Add single color table generation code.

data/bugs/85/tables.cpp

@@ -0,0 +1,95 @@
+
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef unsigned char uint8;
+
+
+static int Mul8Bit(int a, int b)
+{
+	int t = a * b + 128;
+	return (t + (t >> 8)) >> 8;
+}
+
+// this exactly matches the (fm*2 + to)/3
+static inline int Lerp13_16bit(int fm, int to)
+{
+	int t = fm * (2 * 0xAAAB) + to * 0xAAAB;
+	return t >> 17;
+}
+
+static inline int Lerp13(int fm, int to)
+{
+	return (fm * 2 + to) / 3;
+}
+
+
+static void PrepareOptTable(uint8 * Table, const uint8 * expand, int size)
+{
+	for (int i = 0; i < 256; i++)
+	{
+		float bestErr = 256;
+
+		for (int min = 0; min < size; min++)
+		{
+			for (int max = 0; max < size; max++)
+			{
+				int mine = expand[min];
+				int maxe = expand[max];
+				//if (maxe - mine < 32)
+				{
+					//printf("%d <-> %d\n", maxe + Mul8Bit(mine-maxe, 0x55), Lerp13(maxe, mine));
+					//int err = abs(Lerp13_16bit(mine, maxe) - i);
+					//int err = abs(maxe + Mul8Bit(mine-maxe, 0x55) - i);
+					float err = abs(Lerp13(maxe, mine) - i);
+					//err += 0.03f * abs(maxe - mine);
+					err += 0.03f * abs(max - min);
+
+					if (err < bestErr)
+					{
+						Table[i*2+0] = max;
+						Table[i*2+1] = min;
+						bestErr = err;
+					}
+				}
+			}
+		}
+		printf("%d: %f %d\n", i, bestErr, abs(Table[i*2+0] - Table[i*2+1]));
+	}
+}
+
+
+int main()
+{
+	uint8 OMatch5[256*2];
+	uint8 OMatch6[256*2];
+	
+	uint8 Expand5[32];
+	uint8 Expand6[64];
+
+	for (int i=0; i<32; i++)
+		Expand5[i] = (i<<3)|(i>>2);
+
+	for (int i=0; i<64; i++)
+		Expand6[i] = (i<<2)|(i>>4);
+
+	PrepareOptTable(OMatch5, Expand5, 32);
+	PrepareOptTable(OMatch6, Expand6, 64);
+
+	printf("const static uint8 OMatch5[256][2] = {\n");
+	for (int i = 0; i < 256; i++)
+	{
+		printf("\t{0x%.2X, 0x%.2X},\n", OMatch5[2*i+0], OMatch5[2*i+1]);
+	}
+	printf("}\n");
+
+	printf("const static uint8 OMatch6[256][2] = {\n");
+	for (int i = 0; i < 256; i++)
+	{
+		printf("\t{0x%.2X, 0x%.2X},\n", OMatch6[2*i+0], OMatch6[2*i+1]);
+	}
+	printf("}\n");
+
+	return 0;
+}
+