Imposed a limit on the power() exponent

Just discovered that bcpow() on HHVM has a weird exponent limit of 2^27+1 (empirically determined), after which it triggers an "exponent too large in raise" error.
Anyway, an exponent of 1,000,000 is more than reasonable for most, if not all, use cases.

src/BigDecimal.php

@@ -288,7 +288,9 @@ class BigDecimal implements \Serializable
     /**
      * Returns this number exponentiated.
      *
-     * @param integer $exponent The exponent, as a positive-or-zero integer.
+     * The exponent has a limit of 1 million.
+     *
+     * @param integer $exponent The exponent, between 0 and 1,000,000.
      *
      * @return BigDecimal
      */
@@ -296,8 +298,12 @@ class BigDecimal implements \Serializable
     {
         $exponent = (int) $exponent;
 
-        if ($exponent < 0) {
-            throw new \InvalidArgumentException('The exponent cannot be negative.');
+        if ($exponent < 0 || $exponent > Calculator::MAX_POWER) {
+            throw new \InvalidArgumentException(sprintf(
+                'The exponent %d is not in the range 0 to %d.',
+                $exponent,
+                Calculator::MAX_POWER
+            ));
         }
 
         return new BigDecimal(Calculator::get()->pow($this->value, $exponent), $this->scale * $exponent);

src/Internal/Calculator.php

@@ -17,6 +17,11 @@ use Brick\Math\RoundingMode;
  */
 abstract class Calculator
 {
+    /**
+     * The maximum exponent value allowed for the pow() method.
+     */
+    const MAX_POWER = 1000000;
+
     /**
      * The Calculator instance in use.
      *
@@ -265,7 +270,7 @@ abstract class Calculator
      * Exponentiates a number.
      *
      * @param string  $a The base.
-     * @param integer $e The exponent, must be a positive-or-zero integer.
+     * @param integer $e The exponent, validated as an integer between 0 and MAX_POWER.
      *
      * @return string The power.
      */

tests/BigDecimalTest.php

@@ -1191,8 +1191,8 @@ abstract class BigDecimalTest extends AbstractTestCase
             ['2',  3,   '8', 0],
             ['3',  3,  '27', 0],
 
-            ['0', 1000000000, '0', 0],
-            ['1', 1000000000, '1', 0],
+            ['0', 1000000, '0', 0],
+            ['1', 1000000, '1', 0],
 
             ['-2', 255, '-57896044618658097711785492504343953926634992332820282019728792003956564819968', 0],
             [ '2', 256, '115792089237316195423570985008687907853269984665640564039457584007913129639936', 0],
@@ -1206,11 +1206,25 @@ abstract class BigDecimalTest extends AbstractTestCase
     }
 
     /**
+     * @dataProvider providerPowerWithInvalidExponentThrowsException
      * @expectedException \InvalidArgumentException
+     *
+     * @param integer $power
      */
-    public function testPowerWithNegativeExponentThrowsException()
+    public function testPowerWithInvalidExponentThrowsException($power)
     {
-        BigDecimal::of(10)->power(-1);
+        BigDecimal::of(1)->power($power);
+    }
+
+    /**
+     * @return array
+     */
+    public function providerPowerWithInvalidExponentThrowsException()
+    {
+        return [
+            [-1],
+            [1000001]
+        ];
     }
 
     /**