HADOOP-14313. Replace/improve Hadoop's byte[] comparator. Contributed by Vikas Vishwakarma.
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@ -196,6 +196,14 @@ by Google Inc, which can be obtained at:
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* HOMEPAGE:
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* http://code.google.com/p/snappy/
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This product contains a modified portion of UnsignedBytes LexicographicalComparator
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from Guava v21 project by Google Inc, which can be obtained at:
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* LICENSE:
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* license/COPYING (Apache License 2.0)
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* HOMEPAGE:
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* https://github.com/google/guava
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This product optionally depends on 'JBoss Marshalling', an alternative Java
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serialization API, which can be obtained at:
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@ -26,7 +26,6 @@
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import org.slf4j.LoggerFactory;
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import sun.misc.Unsafe;
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import com.google.common.primitives.Longs;
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import com.google.common.primitives.UnsignedBytes;
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/**
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@ -195,52 +194,43 @@ public int compareTo(byte[] buffer1, int offset1, int length1,
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length1 == length2) {
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return 0;
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}
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final int stride = 8;
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int minLength = Math.min(length1, length2);
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int minWords = minLength / Longs.BYTES;
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int strideLimit = minLength & ~(stride - 1);
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int offset1Adj = offset1 + BYTE_ARRAY_BASE_OFFSET;
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int offset2Adj = offset2 + BYTE_ARRAY_BASE_OFFSET;
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int i;
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/*
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* Compare 8 bytes at a time. Benchmarking shows comparing 8 bytes at a
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* time is no slower than comparing 4 bytes at a time even on 32-bit.
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* On the other hand, it is substantially faster on 64-bit.
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*/
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for (int i = 0; i < minWords * Longs.BYTES; i += Longs.BYTES) {
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for (i = 0; i < strideLimit; i += stride) {
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long lw = theUnsafe.getLong(buffer1, offset1Adj + (long) i);
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long rw = theUnsafe.getLong(buffer2, offset2Adj + (long) i);
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long diff = lw ^ rw;
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if (diff != 0) {
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if (lw != rw) {
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if (!littleEndian) {
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return lessThanUnsigned(lw, rw) ? -1 : 1;
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}
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// Use binary search
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int n = 0;
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int y;
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int x = (int) diff;
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if (x == 0) {
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x = (int) (diff >>> 32);
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n = 32;
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}
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y = x << 16;
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if (y == 0) {
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n += 16;
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} else {
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x = y;
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}
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y = x << 8;
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if (y == 0) {
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n += 8;
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}
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return (int) (((lw >>> n) & 0xFFL) - ((rw >>> n) & 0xFFL));
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/*
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* We want to compare only the first index where left[index] !=
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* right[index]. This corresponds to the least significant nonzero
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* byte in lw ^ rw, since lw and rw are little-endian.
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* Long.numberOfTrailingZeros(diff) tells us the least significant
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* nonzero bit, and zeroing out the first three bits of L.nTZ gives
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* us the shift to get that least significant nonzero byte. This
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* comparison logic is based on UnsignedBytes from Guava v21
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*/
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int n = Long.numberOfTrailingZeros(lw ^ rw) & ~0x7;
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return ((int) ((lw >>> n) & 0xFF)) - ((int) ((rw >>> n) & 0xFF));
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}
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}
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// The epilogue to cover the last (minLength % 8) elements.
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for (int i = minWords * Longs.BYTES; i < minLength; i++) {
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for (; i < minLength; i++) {
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int result = UnsignedBytes.compare(
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buffer1[offset1 + i],
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buffer2[offset2 + i]);
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