MT-32: Sync with the latest changes in munt

This syncs our code with munt commits 3f0db2d and 2c5f314

3 files changed, 16 insertions, 23 deletions

diff --git a/audio/softsynth/mt32/Partial.cpp b/audio/softsynth/mt32/Partial.cpp
index 58878a3513..a4d1ab03fa 100644
--- a/audio/softsynth/mt32/Partial.cpp
+++ b/audio/softsynth/mt32/Partial.cpp
@@ -284,8 +284,12 @@ unsigned long Partial::generateSamples(float *partialBuf, unsigned long length)
 			// res corresponds to a value set in an LA32 register
 			Bit8u res = patchCache->srcPartial.tvf.resonance + 1;
 
-			// Using tiny exact table for computation of EXP2F(1.0f - (32 - res) / 4.0f)
-			float resAmp = tables.resAmpMax[res];
+			float resAmp;
+			{
+				// resAmp = EXP2F(1.0f - (32 - res) / 4.0f);
+				static const float resAmpFactor = EXP2F(-7);
+				resAmp = EXP2I(res << 10) * resAmpFactor;
+			}
 
 			// The cutoffModifier may not be supposed to be directly added to the cutoff -
 			// it may for example need to be multiplied in some way.
@@ -317,23 +321,26 @@ unsigned long Partial::generateSamples(float *partialBuf, unsigned long length)
 				relWavePos -= waveLen;
 			}
 
+			// Ratio of positive segment to wave length
 			float pulseLen = 0.5f;
 			if (pulseWidthVal > 128) {
-				pulseLen += tables.pulseLenFactor[pulseWidthVal - 128];
+				// pulseLen = EXP2F((64 - pulseWidthVal) / 64);
+				static const float pulseLenFactor = EXP2F(-192 / 64);
+				pulseLen = EXP2I((256 - pulseWidthVal) << 6) * pulseLenFactor;
 			}
 			pulseLen *= waveLen;
 
-			float lLen = pulseLen - cosineLen;
+			float hLen = pulseLen - cosineLen;
 
 			// Ignore pulsewidths too high for given freq
-			if (lLen < 0.0f) {
-				lLen = 0.0f;
+			if (hLen < 0.0f) {
+				hLen = 0.0f;
 			}
 
 			// Ignore pulsewidths too high for given freq and cutoff
-			float hLen = waveLen - lLen - 2 * cosineLen;
-			if (hLen < 0.0f) {
-				hLen = 0.0f;
+			float lLen = waveLen - hLen - 2 * cosineLen;
+			if (lLen < 0.0f) {
+				lLen = 0.0f;
 			}
 
 			// Correct resAmp for cutoff in range 50..66
diff --git a/audio/softsynth/mt32/Tables.cpp b/audio/softsynth/mt32/Tables.cpp
index b6e63840bc..5353a74079 100644
--- a/audio/softsynth/mt32/Tables.cpp
+++ b/audio/softsynth/mt32/Tables.cpp
@@ -72,24 +72,12 @@ Tables::Tables() {
 		//synth->printDebug("%d: %d", i, pulseWidth100To255[i]);
 	}
 
-	// Ratio of negative segment to wave length
-	for (int i = 0; i < 128; i++) {
-		// Formula determined from sample analysis.
-		float pt = 0.5f / 127.0f * i;
-		pulseLenFactor[i] = (1.241857812f - pt) * pt;    // seems to be 2 ^ (5 / 16) = 1.241857812f
-	}
-
 	// The LA32 chip presumably has such a table inside as the internal computaions seem to be performed using fixed point math with 12-bit fractions
 	for (int i = 0; i < 4096; i++) {
 		exp2[i] = EXP2F(i / 4096.0f);
 	}
 
 	// found from sample analysis
-	for (int i = 0; i < 32; i++) {
-		resAmpMax[i] = EXP2F(1.0f - (32 - i) / 4.0f);
-	}
-
-	// found from sample analysis
 	resAmpFadeFactor[7] = 1.0f / 8.0f;
 	resAmpFadeFactor[6] = 2.0f / 8.0f;
 	resAmpFadeFactor[5] = 3.0f / 8.0f;
diff --git a/audio/softsynth/mt32/Tables.h b/audio/softsynth/mt32/Tables.h
index b353cf4c51..c3e80e7e9b 100644
--- a/audio/softsynth/mt32/Tables.h
+++ b/audio/softsynth/mt32/Tables.h
@@ -57,8 +57,6 @@ public:
 	Bit8u pulseWidth100To255[101];
 
 	float exp2[4096];
-	float pulseLenFactor[128];
-	float resAmpMax[32];
 	float resAmpFadeFactor[8];
 	float sinf10[5120];
 };