# Code review request for 6560935: BigInteger.modPow() throws ArithmeticException for negative exponent

Joseph D. Darcy Joe.Darcy at Sun.COM
Tue Oct 20 21:45:13 UTC 2009

```Hello.

Please review this small doc clarification; modPow is not defined for
negative exponents unless the BigInteger being operated on is relatively
prime to the modulus.  There are a few stylistic javadoc cleanups in the
patch below too.

Webrev:
http://cr.openjdk.java.net/~darcy/6560935.0/

Thanks,

-Joe

--- old/src/share/classes/java/math/BigInteger.java    2009-10-20
14:40:35.000000000 -0700
+++ new/src/share/classes/java/math/BigInteger.java    2009-10-20
14:40:35.000000000 -0700
@@ -478,7 +478,7 @@

/**
* Constructs a randomly generated BigInteger, uniformly
distributed over
-     * the range {@code 0} to (2<sup>{@code numBits}</sup> - 1), inclusive.
+     * the range 0 to (2<sup>{@code numBits}</sup> - 1), inclusive.
* The uniformity of the distribution assumes that a fair source of
random
* bits is provided in {@code rnd}.  Note that this constructor always
* constructs a non-negative BigInteger.
@@ -1332,7 +1332,7 @@
*
* @param  val value by which this BigInteger is to be divided.
* @return {@code this / val}
-     * @throws ArithmeticException {@code val==0}
+     * @throws ArithmeticException if {@code val} is zero.
*/
public BigInteger divide(BigInteger val) {
MutableBigInteger q = new MutableBigInteger(),
@@ -1352,7 +1352,7 @@
* @return an array of two BigIntegers: the quotient {@code (this /
val)}
*         is the initial element, and the remainder {@code (this %
val)}
*         is the final element.
-     * @throws ArithmeticException {@code val==0}
+     * @throws ArithmeticException if {@code val} is zero.
*/
public BigInteger[] divideAndRemainder(BigInteger val) {
BigInteger[] result = new BigInteger[2];
@@ -1371,7 +1371,7 @@
* @param  val value by which this BigInteger is to be divided, and the
*         remainder computed.
* @return {@code this % val}
-     * @throws ArithmeticException {@code val==0}
+     * @throws ArithmeticException if {@code val} is zero.
*/
public BigInteger remainder(BigInteger val) {
MutableBigInteger q = new MutableBigInteger(),
@@ -1547,7 +1547,7 @@
*
* @param  m the modulus.
* @return {@code this mod m}
-     * @throws ArithmeticException {@code m <= 0}
+     * @throws ArithmeticException {@code m} ≤ 0
* @see    #remainder
*/
public BigInteger mod(BigInteger m) {
@@ -1566,7 +1566,9 @@
* @param  exponent the exponent.
* @param  m the modulus.
* @return <tt>this<sup>exponent</sup> mod m</tt>
-     * @throws ArithmeticException {@code m <= 0}
+     * @throws ArithmeticException {@code m} ≤ 0 or the exponent is
+     *         negative and this BigInteger is not <i>relatively
+     *         prime</i> to m.
* @see    #modInverse
*/
public BigInteger modPow(BigInteger exponent, BigInteger m) {
@@ -2015,7 +2017,7 @@
*
* @param  m the modulus.
* @return {@code this}<sup>-1</sup> {@code mod m}.
-     * @throws ArithmeticException {@code  m <= 0}, or this BigInteger
+     * @throws ArithmeticException {@code  m} ≤ 0, or this BigInteger
*         has no multiplicative inverse mod m (that is, this
BigInteger
*         is not <i>relatively prime</i> to m).
*/
@@ -2449,7 +2451,7 @@
/**
* Returns {@code true} if this BigInteger is probably prime,
* {@code false} if it's definitely composite.  If
-     * {@code certainty} is {@code  <= 0}, {@code true} is
+     * {@code certainty} is ≤ 0, {@code true} is
* returned.
*
* @param  certainty a measure of the uncertainty that the caller is

```