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8203352: Improve java implementation of Integer/Long.numberOfLeadingZeros

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Co-authored-by: Ivan Gerasimov <ivan.gerasimov@oracle.com>
Reviewed-by: martin, igerasim
This commit is contained in:
Claes Redestad 2018-05-22 14:44:18 +02:00
parent bff7296db3
commit 55ba3cad8b
4 changed files with 35 additions and 31 deletions
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15
src/java.base/share/classes/java/lang/Integer.java
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@ -1618,16 +1618,15 @@ public final class Integer extends Number implements Comparable<Integer> {
*/
@HotSpotIntrinsicCandidate
public static int numberOfLeadingZeros(int i) {
// HD, Figure 5-6
// HD, Count leading 0's
if (i <= 0)
return i == 0 ? 32 : 0;
int n = 1;
if (i >>> 16 == 0) { n += 16; i <<= 16; }
if (i >>> 24 == 0) { n += 8; i <<= 8; }
if (i >>> 28 == 0) { n += 4; i <<= 4; }
if (i >>> 30 == 0) { n += 2; i <<= 2; }
n -= i >>> 31;
return n;
int n = 31;
if (i >= 1 << 16) { n -= 16; i >>>= 16; }
if (i >= 1 << 8) { n -= 8; i >>>= 8; }
if (i >= 1 << 4) { n -= 4; i >>>= 4; }
if (i >= 1 << 2) { n -= 2; i >>>= 2; }
return n - (i >>> 1);
}
/**