feat: padded size from height calc function (#18)

src/aggregate.js

@@ -9,7 +9,7 @@ import { indexAreaStart } from './inclusion.js'
 
 const NodeSize = BigInt(Node.Size)
 const EntrySize = Number(Index.EntrySize)
-export const MAX_CAPACITY = 2n ** BigInt(Tree.MAX_HEIGHT) * NodeSize
+export const MAX_CAPACITY = Piece.PaddedSize.fromHeight(Tree.MAX_HEIGHT)
 
 /**
  * Default aggregate size (32GiB).

src/piece.js

@@ -47,7 +47,7 @@ class PieceInfo {
     this.height = height
   }
   get size() {
-    return 2n ** BigInt(this.height) * BigInt(NodeSize)
+    return PaddedSize.fromHeight(this.height)
   }
   toJSON() {
     return toJSON(this)

src/piece/padded-size.js

@@ -58,3 +58,10 @@ export const toUnpaddedSize = (size) => size - size / 128n
  * @param {API.PaddedPieceSize} size
  */
 export const toHeight = (size) => log2Ceil(size / NODE_SIZE)
+
+/**
+ * Calculates the padded size of the piece tree from height.
+ *
+ * @param {number} height
+ */
+export const fromHeight = (height) => 2n ** BigInt(height) * NODE_SIZE

test/piece-size.spec.js

@@ -80,6 +80,22 @@ export const testPieceSize = {
     ])
   ),
 
+  // to height - from height
+  ...Object.fromEntries(
+    [128, 1024, 34359738368].map((size) => [
+      `PaddedSize.fromHeight(PaddedSize.toHeight(PaddedSize.from(${size})))) === ${size}`,
+      (assert) => {
+        assert.equal(
+          PaddedSize.fromHeight(
+            PaddedSize.toHeight(PaddedSize.from(size))
+          ),
+          BigInt(size)
+        )
+      },
+    ])
+  ),
+
+
   // throw
   ...Object.fromEntries(
     [9, 128, 99453687, 1016 + 0x1000000].map((size) => [