8209171: Simplify Java implementation of Integer/Long.numberOfTrailingZeros()
Reviewed-by: martin
Contributed-by: ivan.gerasimov@oracle.com, martinrb@google.com
--- a/src/java.base/share/classes/java/lang/Integer.java Thu Aug 23 09:36:13 2018 -0700
+++ b/src/java.base/share/classes/java/lang/Integer.java Thu Aug 23 12:09:46 2018 -0700
@@ -1654,15 +1654,15 @@
*/
@HotSpotIntrinsicCandidate
public static int numberOfTrailingZeros(int i) {
- // HD, Figure 5-14
- int y;
- if (i == 0) return 32;
- int n = 31;
- y = i <<16; if (y != 0) { n = n -16; i = y; }
- y = i << 8; if (y != 0) { n = n - 8; i = y; }
- y = i << 4; if (y != 0) { n = n - 4; i = y; }
- y = i << 2; if (y != 0) { n = n - 2; i = y; }
- return n - ((i << 1) >>> 31);
+ // HD, Count trailing 0's
+ i = ~i & (i - 1);
+ if (i <= 0) return i & 32;
+ int n = 1;
+ 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);
}
/**
--- a/src/java.base/share/classes/java/lang/Long.java Thu Aug 23 09:36:13 2018 -0700
+++ b/src/java.base/share/classes/java/lang/Long.java Thu Aug 23 12:09:46 2018 -0700
@@ -1782,16 +1782,9 @@
*/
@HotSpotIntrinsicCandidate
public static int numberOfTrailingZeros(long i) {
- // HD, Figure 5-14
- int x, y;
- if (i == 0) return 64;
- int n = 63;
- y = (int)i; if (y != 0) { n = n -32; x = y; } else x = (int)(i>>>32);
- y = x <<16; if (y != 0) { n = n -16; x = y; }
- y = x << 8; if (y != 0) { n = n - 8; x = y; }
- y = x << 4; if (y != 0) { n = n - 4; x = y; }
- y = x << 2; if (y != 0) { n = n - 2; x = y; }
- return n - ((x << 1) >>> 31);
+ int x = (int)i;
+ return x == 0 ? 32 + Integer.numberOfTrailingZeros((int)(i >>> 32))
+ : Integer.numberOfTrailingZeros(x);
}
/**