first commit

java/expression/Power.java

@@ -0,0 +1,46 @@
+package expression;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+/**
+ * @author Doschennikov Nikita (me@fymio.us)
+ */
+public class Power extends AbstractBinaryOperation {
+    public Power(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 base, int exp) {
+        if (exp < 0) throw new ArithmeticException("negative exponent");
+        if (base == 0 && exp == 0) throw new ArithmeticException("zero to the power of zero");
+        if (exp == 0) return 1;
+        if (base == 0) return 0;
+        int result = 1;
+        int b = base;
+        int e = exp;
+        while (e > 0) {
+            if ((e & 1) == 1) {
+                result = checkedMul(result, b);
+            }
+            if (e > 1) b = checkedMul(b, b);
+            e >>= 1;
+        }
+        return result;
+    }
+
+    private static int checkedMul(int a, int b) {
+        if (a == 0 || b == 0) return 0;
+        if (a == Integer.MIN_VALUE && b == -1) throw new OverflowException("power");
+        if (b == Integer.MIN_VALUE && a == -1) throw new OverflowException("power");
+        int result = a * b;
+        if (result / a != b) throw new OverflowException("power");
+        return result;
+    }
+
+    @Override protected BigInteger applyBi(BigInteger a, BigInteger b) { return a.pow(b.intValueExact()); }
+    @Override protected BigDecimal applyBd(BigDecimal a, BigDecimal b) { return a.pow(b.intValueExact()); }
+}