[Swift] Moves capacity outside of Storage (#8650)

- Cleans up capacity usage within the lib and moves it outside of the Storage

-  Use overflow operators

swift/Sources/FlexBuffers/ByteBuffer.swift

@@ -40,11 +40,11 @@ public struct ByteBuffer {
 
     /// This storage doesn't own the memory, therefore, we won't deallocate on deinit.
     private let isOwned: Bool
+    /// Capacity of UInt8 the buffer can hold
+    private let capacity: Int
     /// Retained blob of data that requires the storage to retain a pointer to.
     @usableFromInline
     var retainedBlob: Blob
-    /// Capacity of UInt8 the buffer can hold
-    var capacity: Int
 
     @usableFromInline
     init(count: Int) {
@@ -178,12 +178,10 @@ public struct ByteBuffer {
 
   /// The size of the elements written to the buffer + their paddings
   private var _readerIndex: Int = 0
-//  /// Reader is the position of the current Writer Index (capacity - size)
-//  var reader: Int { _storage.capacity &- _readerIndex }
   /// Current size of the buffer
   public var count: Int { _readerIndex }
   /// Current capacity for the buffer including unused space
-  public var capacity: Int { _storage.capacity }
+  public let capacity: Int
 
   /// Constructor that creates a Flatbuffer object from an InternalByteBuffer
   /// - Parameter
@@ -194,6 +192,7 @@ public struct ByteBuffer {
       blob: .byteBuffer(byteBuffer),
       capacity: byteBuffer.capacity)
     _readerIndex = byteBuffer.writerIndex
+    capacity = byteBuffer.capacity
   }
 
   /// Constructor that creates a Flatbuffer from unsafe memory region by copying
@@ -209,7 +208,8 @@ public struct ByteBuffer {
   {
     _storage = Storage(count: capacity)
     _storage.copy(from: memory, count: capacity)
-    _readerIndex = _storage.capacity
+    _readerIndex = capacity
+    self.capacity = capacity
   }
 
   /// Constructor that creates a Flatbuffer object from a UInt8
@@ -218,7 +218,8 @@ public struct ByteBuffer {
   @inline(__always)
   public init(bytes: [UInt8]) {
     _storage = Storage(blob: .array(bytes), capacity: bytes.count)
-    _readerIndex = _storage.capacity
+    _readerIndex = bytes.count
+    capacity = bytes.count
   }
 
   #if !os(WASI)
@@ -228,7 +229,8 @@ public struct ByteBuffer {
   @inline(__always)
   public init(data: Data) {
     _storage = Storage(blob: .data(data), capacity: data.count)
-    _readerIndex = _storage.capacity
+    _readerIndex = data.count
+    capacity = data.count
   }
 
   /// Constructor that creates a Flatbuffer object from a ContiguousBytes
@@ -241,7 +243,8 @@ public struct ByteBuffer {
     count: Int)
   {
     _storage = Storage(blob: .bytes(contiguousBytes), capacity: count)
-    _readerIndex = _storage.capacity
+    _readerIndex = count
+    capacity = count
   }
   #endif
 
@@ -259,7 +262,8 @@ public struct ByteBuffer {
     _storage = Storage(
       blob: .pointer(memory),
       capacity: capacity)
-    _readerIndex = _storage.capacity
+    _readerIndex = capacity
+    self.capacity = capacity
   }
 
   /// Creates a copy of the existing flatbuffer, by copying it to a different memory.
@@ -275,6 +279,7 @@ public struct ByteBuffer {
   {
     _storage = Storage(blob: blob, capacity: count)
     _readerIndex = removeBytes
+    capacity = count
   }
 
   /// Write stores an object into the buffer directly or indirectly.
@@ -289,11 +294,11 @@ public struct ByteBuffer {
   func write<T>(value: T, index: Int, direct: Bool = false) {
     var index = index
     if !direct {
-      index = _storage.capacity &- index
+      index = capacity &- index
     }
-    assert(index < _storage.capacity, "Write index is out of writing bound")
+    assert(index < capacity, "Write index is out of writing bound")
     assert(index >= 0, "Writer index should be above zero")
-    withUnsafePointer(to: value) { ptr in
+    _ = withUnsafePointer(to: value) { ptr in
       _storage.withUnsafeRawPointer {
         memcpy(
           $0.advanced(by: index),
@@ -387,7 +392,7 @@ public struct ByteBuffer {
     count: Int) -> [T]
   {
     assert(
-      index + count <= _storage.capacity,
+      index + count <= capacity,
       "Reading out of bounds is illegal")
 
     return _storage.readWithUnsafeRawPointer(position: index) {
@@ -405,7 +410,7 @@ public struct ByteBuffer {
     type: String.Encoding) -> String?
   {
     assert(
-      index + count <= _storage.capacity,
+      index + count <= capacity,
       "Reading out of bounds is illegal")
     return _storage.readWithUnsafeRawPointer(position: index) {
       let buf = UnsafeBufferPointer(
@@ -427,7 +432,7 @@ public struct ByteBuffer {
     count: Int) -> String?
   {
     assert(
-      index + count <= _storage.capacity,
+      index + count <= capacity,
       "Reading out of bounds is illegal")
     return _storage.readWithUnsafeRawPointer(position: index) {
       String(cString: $0.bindMemory(to: UInt8.self, capacity: count))
@@ -446,7 +451,7 @@ public struct ByteBuffer {
     body: (UnsafeRawBufferPointer) throws -> T) rethrows -> T
   {
     assert(
-      index + count <= _storage.capacity,
+      index + count <= capacity,
       "Reading out of bounds is illegal")
     return try _storage.readWithUnsafeRawPointer(position: index) {
       try body(UnsafeRawBufferPointer(start: $0, count: count))

swift/Sources/FlexBuffers/Reader/FlexBufferVector.swift

@@ -25,7 +25,7 @@ extension FlexBufferVector {
     json += "["
     for i in 0..<count {
       if let val = self[i]?.jsonString() {
-        let comma = i == count - 1 ? "" : ", "
+        let comma = i == count &- 1 ? "" : ", "
         json += "\(val)\(comma)"
       }
     }

swift/Sources/FlexBuffers/Reader/Map.swift

@@ -52,7 +52,7 @@ extension Map {
     json += "{"
     for i in 0..<count {
       if let key = keys[i]?.cString {
-        let comma = i == count - 1 ? "" : ", "
+        let comma = i == count &- 1 ? "" : ", "
         let value = values[i]?.jsonString() ?? StaticJSON.null
         json += "\"\(key)\": \(value)\(comma)"
       }

swift/Sources/FlexBuffers/Utils/functions.swift

@@ -117,9 +117,9 @@ func toFixedTypedVectorElementType(type: FlexBufferType)
   let fixedType: UInt64 = numericCast(
     type.rawValue &- FlexBufferType.vectorInt2
       .rawValue)
-  let len: Int = numericCast((fixedType / 3) + 2)
+  let len: Int = numericCast(fixedType.dividedReportingOverflow(by: 3).partialValue &+ 2)
   return (
-    FlexBufferType(rawValue: (fixedType % 3) + FlexBufferType.int.rawValue),
+    FlexBufferType(rawValue: (fixedType.quotientAndRemainder(dividingBy: 3).remainder) &+ FlexBufferType.int.rawValue),
     len)
 }
 

swift/Sources/FlexBuffers/Writer/FlexBuffersWriter.swift

@@ -143,7 +143,7 @@ public struct FlexBuffersWriter {
   {
     let vec = createVector(
       start: start,
-      count: stack.count - start,
+      count: stack.count &- start,
       step: 1,
       typed: typed,
       fixed: fixed,
@@ -211,7 +211,7 @@ public struct FlexBuffersWriter {
       typed: true,
       fixed: false)
     let vec = createVector(
-      start: start + 1,
+      start: start &+ 1,
       count: len,
       step: 2,
       typed: false,
@@ -598,7 +598,7 @@ public struct FlexBuffersWriter {
 
     var sloc: UInt = numericCast(writerIndex)
     key.withCString {
-      _bb.writeBytes($0, len: len + 1)
+      _bb.writeBytes($0, len: len &+ 1)
     }
 
     if flags > .shareKeys {
@@ -705,7 +705,7 @@ public struct FlexBuffersWriter {
       /// If this vector is part of a map, we will pre-fix an offset to the keys
       /// to this vector.
       bitWidth = max(bitWidth, keys!.elementWidth(size: writerIndex, index: 0))
-      prefixElements += 2
+      prefixElements = prefixElements &+ 2
     }
     var vectorType: FlexBufferType = .key
 

swift/Sources/FlexBuffers/_InternalByteBuffer.swift

@@ -32,32 +32,18 @@ struct _InternalByteBuffer {
   final class Storage {
     /// pointer to the start of the buffer object in memory
     var memory: UnsafeMutableRawPointer
-    /// Capacity of UInt8 the buffer can hold
-    var capacity: Int
 
     @usableFromInline
     init(count: Int, alignment: Int) {
       memory = UnsafeMutableRawPointer.allocate(
         byteCount: count,
         alignment: alignment)
-      capacity = count
-    }
-
-    @usableFromInline
-    init(memory: UnsafeMutableRawPointer, capacity: Int, unowned: Bool) {
-      self.memory = memory
-      self.capacity = capacity
     }
 
     deinit {
       memory.deallocate()
     }
 
-    @usableFromInline
-    func copy(from ptr: UnsafeRawPointer, count: Int) {
-      memory.copyMemory(from: ptr, byteCount: count)
-    }
-
     @usableFromInline
     func initialize(for size: Int) {
       memset(memory, 0, size)
@@ -66,14 +52,11 @@ struct _InternalByteBuffer {
     /// Reallocates the buffer incase the object to be written doesnt fit in the current buffer
     /// - Parameter size: Size of the current object
     @usableFromInline
-    func reallocate(_ size: Int, writerSize: Int, alignment: Int) {
-      while capacity <= writerSize &+ size {
-        capacity = capacity << 1
-      }
-
-      /// solution take from Apple-NIO
-      capacity = capacity.convertToPowerofTwo
-
+    func reallocate(
+      capacity: Int,
+      writerSize: Int,
+      alignment: Int
+    ) {
       let newData = UnsafeMutableRawPointer.allocate(
         byteCount: capacity,
         alignment: alignment)
@@ -97,7 +80,7 @@ struct _InternalByteBuffer {
   /// Public Pointer to the buffer object in memory. This should NOT be modified for any reason
   public var memory: UnsafeMutableRawPointer { _storage.memory }
   /// Current capacity for the buffer
-  public var capacity: Int { _storage.capacity }
+  public private(set) var capacity: Int
 
   /// Returns the written bytes into the ``ByteBuffer``
   public var underlyingBytes: [UInt8] {
@@ -113,6 +96,7 @@ struct _InternalByteBuffer {
   ///   - allowReadingUnalignedBuffers: allow reading from unaligned buffer
   init(initialSize size: Int) {
     initialSize = size.convertToPowerofTwo
+    capacity = initialSize
     _storage = Storage(count: initialSize, alignment: alignment)
     _storage.initialize(for: initialSize)
   }
@@ -123,8 +107,9 @@ struct _InternalByteBuffer {
     writerIndex = 0
     alignment = 1
     if keepingCapacity {
-      _storage.initialize(for: _storage.capacity)
+      _storage.initialize(for: capacity)
     } else {
+      capacity = initialSize
       _storage = Storage(count: initialSize, alignment: alignment)
     }
   }
@@ -136,10 +121,22 @@ struct _InternalByteBuffer {
 
   /// Makes sure that buffer has enouch space for each of the objects that will be written into it
   /// - Parameter size: size of object
-  @inline(__always)
+  @usableFromInline
   mutating func ensureSpace(size: Int) {
-    guard size &+ writerIndex > _storage.capacity else { return }
-    _storage.reallocate(size, writerSize: writerIndex, alignment: alignment)
+    guard size &+ writerIndex > capacity else { return }
+    
+    while capacity <= writerIndex &+ size {
+      capacity = capacity << 1
+    }
+
+    /// solution take from Apple-NIO
+    capacity = capacity.convertToPowerofTwo
+
+    _storage.reallocate(
+      capacity: capacity,
+      writerSize: writerIndex,
+      alignment: alignment
+    )
   }
 
   @inline(__always)
@@ -215,7 +212,7 @@ extension _InternalByteBuffer: CustomDebugStringConvertible {
 
   public var debugDescription: String {
     """
-    buffer located at: \(_storage.memory), with capacity of \(_storage.capacity)
+    buffer located at: \(_storage.memory), with capacity of \(capacity)
     { writerIndex: \(writerIndex) }
     """
   }