[PD] Raspberry Pi does denormals

[Pierre Massat]

Hi,

Could someone please explain how this impacts Pd's performance on the
Raspberry Pi ?
It doesn't make any sense to me right now, but i'm very curious...

Cheers,

Pierre.

2013/1/20 Hans-Christoph Steiner <hans at at.or.at>

>
> I think this is what you want, from 'man gcc'.  Its interesting to note
> that
> the NEON mode, which provides SIMD, also does not do denormals:
>
> -mfpu=name
> -mfpe=number
> -mfp=number
>     This specifies what floating point hardware (or hardware emulation) is
>     available on the target.  Permissible names are: fpa, fpe2, fpe3,
> maverick,
>     vfp, vfpv3, vfpv3-fp16, vfpv3-d16, vfpv3-d16-fp16, vfpv3xd,
> vfpv3xd-fp16,
>     neon, neon-fp16, vfpv4, vfpv4-d16, fpv4-sp-d16 and neon-vfpv4.  -mfp
> and
>     -mfpe are synonyms for -mfpu=fpenumber, for compatibility with older
>     versions of GCC.
>
>     If -msoft-float is specified this specifies the format of floating
> point
>     values.
>
>     If the selected floating-point hardware includes the NEON extension
> (e.g.
>     -mfpu=neon), note that floating-point operations will not be used by
> GCC's
>     auto-vectorization pass unless -funsafe-math-optimizations is also
>     specified.  This is because NEON hardware does not fully implement the
> IEEE
>     754 standard for floating-point arithmetic (in particular denormal
> values
>     are treated as zero), so the use of NEON instructions may lead to a
> loss of
>     precision.
>
>
> .hc
>
> On 01/20/2013 06:54 AM, katja wrote:
> > I was assuming, or maybe just hoping? that Raspberry Pi (and ARM
> > devices in general) would not suffer from Denormal's disease like
> > Intel processors do. But guess what: Pi's float coprocessor is IEEE
> > 754 compliant and does all denormals by default (can check with
> > attached denorm-test.pd). Bummer! As if one would use an ARM device to
> > calculate the size of a Majorana particle, rather than doing simple
> > dsp. Do we really need to enable PD-BIGORSMALL() checks for this poor
> > little processor? There seems to be something called 'RunFast mode'
> > for Pi's float processor vfpv2, but I see no way how to enable this
> > via gcc. Option -ffast-math is allowed but doesn't do the trick. Can't
> > find an option to set vfpv2 specifically, in gcc docs.
> >
> > Katja
> >
> >
> >
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