From c02169a6c8ba7cd9b9b06f8670187bdbced8283a Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Mon, 18 Jan 2021 15:29:13 +0100
Subject: [PATCH] Micro-optimization: pre-calculate pan-law

powf() is very expensive to call, and as long as the pan-law
is fixed, there is no need to re-calculate coefficient scale
factor on every update.
---
 libs/panners/1in2out/panner_1in2out.cc | 13 ++++++++++---
 libs/panners/2in2out/panner_2in2out.cc | 10 +++++++++-
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/libs/panners/1in2out/panner_1in2out.cc b/libs/panners/1in2out/panner_1in2out.cc
index 8cf6b70e0c..14e9d614af 100644
--- a/libs/panners/1in2out/panner_1in2out.cc
+++ b/libs/panners/1in2out/panner_1in2out.cc
@@ -101,12 +101,15 @@ Panner1in2out::~Panner1in2out ()
 void
 Panner1in2out::update ()
 {
-	float       panR, panL;
+#if 0
 	float const pan_law_attenuation = -3.0f;
 	float const scale               = 2.0f - 4.0f * powf (10.0f, pan_law_attenuation / 20.0f);
+#else
+	float const scale               = -0.831783138f;
+#endif
 
-	panR = _pannable->pan_azimuth_control->get_value ();
-	panL = 1 - panR;
+	float const panR = _pannable->pan_azimuth_control->get_value ();
+	float const panL = 1 - panR;
 
 	desired_left  = panL * (scale * panL + 1.0f - scale);
 	desired_right = panR * (scale * panR + 1.0f - scale);
@@ -275,8 +278,12 @@ Panner1in2out::distribute_one_automated (AudioBuffer& srcbuf, BufferSet& obufs,
 	   each buffer (output)
 	*/
 
+#if 0
 	const float pan_law_attenuation = -3.0f;
 	const float scale               = 2.0f - 4.0f * powf (10.0f, pan_law_attenuation / 20.0f);
+#else
+	float const scale               = -0.831783138f;
+#endif
 
 	for (pframes_t n = 0; n < nframes; ++n) {
 		float       panR = position[n];
diff --git a/libs/panners/2in2out/panner_2in2out.cc b/libs/panners/2in2out/panner_2in2out.cc
index e7c1365e46..0664bc63cd 100644
--- a/libs/panners/2in2out/panner_2in2out.cc
+++ b/libs/panners/2in2out/panner_2in2out.cc
@@ -184,9 +184,13 @@ Panner2in2out::update ()
 	}
 
 	/* compute target gain coefficients for both input signals */
-
+#if 0
 	float const pan_law_attenuation = -3.0f;
 	float const scale               = 2.0f - 4.0f * powf (10.0f, pan_law_attenuation / 20.0f);
+#else
+	float const scale               = -0.831783138f;
+#endif
+
 	float       panR;
 	float       panL;
 
@@ -408,8 +412,12 @@ Panner2in2out::distribute_one_automated (AudioBuffer& srcbuf, BufferSet& obufs,
 	 * each buffer (output)
 	*/
 
+#if 0
 	const float pan_law_attenuation = -3.0f;
 	const float scale               = 2.0f - 4.0f * powf (10.0f, pan_law_attenuation / 20.0f);
+#else
+	float const scale               = -0.831783138f;
+#endif
 
 	for (pframes_t n = 0; n < nframes; ++n) {
 		float panR;