[GitHub] [lucene] zhaih commented on a diff in pull request #949: LUCENE-10605: fix error in 32bit jvm object alignment gap calculation

[GitBox <gi...@apache.org>]

zhaih commented on code in PR #949:
URL: https://github.com/apache/lucene/pull/949#discussion_r893146609


##########
lucene/core/src/java/org/apache/lucene/util/ArrayUtil.java:
##########
@@ -191,15 +191,17 @@ public static int oversize(int minTargetSize, int bytesPerElement) {
           return newSize;
       }
     } else {
-      // round up to 4 byte alignment in 64bit env
+      // round up to 4 byte alignment in 32bit env

Review Comment:
   this should still be 8 byte alignment, but with 4 bytes offset given by array header, probably it's better to mention in 32 bit machine the array header is 12 bytes so the calculation below become reasonable.



##########
lucene/core/src/java/org/apache/lucene/util/ArrayUtil.java:
##########
@@ -191,15 +191,17 @@ public static int oversize(int minTargetSize, int bytesPerElement) {
           return newSize;
       }
     } else {
-      // round up to 4 byte alignment in 64bit env
+      // round up to 4 byte alignment in 32bit env
       switch (bytesPerElement) {
-        case 2:
-          // round up to multiple of 2
-          return (newSize + 1) & 0x7ffffffe;
         case 1:
-          // round up to multiple of 4
-          return (newSize + 3) & 0x7ffffffc;
+          // round up to multiple of 8 plus 4

Review Comment:
   This is not round "up" strictly speaking since you only round up 5-7 but not 1-4, I'm not sure what's the right words but maybe just say "align with size of 4,12,20..."?



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