Why not?

src/cmd/jpg/rgbrgbv.c

@@ -0,0 +1,69 @@
+#include <u.h>
+#include <libc.h>
+#include <draw.h>
+
+/*
+ * This version of closest() is now (feb 20, 2001) installed as rgb2cmap in libdraw
+ */
+
+int
+closest(int cr, int cg, int cb)
+{
+	int i, r, g, b, sq;
+	ulong rgb;
+	int best, bestsq;
+
+	best = 0;
+	bestsq = 0x7FFFFFFF;
+	for(i=0; i<256; i++){
+		rgb = cmap2rgb(i);
+		r = (rgb>>16) & 0xFF;
+		g = (rgb>>8) & 0xFF;
+		b = (rgb>>0) & 0xFF;
+		sq = (r-cr)*(r-cr)+(g-cg)*(g-cg)+(b-cb)*(b-cb);
+		if(sq < bestsq){
+			bestsq = sq;
+			best = i;
+		}
+	}
+	return best;
+}
+
+void
+main(int argc, char *argv[])
+{
+	int i, rgb;
+	int r, g, b;
+	uchar close[16*16*16];
+
+	/* rgbmap */
+	print("uint rgbmap[256] = {\n");
+	for(i=0; i<256; i++){
+		if(i%8 == 0)
+			print("\t");
+		rgb = cmap2rgb(i);
+		r = (rgb>>16) & 0xFF;
+		g = (rgb>>8) & 0xFF;
+		b = (rgb>>0) & 0xFF;
+		print("0x%.6ulX, ", (r<<16) | (g<<8) | b);
+		if(i%8 == 7)
+			print("\n");
+	}
+	print("};\n\n");
+
+	/* closestrgb */
+	print("uchar closestrgb[16*16*16] = {\n");
+	for(r=0; r<256; r+=16)
+	for(g=0; g<256; g+=16)
+	for(b=0; b<256; b+=16)
+		close[(b/16)+16*((g/16)+16*(r/16))] = closest(r+8, g+8, b+8);
+	for(i=0; i<16*16*16; i++){
+		if(i%16 == 0)
+			print("\t");
+		print("%d,", close[i]);
+		if(i%16 == 15)
+			print("\n");
+	}
+	print("};\n\n");
+	exits(nil);
+}