I wonder if this line, right after you check "in" for denormality, might
not be causing trouble:
// very slight waveshape for extra stability
sv->b = sv->b - sv->b * sv->b * sv->b * 0.001f;
Since cubing a tiny number and multiplying it by .001 could end up
creating a denormal, which isn't checked for until it's gone through a
series of further computations and ends up as the new "in".
Also (I don't really know), I thought that denormals were caught as a
processor exception whenever they occurred, so neutralizing them in the
code after the fact won't do anything to speed up the process, except to
prevent a cascade of denormals. The thing to do would be to replace the
exception handler with your own.
A bunch of interesting stuff here:
http://software.intel.com/en-us/articles/x87-and-sse-floating-point-assists-in-ia-32-flush-to-zero-ftz-and-denormals-are-zero-daz/
....where the conclusion reads:
"To avoid serialization and performance issues due to denormals and
underflow numbers, use the SSE and SSE2 instructions to set
Flush-to-Zero and Denormals-Are-Zero modes within the hardware to enable
highest performance for floating-point applications."
Martin
Ed Kelly wrote:
Hi Damon,
I have tried to implement this technique, to fix the svf~ and I am still
getting denormal errors pegging the CPU. Is there anything I have missed do you
think? After reading a little bit about unions and uint32_t I think I've used
them correctly...
If this bug can be zapped for good then I'd like to eliminate denormal errors
from the svn for good!
Best,
Ed
--- On Fri, 14/8/09, Damon Chaplin <[email protected]> wrote:
From: Damon Chaplin <[email protected]>
Subject: Re: [PD-dev] denormals: svf, freeverb (was Re: [PD] bug in freeverb???)
To: "Ed Kelly" <[email protected]>
Cc: "PD List" <[email protected]>, "pddev" <[email protected]>
Date: Friday, 14 August, 2009, 1:51 PM
On Fri, 2009-08-14 at 13:06 +0100, Damon Chaplin wrote:
On Fri, 2009-08-14 at 13:03 +0100, Damon Chaplin
wrote:
if (u.int_value &
0x7f800000)
fv = 0.0f;
Oops. That should be:
if (u.int_value & 0x7f800000 == 0)
fv = 0.0f;
Or even better:
if ((u.int_value & 0x7f800000) == 0)
fv = 0.0f;
Damon
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