first commit

java/expression/Log.java

@@ -0,0 +1,46 @@
+package expression;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class Log extends AbstractBinaryOperation {
+    public Log(AbstractExpression l, AbstractExpression r) { super(l, r); }
+
+    @Override protected String  getOperator()  { return "//"; }
+    @Override protected int     getPriority()  { return 3; }
+    @Override protected boolean isRightAssoc() { return true; }
+
+    @Override
+    protected int applyInt(int a, int b) {
+        if (a <= 0) throw new ArithmeticException("logarithm of non-positive number");
+        if (b <= 1) throw new ArithmeticException("logarithm base must be > 1");
+        int result = 0;
+        int power = 1;
+        while (power <= a / b) {
+            power *= b;
+            result++;
+        }
+        return result;
+    }
+
+    @Override
+    protected BigInteger applyBi(BigInteger a, BigInteger b) {
+        if (a.signum() <= 0) throw new ArithmeticException("logarithm of non-positive number");
+        if (b.compareTo(BigInteger.TWO) < 0) throw new ArithmeticException("logarithm base must be > 1");
+        int result = 0;
+        BigInteger power = BigInteger.ONE;
+        while (power.multiply(b).compareTo(a) <= 0) {
+            power = power.multiply(b);
+            result++;
+        }
+        return BigInteger.valueOf(result);
+    }
+
+    @Override
+    protected BigDecimal applyBd(BigDecimal a, BigDecimal b) {
+        throw new UnsupportedOperationException("log not supported for BigDecimal");
+    }
+}