godfrey wrote:
> [...]
> > Thanks for going into this in such detail Robin. I never realised fp stuff
> > could be *quite* so, umm, approximate!
>
> Depending on context and the maths, the difference may
On 11/23/2018 01:00 PM, Will Godfrey wrote:
[...]
> Thanks for going into this in such detail Robin. I never realised fp stuff
> could be *quite* so, umm, approximate!
Depending on context and the maths, the difference may not matter at
all, or may be off completely..
float a = (1 + 1e20) -
On Thu, 22 Nov 2018 23:29:11 +0100
Robin Gareus wrote:
>Hi Will,
>
>I just ran your code and -ffast-math does not make any difference.
>
>With or without --ffast-math I get "int: 5 rem: 0.049994"
>
>However optimizing the code with `-O2 --ffast-math` does make a
>difference because SSE is used.
Am 23.11.18 um 03:56 schrieb Hermann Meyer:
Am 22.11.18 um 23:44 schrieb Robin Gareus:
On 11/22/2018 09:27 PM, Hermann Meyer wrote:
However, problems with NAN's and INF's when use -ffinite-math-only
occurs only when we save preset values to file, and only sometimes
then.
A shot in the
Am 22.11.18 um 23:44 schrieb Robin Gareus:
On 11/22/2018 09:27 PM, Hermann Meyer wrote:
However, problems with NAN's and INF's when use -ffinite-math-only
occurs only when we save preset values to file, and only sometimes then.
A shot in the dark..
Serializing a float in most parts of the
On 11/22/2018 09:27 PM, Hermann Meyer wrote:
>
>
> However, problems with NAN's and INF's when use -ffinite-math-only
> occurs only when we save preset values to file, and only sometimes then.
A shot in the dark..
Serializing a float in most parts of the world uses comma as decimal
separator.
Hi Will,
I just ran your code and -ffast-math does not make any difference.
With or without --ffast-math I get "int: 5 rem: 0.049994"
However optimizing the code with `-O2 --ffast-math` does make a
difference because SSE is used.
Do you also use -O2, or -O3 along with --fast-math?
On
On Thu, Nov 22, 2018 at 09:27:58PM +0100, Hermann Meyer wrote:
> In guitarix nearly all DSP is generated by FAUST.
That doesn't make any difference for numerical stability.
This is a property of an algorithm, not of the language.
Ciao,
--
FA
___
Am 22.11.18 um 21:07 schrieb Fons Adriaensen:
On Thu, Nov 22, 2018 at 06:57:15PM +0100, Hermann Meyer wrote:
Am 22.11.18 um 18:30 schrieb Will Godfrey:
While testing some mixed floating point and integer calculations I found a
quite surprising difference when this compiler option was set
On 11/22/2018 07:28 PM, David Runge wrote:
> Rabbit hole stuff! SuperCollider came to a similar conclusion:
> https://github.com/supercollider/supercollider/issues/4116
This is a different issue. In SuperCollider's case they do want NaN and
not finite-math, that is not usually the case for
On Thu, Nov 22, 2018 at 06:57:15PM +0100, Hermann Meyer wrote:
> Am 22.11.18 um 18:30 schrieb Will Godfrey:
> > While testing some mixed floating point and integer calculations I found a
> > quite surprising difference when this compiler option was set (gcc 6.x). It
> > was
> > clearly
On Thu, 22 Nov 2018 19:28:58 +0100
David Runge wrote:
>On 2018-11-22 18:57:15 (+0100), Hermann Meyer wrote:
>> In the guitarix project we've disabled -ffast-math several years ago,
>> when I remember right it was at gcc3, as it could lead to different
>> un-reproduciable calculations. Last
On 2018-11-22 18:57:15 (+0100), Hermann Meyer wrote:
> In the guitarix project we've disabled -ffast-math several years ago,
> when I remember right it was at gcc3, as it could lead to different
> un-reproduciable calculations. Last option I've disabled on gcc8 now,
> is -ffinite-math-only, this
Am 22.11.18 um 18:30 schrieb Will Godfrey:
While testing some mixed floating point and integer calculations I found a
quite surprising difference when this compiler option was set (gcc 6.x). It was
clearly different at only 100 iterations and got dramatically worse with
larger counts.
My test
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