I performed some micro-benchmarking on my MacBookPro5,3 with respect to
https://bugs.openjdk.java.net/browse/JDK-8029561.
With this patch applied to JDK 9
--- a/src/share/classes/java/lang/Integer.java Tue Dec 24 20:07:12 2013 -0800
+++ b/src/share/classes/java/lang/Integer.java Fri Dec 27 13:45:28 2013 -0800
@@ -453,7 +453,11 @@
// Fall thru to fast mode for smaller numbers
// assert(i <= 65536, i);
for (;;) {
- q = (i * 52429) >>> (16+3);
+ // The value of z1 ends up being 52429*i
+ int z1 = (i << 3) + (i << 2);
+ z1 = (z1 << 4) + z1;
+ z1 = (z1 << 8) + z1 + i;
+ q = z1 >>> 19; // 19 = 16 + 3
r = i - ((q << 3) + (q << 1)); // r = i-(q*10) ...
buf [--charPos] = digits [r];
i = q;
The performance of toString() over 100 random ints in the range [0,0xffff) was
actually about 12% slower than without the patch applied.
Similarly, micro-benchmarks of
int z1 = y*52429
versus
int z1 = (y << 3) + (y << 2);
z1 = (z1 << 4) + z1;
z1 = (z1 << 8) + z1 + y;
showed the latter to be about 8% slower than the former.
The foregoing results suggest that the patch should be rejected and the issue
resolved (as "Won't Fix").
Brian
