Why not?

src/cmd/jpg/close.c

@@ -0,0 +1,121 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+
+float c1 = 1.402;
+float c2 = 0.34414;
+float c3 = 0.71414;
+float c4 = 1.772;
+
+
+int
+closest(int Y, int Cb, int Cr)
+{
+	double r, g, b;
+	double diff, min;
+	int rgb, R, G, B, v, i;
+	int y1, cb1, cr1;
+
+	Cb -= 128;
+	Cr -= 128;
+	r = Y+c1*Cr;
+	g = Y-c2*Cb-c3*Cr;
+	b = Y+c4*Cb;
+
+//print("YCbCr: %d %d %d, RGB: %g %g %g\n", Y, Cb, Cr, r, g, b);
+
+	min = 1000000.;
+	v = 1000;
+	for(i=0; i<256; i++){
+		rgb =  cmap2rgb(i);
+		R = (rgb >> 16) & 0xFF;
+		G = (rgb >> 8) & 0xFF;
+		B = (rgb >> 0) & 0xFF;
+		diff = (R-r)*(R-r) + (G-g)*(G-g) + (B-b)*(B-b);
+//		y1 = 0.5870*G + 0.114*B + 0.299*R;
+//		cb1 = (B-y1)/1.772;
+//		cr1 = (R-y1)/1.402;
+		if(diff < min){
+//			if(Y==0 && y1!=0)
+//				continue;
+//			if(Y==256-16 && y1<256-16)
+//				continue;
+//			if(Cb==0 && cb1!=0)
+//				continue;
+//			if(Cb==256-16 && cb1<256-16)
+//				continue;
+//			if(Cr==0 && cr1!=0)
+//				continue;
+//			if(Cr==256-16 && cr1<256-16)
+//				continue;
+//print("%d %d %d\n", R, G, B);
+			min = diff;
+			v = i;
+		}
+	}
+	if(v > 255)
+		abort();
+	return v;
+}
+
+#define 	SHIFT	5
+#define	INC		(1<<SHIFT)
+
+typedef struct Color Color;
+
+struct Color
+{
+	int		col;
+	Color	*next;
+};
+
+Color	*col[INC*INC*INC];
+
+void
+add(int c, int y, int cb, int cr)
+{
+	Color *cp;
+
+	y >>= 8-SHIFT;
+	cb >>= 8-SHIFT;
+	cr >>= 8-SHIFT;
+	cp = col[cr+INC*(cb+INC*y)];
+	while(cp != nil){
+		if(cp->col == c)
+			return;
+		cp = cp->next;
+	}
+	cp = malloc(sizeof(Color));
+	cp->col = c;
+	cp->next = col[cr+INC*(cb+INC*y)];
+	col[cr+INC*(cb+INC*y)] = cp;
+}
+
+void
+main(void)
+{
+	int y, cb, cr, n;
+	Color *cp;
+
+	for(y=0; y<256; y++){
+		for(cb=0; cb<256; cb++)
+			for(cr=0;cr<256;cr++)
+				add(closest(y, cb, cr), y, cb, cr);
+		fprint(2, "%d done\n", y);
+	}
+	for(y=0; y<INC*INC*INC; y++){
+		n = 0;
+		cp = col[y];
+		while(cp != nil){
+			n++;
+			cp = cp->next;
+		}
+		cp = col[y];
+		while(cp != nil){
+			n++;
+			print("%d ", cp->col);
+			cp = cp->next;
+		}
+		print("\n");
+	}
+}