From 2886dd1daee27eac5f0dcc002588700a54014afe Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 21 Apr 2020 20:19:02 -0400
Subject: [PATCH] Collapses key-level scaling to a single 2d table.

I dare imagine I can do better; the columns in particular look like arithmetic progressions.
---
 Components/OPL2/Implementation/Operator.cpp | 56 +++++----------------
 1 file changed, 13 insertions(+), 43 deletions(-)

diff --git a/Components/OPL2/Implementation/Operator.cpp b/Components/OPL2/Implementation/Operator.cpp
index 667518ca2..57824c9f3 100644
--- a/Components/OPL2/Implementation/Operator.cpp
+++ b/Components/OPL2/Implementation/Operator.cpp
@@ -177,53 +177,23 @@ void Operator::update(OperatorState &state, bool key_on, int channel_period, int
 	// Calculate key-level scaling. Table is as per p14 of the YM3812 application manual,
 	// converted into a fixed-point scheme. Compare with https://www.smspower.org/Development/RE12
 	// and apologies for the highly ad hoc indentation.
-	constexpr int key_level_scales[4][8][16] = {
+	constexpr int key_level_scale_shifts[4] = {7, 1, 2, 0};	// '7' is just a number large enough to render all the numbers below as 0.
+	constexpr int key_level_scales[8][16] = {
 #define _ 0
-		{	// 0 db of attenuation.
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-			{_,	_, _, _, _, _, _, _, _, _, _, _, _, _, _, _},
-		},
-		{	// 3 db.
-			{_,	 _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _},
-			{_,  _,  _,  _,  _,  _,  _,  _,  _,  2,  3,  4,  5,  6,  7,  8},
-			{_,  _,  _,  _,  _,  3,  5,  7,  8, 10, 11, 12, 13, 14, 15, 16},
-			{_,  _,  _,  5,  8, 11, 13, 15, 16, 18, 19, 20, 21, 22, 23, 24},
-			{_,	 _,  8, 13, 16, 19, 21, 23, 24, 26, 27, 28, 29, 30, 31, 32},
-			{_,	 8, 16, 21, 24, 27, 29, 31, 32, 34, 35, 36, 37, 38, 39, 40},
-			{_,	16, 24, 29, 32, 35, 37, 39, 40, 42, 43, 44, 45, 46, 47, 48},
-			{_,	24, 32, 37, 40, 43, 45, 47, 48, 50, 51, 52, 53, 54, 55, 56},
-		},
-		{	// 1.5 db.
-			{_,	 _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _,  _},
-			{_,  _,  _,  _,  _,  _,  _,  _,  _,  1,  1,  2,  2,  3,  3,  4},
-			{_,  _,  _,  _,  _,  1,  2,  3,  4,  5,  5,  6,  6,  7,  7,  8},
-			{_,  _,  _,  2,  4,  5,  6,  7,  8,  9,  9, 10, 10, 11, 11, 12},
-			{_,	 _,  4,  6,  8,  9, 10, 11, 12, 13, 13, 14, 14, 15, 15, 16},
-			{_,	 4,  8, 10, 12, 13, 14, 15, 16, 17, 17, 18, 18, 19, 19, 20},
-			{_,	 8, 12, 14, 16, 17, 18, 19, 20, 21, 21, 22, 22, 23, 23, 24},
-			{_,	12, 16, 18, 20, 21, 22, 23, 24, 25, 25, 26, 26, 27, 27, 28},
-		},
-		{	// 6 db.
-			{_,	  _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _},
-			{_,   _,   _,   _,   _,   _,   _,   _,   _,   4,   6,   8,  10,  12,  14,  16},
-			{_,   _,   _,   _,   _,   6,  10,  14,  16,  20,  22,  24,  26,  28,  30,  32},
-			{_,   _,   _,  10,  16,  22,  26,  30,  32,  36,  38,  40,  42,  44,  46,  48},
-			{_,	  _,  16,  26,  32,  38,  42,  46,  48,  52,  54,  56,  58,  60,  62,  64},
-			{_,	 16,  32,  42,  48,  54,  58,  62,  64,  68,  70,  72,  74,  76,  78,  80},
-			{_,	 32,  48,  58,  64,  70,  74,  78,  80,  84,  86,  88,  90,  92,  94,  96},
-			{_,	 48,  64,  74,  80,  86,  90,  94,  96, 100, 102, 104, 106, 108, 110, 112},
-		},
+		// 6 db attenuations.
+		{_,	  _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _,   _},
+		{_,   _,   _,   _,   _,   _,   _,   _,   _,   4,   6,   8,  10,  12,  14,  16},
+		{_,   _,   _,   _,   _,   6,  10,  14,  16,  20,  22,  24,  26,  28,  30,  32},
+		{_,   _,   _,  10,  16,  22,  26,  30,  32,  36,  38,  40,  42,  44,  46,  48},
+		{_,	  _,  16,  26,  32,  38,  42,  46,  48,  52,  54,  56,  58,  60,  62,  64},
+		{_,	 16,  32,  42,  48,  54,  58,  62,  64,  68,  70,  72,  74,  76,  78,  80},
+		{_,	 32,  48,  58,  64,  70,  74,  78,  80,  84,  86,  88,  90,  92,  94,  96},
+		{_,	 48,  64,  74,  80,  86,  90,  94,  96, 100, 102, 104, 106, 108, 110, 112},
 #undef _
 	};
-	assert((channel_period >> 6) < 4);
+	assert((channel_period >> 6) < 16);
 	assert(channel_octave < 8);
-	state.attenuation.log += key_level_scales[key_level_scaling_][channel_octave][channel_period >> 6] << 7;
+	state.attenuation.log += (key_level_scales[channel_octave][channel_period >> 6] >> key_level_scale_shifts[key_level_scaling_]) << 7;
 
 	// Combine the ADSR attenuation and overall channel attenuation.
 	if(overrides) {