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4891331: BigInteger a.multiply(a) should use squaring code

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Change multiply(BigInteger a) to return square() if a == this and the number of ints in the magnitude is over a threshold.

Reviewed-by: darcy, shade
This commit is contained in:
Brian Burkhalter 2013-12-13 16:15:58 -08:00
parent 73f4f12f6a
commit 997e4bbc8b
1 changed files with 17 additions and 1 deletions
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18
jdk/src/share/classes/java/math/BigInteger.java
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@ -268,7 +268,15 @@ public class BigInteger extends Number implements Comparable<BigInteger> {
*/
private static final int SCHOENHAGE_BASE_CONVERSION_THRESHOLD = 20;
//Constructors
/**
* The threshold value for using squaring code to perform multiplication
* of a {@code BigInteger} instance by itself. If the number of ints in
* the number are larger than this value, {@code multiply(this)} will
* return {@code square()}.
*/
private static final int MULTIPLY_SQUARE_THRESHOLD = 20;
// Constructors
/**
* Translates a byte array containing the two's-complement binary
@ -1458,6 +1466,9 @@ public class BigInteger extends Number implements Comparable<BigInteger> {
/**
* Returns a BigInteger whose value is {@code (this * val)}.
*
* @implNote An implementation may offer better algorithmic
* performance when {@code val == this}.
*
* @param val value to be multiplied by this BigInteger.
* @return {@code this * val}
*/
@ -1466,6 +1477,11 @@ public class BigInteger extends Number implements Comparable<BigInteger> {
return ZERO;
int xlen = mag.length;
if (val == this && xlen > MULTIPLY_SQUARE_THRESHOLD) {
return square();
}
int ylen = val.mag.length;
if ((xlen < KARATSUBA_THRESHOLD) || (ylen < KARATSUBA_THRESHOLD)) {