Subject: Re: [linux-audio-dev] swh plugins and fixing undenormalize
From: Steve Harris (S.W.Harris_AT_ecs.soton.ac.uk)
Date: Thu Jun 24 2004 - 12:17:53 EEST
On Thu, Jun 24, 2004 at 05:31:30 +1000, Erik de Castro Lopo wrote:
> Since the problem is denormalised numbers, has anybody thought of
> adding a small DC offset (1e-15) or alternating the addition/subraction
> of a small value?
Yes. I use it in some places.
The problem with addition is that denormals tend to bite in feedback
loops, where DC offsets are a bit of a pain.
You can do
y += delta
y -= delta
but youre at the mercy of the optimiser.
> If I had a spare couple of hours I'd benchmark it myself.
There is some stuff online about it.
A C99 safe version of the obove macro (with a bit of extension, to catch
"P4 denormals") is:
typedef union {
float f;
int32_t i;
} ls_pcast32;
static inline float flush_to_zero(float f)
{
ls_pcast32 v;
v.f = f;
// original: return (v.i & 0x7f800000) == 0 ? 0.0f : f;
// version from Tim Blechmann:
return (v.i & 0x7f800000) < 0x08000000 ? 0.0f : f;
}
- Steve
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