OpenJDK / jdk8u / jdk8u / jdk
changeset 9125:4f07e4b5bf7d
4891331: BigInteger a.multiply(a) should use squaring code
Summary: 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, coffeys
| author | bpb |
|---|---|
| date | Wed, 05 Feb 2014 15:02:59 -0800 |
| parents | 20620baf438e |
| children | 6c587189a483 |
| files | src/share/classes/java/math/BigInteger.java |
| diffstat | 1 files changed, 17 insertions(+), 1 deletions(-) [+] |
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--- a/src/share/classes/java/math/BigInteger.java Tue Feb 04 18:45:20 2014 -0800 +++ b/src/share/classes/java/math/BigInteger.java Wed Feb 05 15:02:59 2014 -0800 @@ -268,7 +268,15 @@ */ 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 @@ /** * 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 @@ 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)) {