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diff --git a/docs/history/17-o3-boundaries/code/examples/mandel.zc b/docs/history/17-o3-boundaries/code/examples/mandel.zc
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+// the mandelbrot set in 16.16 fixed point. the cpu has no fixed-point
+// multiply, so one gets wired in: a 32x32 -> 64 bit multiply, keeping the
+// middle 32 bits. the jit inlines it as two native multiplies and a shift.
+enhance fmul(a, b) micro
+	"r2 = mul a b; r3 = mulhs a b"
+	"; r3 = shl r3 16; r2 = shr r2 16; a = or r3 r2";
+
+const ONE = 65536, W = 72, H = 28, MAXIT = 40;
+let shades = " .,:;-=+*%#@";
+
+int escape(int cx, int cy) {
+	int x = 0, y = 0, i = 0;
+	while (i < MAXIT) {
+		int xx = fmul(x, x), yy = fmul(y, y);
+		if (xx + yy > 4 * ONE) return i;
+		y = 2 * fmul(x, y) + cy;
+		x = xx - yy + cx;
+		i++;
+	}
+	return MAXIT;
+}
+fn main()
+{
+	int row = 0;
+	while (row < H) {
+		int col = 0, cy = (row * 2400 / (H - 1) - 1200) * ONE / 1000;
+		while (col < W) {
+			int cx = (col * 3200 / (W - 1) - 2200) * ONE / 1000, it = escape(cx, cy);
+			putc(it == MAXIT ? '@' : shades[it * 11 / MAXIT]);
+			col++;
+		}
+		putc(10);
+		row++;
+	}
+	return 0;
+}