From c6529888fd1c476842d9985cfd54cdf33271f9ef Mon Sep 17 00:00:00 2001
From: Chris Moeller <kode54@gmail.com>
Date: Thu, 31 Oct 2013 18:20:58 -0700
Subject: [PATCH] Hard limit only if output would clip, and use a table for up
 to 2x volume level

---
 Frameworks/GME/gme/Spc_Filter.cpp | 35 +++++++++++++++++++++++--------
 Frameworks/GME/gme/Spc_Filter.h   |  4 ++++
 2 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/Frameworks/GME/gme/Spc_Filter.cpp b/Frameworks/GME/gme/Spc_Filter.cpp
index c4e56a19b..87b38fae6 100644
--- a/Frameworks/GME/gme/Spc_Filter.cpp
+++ b/Frameworks/GME/gme/Spc_Filter.cpp
@@ -22,15 +22,31 @@ static const float limiter_max_05 = (float)(limiter_max - 0.5);
 
 static short hard_limit_sample( int sample )
 {
-	double val = (double)sample * (1.0 / 32768.0);
-	if (val < -0.5)
-		val = (tanh((val + 0.5) / limiter_max_05) * limiter_max_05 - 0.5);
-	else if (val > 0.5)
-		val = (tanh((val - 0.5) / limiter_max_05) * limiter_max_05 + 0.5);
-	return val * 32768.0;
+    double val = (double)sample * (1.0 / 32768.0);
+    if (val < -0.5)
+        val = (tanh((val + 0.5) / limiter_max_05) * limiter_max_05 - 0.5);
+    else if (val > 0.5)
+        val = (tanh((val - 0.5) / limiter_max_05) * limiter_max_05 + 0.5);
+    return val * 32768.0;
 }
 
-void Spc_Filter::clear() { memset( ch, 0, sizeof ch ); }
+void Spc_Filter::build_limit_table()
+{
+    for (int i = -65536; i < 65536; ++i)
+    {
+        hard_limit_table[ i + 65536 ] = hard_limit_sample( i );
+    }
+}
+
+inline short Spc_Filter::limit_sample(int sample)
+{
+    if (!limiting && ((unsigned)sample + 32768) < 65536) return sample;
+    limiting = true;
+    if (((unsigned)sample + 65536) < 131072) return hard_limit_table[ sample + 65536 ];
+    return hard_limit_sample( sample );
+}
+
+void Spc_Filter::clear() { limiting = false; memset( ch, 0, sizeof ch ); }
 
 Spc_Filter::Spc_Filter()
 {
@@ -38,6 +54,7 @@ Spc_Filter::Spc_Filter()
 	gain    = gain_unit;
 	bass    = bass_norm;
 	clear();
+    build_limit_table();
 }
 
 void Spc_Filter::run( short io [], int count )
@@ -68,7 +85,7 @@ void Spc_Filter::run( short io [], int count )
 				int s = sum >> (gain_bits + 2);
 				sum += (delta * gain) - (sum >> bass);
 
-				io [i] = hard_limit_sample( s );
+				io [i] = limit_sample( s );
 			}
 			
 			c->p1  = p1;
@@ -84,7 +101,7 @@ void Spc_Filter::run( short io [], int count )
 		while ( io < end )
 		{
 			int s = (*io * gain) >> gain_bits;
-			*io++ = hard_limit_sample( s );
+			*io++ = limit_sample( s );
 		}
 	}
 }
diff --git a/Frameworks/GME/gme/Spc_Filter.h b/Frameworks/GME/gme/Spc_Filter.h
index 06758c971..26653de10 100644
--- a/Frameworks/GME/gme/Spc_Filter.h
+++ b/Frameworks/GME/gme/Spc_Filter.h
@@ -40,8 +40,12 @@ private:
 	int gain;
 	int bass;
 	bool enabled;
+    bool limiting;
 	struct chan_t { int p1, pp1, sum; };
 	chan_t ch [2];
+    short hard_limit_table[131072];
+    void build_limit_table();
+    inline short limit_sample(int sample);
 };
 
 inline void Spc_Filter::enable( bool b )  { enabled = b; }