Add java.lang.Utils.roundUpToPowerOfTwo utility function

tanishiking · tanishiking · commit 94acdf8cbf04 · 2025-07-19T23:44:49.000+09:00
The use-case of this function is for ensuring the size of internal buffers (e.g. internal Array of `ju.ArrayList`).
diff --git a/javalib/src/main/scala/java/lang/Utils.scala b/javalib/src/main/scala/java/lang/Utils.scala
@@ -187,4 +187,9 @@ private[java] object Utils {
     false
     // scalastyle:on return
   }
+
+  /** Round up to a power of 2; if overflow, returns the given number. */
+  @inline def roundUpToPowerOfTwo(i: Int): Int =
+    if (i > (1 << 30)) i
+    else ((1 << 31) >>> (Integer.numberOfLeadingZeros(i - 1)) - 1)
 }
diff --git a/javalib/src/main/scala/java/util/ArrayList.scala b/javalib/src/main/scala/java/util/ArrayList.scala
@@ -66,12 +66,8 @@ class ArrayList[E] private (innerInit: AnyRef, private var _size: Int)
 
   def ensureCapacity(minCapacity: Int): Unit = {
     if (isWebAssembly) {
-      if (innerWasm.length < minCapacity) {
-        if (minCapacity > (1 << 30))
-          resizeTo(minCapacity)
-        else
-          resizeTo(((1 << 31) >>> (Integer.numberOfLeadingZeros(minCapacity - 1)) - 1))
-      }
+      if (innerWasm.length < minCapacity)
+        resizeTo(roundUpToPowerOfTwo(minCapacity))
     }
     // We ignore this in JS as js.Array doesn't support explicit pre-allocation
   }

Original file line number	Diff line number	Diff line change
`@@ -187,4 +187,9 @@ private[java] object Utils {`
`187`	`187`	`false`
`188`	`188`	`// scalastyle:on return`
`189`	`189`	`}`
	`190`	`+`
	`191`	`+ /** Round up to a power of 2; if overflow, returns the given number. */`
	`192`	`+ @inline def roundUpToPowerOfTwo(i: Int): Int =`
	`193`	`+ if (i > (1 << 30)) i`
	`194`	`+ else ((1 << 31) >>> (Integer.numberOfLeadingZeros(i - 1)) - 1)`
`190`	`195`	`}`
Original file line number	Diff line number	Diff line change
`@@ -66,12 +66,8 @@ class ArrayList[E] private (innerInit: AnyRef, private var _size: Int)`
`66`	`66`
`67`	`67`	`def ensureCapacity(minCapacity: Int): Unit = {`
`68`	`68`	`if (isWebAssembly) {`
`69`		`- if (innerWasm.length < minCapacity) {`
`70`		`- if (minCapacity > (1 << 30))`
`71`		`- resizeTo(minCapacity)`
`72`		`- else`
`73`		`- resizeTo(((1 << 31) >>> (Integer.numberOfLeadingZeros(minCapacity - 1)) - 1))`
`74`		`- }`
	`69`	`+ if (innerWasm.length < minCapacity)`
	`70`	`+ resizeTo(roundUpToPowerOfTwo(minCapacity))`
`75`	`71`	`}`
`76`	`72`	`// We ignore this in JS as js.Array doesn't support explicit pre-allocation`
`77`	`73`	`}`