ASCIIART benchmark, C translated -> Vala translated

public class AsciiArtBenchmark : Object {
	public void benchmark() {
		int x, y, i;
		float a, b, ca, cb, t;
		string c = "0123456789ABCDEF ";

		for (y = -12; y <= 12; y++) {
			for (x = -39; x <= 39; x++) {
				a = ca = x * 0.0458f;
				b = cb = y * 0.08333f;

				for (i = 0; i <= 15; i++) {
					t = (a * a) - (b * b) + ca;
					b = (2 * a * b) + cb;
					a = t;

					if ((a * a + b * b) > 4)
						break;
				}
				stdout.printf("%s", c.substring(i, 1));
			}
			stdout.printf("\n");
		}
	}

	static void main() {
		var test = new AsciiArtBenchmark();
		test.benchmark();
	}
}