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Replace conditional logic in add(), subtract() with bit manipulation #15289

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Replace conditional logic in add(), subtract() with bit manipulation #15289

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18 changes: 6 additions & 12 deletions lucene/core/src/java/org/apache/lucene/util/NumericUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -96,13 +96,10 @@ public static void subtract(int bytesPerDim, int dim, byte[] a, byte[] b, byte[]
int end = start + bytesPerDim;
int borrow = 0;
for (int i = end - 1; i >= start; i--) {
// diff is always in the range [-256, 255]
int diff = (a[i] & 0xff) - (b[i] & 0xff) - borrow;
if (diff < 0) {
diff += 256;
borrow = 1;
} else {
borrow = 0;
}
borrow = (diff >>> 31); // Extract sign bit as borrow
diff += (borrow << 8);
result[i - start] = (byte) diff;
}
if (borrow != 0) {
Expand All @@ -120,12 +117,9 @@ public static void add(int bytesPerDim, int dim, byte[] a, byte[] b, byte[] resu
int carry = 0;
for (int i = end - 1; i >= start; i--) {
int digitSum = (a[i] & 0xff) + (b[i] & 0xff) + carry;
if (digitSum > 255) {
digitSum -= 256;
carry = 1;
} else {
carry = 0;
}
// Below is safe as digitSum can be at most 511(255 * 2 + 1), so never exceeds 9 bits
carry = digitSum >>> 8;
digitSum &= 0xFF;
result[i - start] = (byte) digitSum;
}
if (carry != 0) {
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