From 54ece22efbb1bcb9784e30021c71d4749d8bd3a7 Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Mon, 8 Mar 2021 22:19:01 +0100
Subject: [PATCH] Prevent denormals in Lua DSP state (LPF, Biquad)

---
 libs/ardour/dsp_filter.cc | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libs/ardour/dsp_filter.cc b/libs/ardour/dsp_filter.cc
index 8fb572729f..8ff5a35033 100644
--- a/libs/ardour/dsp_filter.cc
+++ b/libs/ardour/dsp_filter.cc
@@ -20,6 +20,8 @@
 #include <algorithm>
 #include <stdlib.h>
 #include <cmath>
+#include <boost/math/special_functions/fpclassify.hpp>
+
 #include "ardour/dB.h"
 #include "ardour/buffer.h"
 #include "ardour/dsp_filter.h"
@@ -125,6 +127,7 @@ LowPass::proc (float *data, const uint32_t n_samples)
 	}
 	_z = z;
 	if (!isfinite_local (_z)) { _z = 0; }
+	else if (!boost::math::isnormal (_z)) { _z = 0; }
 }
 
 void
@@ -178,7 +181,9 @@ Biquad::run (float *data, const uint32_t n_samples)
 	}
 
 	if (!isfinite_local (_z1)) { _z1 = 0; }
+	else if (!boost::math::isnormal (_z1)) { _z1 = 0; }
 	if (!isfinite_local (_z2)) { _z2 = 0; }
+	else if (!boost::math::isnormal (_z2)) { _z2 = 0; }
 }
 
 void