Re: BitSet vs BigInteger (false Android doc)

From:

Jan Burse <janburse@fastmail.fm>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 03 Sep 2011 20:15:02 +0200

Message-ID:

<j3tqr7$vp8$1@news.albasani.net>

Patricia Shanahan schrieb:

On 9/2/2011 1:51 PM, Jan Burse wrote:

Patricia Shanahan schrieb:

Also, they have more freedom of action in implementing BitSet

True, actually I was expecting to see a more clever BitSet,
but in JDK 1.6.0_26 its just this long array.

Are you looking at the actual Android implementations for the classes?

Patricia

I don't think that Android uses some special BitSet resp. BigInteger,
since then classes are java.*.

But it looks that nevertheless the implementation in JDK and Android are
not verbatim the same:

Here is the Android BitSet XOR:

             public void xor(BitSet bs) {
                 int bsActualLen = bs.getActualArrayLength();
                 if (bsActualLen > bits.length) {
                     long[] tempBits = new long[bsActualLen];
                     System.arraycopy(bs.bits, 0, tempBits, 0,
                             bs.actualArrayLength);
                     for (int i = 0; i < actualArrayLength; i++) {
                         tempBits[i] ^= bits[i];
                     }
                     bits = tempBits;
                     actualArrayLength = bsActualLen;
                     isLengthActual = !((actualArrayLength > 0) &&
(bits[actualArrayLength - 1] == 0));
                 } else {
                     long[] bsBits = bs.bits;
                     for (int i = 0; i < bsActualLen; i++) {
                         bits[i] ^= bsBits[i];
                     }
                     if (bsActualLen > actualArrayLength) {
                         actualArrayLength = bsActualLen;
                         isLengthActual = true;
                     }
                 }
                 needClear();
             }

    http://www.java2s.com/Open-Source/Android/android-core/platform-libcore/java/util/BitSet.java.htm

And here is the Oracle JDK BitSet XOR:

     public void xor(BitSet set) {
         int wordsInCommon = Math.min(wordsInUse, set.wordsInUse);

         if (wordsInUse < set.wordsInUse) {
             ensureCapacity(set.wordsInUse);
             wordsInUse = set.wordsInUse;
         }

     // Perform logical XOR on words in common
         for (int i = 0; i < wordsInCommon; i++)
         words[i] ^= set.words[i];

     // Copy any remaining words
     if (wordsInCommon < set.wordsInUse)
         System.arraycopy(set.words, wordsInCommon,
                  words, wordsInCommon,
                  set.wordsInUse - wordsInCommon);

         recalculateWordsInUse();
     checkInvariants();
     }

So basically the same representation and algorithm.
The Android seems to stem from Apache Harmony.

http://en.wikipedia.org/wiki/Apache_Harmony#Use_in_Android_SDK

Bye

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