Remove multtable, replace with logical equivalent

Multtable stored the result of a 8-bit signed multiply of the upper nibble of A (interpreted as signed) and the amplitude lower nibble (interpreted as unsigned), then divided by two. On the 6510 this made sense, but in modern processors it's way faster and cleaner to simply do the multiply. Replace the render sin/sin/rect mixer with equivalent C code.
bsom · Oct 4, 2017 · 3865157 · 3865157
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commit 3865157
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diff --git a/src/RenderTabs.h b/src/RenderTabs.h
@@ -263,43 +263,6 @@ unsigned char rectangle[] =
 };
 
 
-//tab42752
-unsigned char multtable[] =
-{
-	0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 ,
-	0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 , 0x00 ,
-	0x00 , 0x00 , 1 , 1 , 2 , 2 , 3 , 3 ,
-	4 , 4 , 5 , 5 , 6 , 6 , 7 , 7 ,
-	0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 ,
-	8 , 9 ,0xA ,0xB ,0xC ,0xD ,0xE ,0xF ,
-	0x00 , 1 , 3 , 4 , 6 , 7 , 9 ,0xA ,
-	0xC ,0xD ,0xF , 0x10 , 0x12 , 0x13 , 0x15 , 0x16 ,
-	0x00 , 2 , 4 , 6 , 8 ,0xA ,0xC ,0xE ,
-	0x10 , 0x12 , 0x14 , 0x16 , 0x18 , 0x1A , 0x1C , 0x1E ,
-	0x00 , 2 , 5 , 7 ,0xA ,0xC ,0xF , 0x11 ,
-	0x14 , 0x16 , 0x19 , 0x1B , 0x1E , 0x20 , 0x23 , 0x25 ,
-	0x00 , 3 , 6 , 9 ,0xC ,0xF , 0x12 , 0x15 ,
-	0x18 , 0x1B , 0x1E , 0x21 , 0x24 , 0x27 , 0x2A , 0x2D ,
-	0x00 , 0x03 , 0x07 , 0x0A , 0x0E , 0x11 , 0x15 , 0x18 ,
-	0x1C , 0x1F , 0x23 , 0x26 , 0x2A , 0x2D , 0x31 , 0x34 ,
-	0x00 , 0xFC , 0xF8 , 0xF4 , 0xF0 , 0xEC , 0xE8 , 0xE4 ,
-	0xE0 , 0xDC , 0xD8 , 0xD4 , 0xD0 , 0xCC , 0xC8 , 0xC4 ,
-	0x00 , 0xFC , 0xF9 , 0xF5 , 0xF2 , 0xEE , 0xEB , 0xE7 ,
-	0xE4 , 0xE0 , 0xDD , 0xD9 , 0xD6 , 0xD2 , 0xCF , 0xCB ,
-	0x00 , 0xFD , 0xFA , 0xF7 , 0xF4 , 0xF1 , 0xEE , 0xEB ,
-	0xE8 , 0xE5 , 0xE2 , 0xDF , 0xDC , 0xD9 , 0xD6 , 0xD3 ,
-	0x00 , 0xFD , 0xFB , 0xF8 , 0xF6 , 0xF3 , 0xF1 , 0xEE ,
-	0xEC , 0xE9 , 0xE7 , 0xE4 , 0xE2 , 0xDF , 0xDD , 0xDA ,
-	0x00 , 0xFE , 0xFC , 0xFA , 0xF8 , 0xF6 , 0xF4 , 0xF2 ,
-	0xF0 , 0xEE , 0xEC , 0xEA , 0xE8 , 0xE6 , 0xE4 , 0xE2 ,
-	0x00 , 0xFE , 0xFD , 0xFB , 0xFA , 0xF8 , 0xF7 , 0xF5 ,
-	0xF4 , 0xF2 , 0xF1 , 0xEF , 0xEE , 0xEC , 0xEB , 0xE9 ,
-	0x00 , 0xFF , 0xFE , 0xFD , 0xFC , 0xFB , 0xFA , 0xF9 ,
-	0xF8 , 0xF7 , 0xF6 , 0xF5 , 0xF4 , 0xF3 , 0xF2 , 0xF1 ,
-	0x00 , 0xFF , 0xFF , 0xFE , 0xFE , 0xFD , 0xFD , 0xFC ,
-	0xFC , 0xFB , 0xFB , 0xFA , 0xFA , 0xF9 , 0xF9 , 0xF8
-};
-
 //random data ?
 unsigned char sampleTable[0x500] =
 {

diff --git a/src/render.c b/src/render.c
@@ -361,7 +361,6 @@ void Render()
 	unsigned char speedcounter; //mem45
 	unsigned char mem48;
 	int i;
-	int carry;
 	if (phonemeIndexOutput[0] == 255) return; //exit if no data
 
 	A = 0;
@@ -806,13 +805,16 @@ if (debug)
 		} else
 		{
             // simulate the glottal pulse and formants
-			mem56 = multtable[sinus[phase1] | amplitude1[Y]];
-
-			carry = 0;
-			if ((mem56+multtable[sinus[phase2] | amplitude2[Y]] ) > 255) carry = 1;
-			mem56 += multtable[sinus[phase2] | amplitude2[Y]];
-			A = mem56 + multtable[rectangle[phase3] | amplitude3[Y]] + (carry?1:0);
-			A = ((A + 136) & 255) >> 4; //there must be also a carry
+			signed char sp1 = (signed char)sinus[phase1];
+			signed char sp2 = (signed char)sinus[phase2];
+			signed char rp3 = (signed char)rectangle[phase3];
+			signed int sin1 = sp1 * ((unsigned char)amplitude1[Y] & 0x0f);
+			signed int sin2 = sp2 * ((unsigned char)amplitude2[Y] & 0x0f);
+			signed int rect = rp3 * ((unsigned char)amplitude3[Y] & 0x0f);
+			signed int mux = sin1 + sin2 + rect;
+			mux /= 32;
+			mux += 128; // Go from signed to unsigned amplitude
+			A = (mux>>4) & 0x0f;
 			//mem[54296] = A;
 
 			// output the accumulated value