AlphabetEncoder

src/main/java/org/apache/sysds/hops/rewriter/RewriterAlphabetEncoder.java

@@ -0,0 +1,34 @@
+package org.apache.sysds.hops.rewriter;
+
+public class RewriterAlphabetEncoder {
+
+	public static int[] fromBaseNNumber(int l, int n) {
+		if (l == 0)
+			return new int[] { 0 };
+
+		int numDigits = (int)(Math.log(l) / Math.log(n)) + 1;
+		int[] digits = new int[numDigits];
+
+		for (int i = numDigits - 1; i >= 0; i--) {
+			digits[i] = l % n;
+			l = l / n;
+		}
+
+		return digits;
+	}
+
+	public static int toBaseNNumber(int[] digits, int n) {
+		if (digits.length == 0)
+			throw new IllegalArgumentException();
+
+		int multiplicator = 1;
+		int out = 0;
+
+		for (int i = digits.length - 1; i >= 0; i--) {
+			out += multiplicator * digits[i];
+			multiplicator *= n;
+		}
+
+		return out;
+	}
+}

src/test/java/org/apache/sysds/test/component/codegen/rewrite/functions/RewriterAlphabetTest.java

@@ -0,0 +1,24 @@
+package org.apache.sysds.test.component.codegen.rewrite.functions;
+
+import org.apache.sysds.hops.rewriter.RewriterAlphabetEncoder;
+import org.junit.Test;
+
+public class RewriterAlphabetTest {
+
+	@Test
+	public void testDecode1() {
+		int l = 27;
+		int n = 5;
+		int[] digits = RewriterAlphabetEncoder.fromBaseNNumber(l, n);
+		assert digits.length == 3 && digits[0] == 1 && digits[1] == 0 && digits[2] == 2;
+	}
+
+	@Test
+	public void testEncode1() {
+		int[] digits = new int[] { 1, 0, 2 };
+		int n = 5;
+		int l = RewriterAlphabetEncoder.toBaseNNumber(digits, n);
+		assert l == 27;
+	}
+
+}