plus32:

diff -r 1e5cc55ae5d3 src/java.base/share/classes/java/lang/AbstractStringBuilder.java
--- a/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Thu Apr 23 18:01:01 2015 +0800
+++ b/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Fri Apr 24 17:36:19 2015 +0300
@@ -129,9 +129,10 @@
      * size check or synchronization.
      */
     void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2 + 2;
+        int newCapacity = value.length * 2;
         if (newCapacity - minimumCapacity < 0)
             newCapacity = minimumCapacity;
+        newCapacity += 32; // additional capacity, anticipating follow-up ops
         if (newCapacity < 0) {
             if (minimumCapacity < 0) // overflow
                 throw new OutOfMemoryError();

mult2:

--- a/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Thu Apr 23 18:01:01 2015 +0800
+++ b/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Fri Apr 24 17:51:32 2015 +0300
@@ -130,8 +130,8 @@
      */
     void expandCapacity(int minimumCapacity) {
         int newCapacity = value.length * 2 + 2;
-        if (newCapacity - minimumCapacity < 0)
-            newCapacity = minimumCapacity;
+        while (newCapacity - minimumCapacity < 0)
+            newCapacity = newCapacity * 2;
         if (newCapacity < 0) {
             if (minimumCapacity < 0) // overflow
                 throw new OutOfMemoryError();



mult2-plus32:

diff -r 1e5cc55ae5d3 src/java.base/share/classes/java/lang/AbstractStringBuilder.java
--- a/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Thu Apr 23 18:01:01 2015 +0800
+++ b/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Fri Apr 24 17:39:39 2015 +0300
@@ -129,9 +129,10 @@
      * size check or synchronization.
      */
     void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2 + 2;
-        if (newCapacity - minimumCapacity < 0)
-            newCapacity = minimumCapacity;
+        int newCapacity = value.length * 2;
+        while (newCapacity - minimumCapacity < 0)
+            newCapacity = newCapacity * 2;
+        newCapacity += 32; // additional capacity, anticipating follow-up ops
         if (newCapacity < 0) {
             if (minimumCapacity < 0) // overflow
                 throw new OutOfMemoryError();

plus32-round8:

diff -r 1e5cc55ae5d3 src/java.base/share/classes/java/lang/AbstractStringBuilder.java
--- a/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Thu Apr 23 18:01:01 2015 +0800
+++ b/src/java.base/share/classes/java/lang/AbstractStringBuilder.java	Tue May 05 11:22:22 2015 +0300
@@ -129,9 +125,13 @@
      * size check or synchronization.
      */
     void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2 + 2;
+        int newCapacity = value.length * 2;
         if (newCapacity - minimumCapacity < 0)
             newCapacity = minimumCapacity;
+
+        // Expect follow-up ops: add a padding.
+        // It is also nicer to array copy to make the storage round.
+        newCapacity = (newCapacity + 32) & ~8;
         if (newCapacity < 0) {
             if (minimumCapacity < 0) // overflow
                 throw new OutOfMemoryError();