文字

概述

• Swift的Data（对于64位，暂忽略32位） 的内存布局
  • 根据数据字节个数多少分类
    • count=0
      • empty = 空数据
    • 0 < count < 15 == 0 < count <= 14
      • inline == struct InlineData
        • var bytes: Buffer
          • @usableFromInline typealias Buffer = (UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8) //len //enum
        • var length: UInt8
    • 14 < count < 2^32
      • slice == struct InlineSlice
        • var slice: Range<Int32>
        • var storage: __DataStorage
    • 2^32 <= count < 2^64
      • large == struct LargeSlice
        • var slice: RangeReference
          • var range: Range<Int64>
        • var storage: __DataStorage

__DataStorage

class __DataStorage {
    var isa: objc_class* // NULL for pure Swift class
    var refCount: UInt64
    var _bytes: UnsafeMutableRawPointer?
    var _length: UInt64
    var _capacity: UInt64
    var _offset: UInt64
    var _deallocator: ((UnsafeMutableRawPointer, Int64) -> Void)?
    var _needToZero: Bool
}

==

• class __DataStorage
  • [+0x00] = objc_class* isa
  • [+0x08] = int64 refCount
  • [+0x10] = void* _bytes
  • [+0x18] = int64 _length
  • [+0x20] = int64 _capacity
  • [+0x28] = int64 _offset
  • [+0x30] = function_pointer* _deallocator
    • 函数定义：((UnsafeMutableRawPointer, Int64) -> Void)?
  • [+0x38] = Bool _needToZero

详解

• Swift的Data
  • 分4类
    • 空数据：empty
    • inline == struct InlineData
      • 字段
        • var bytes: Buffer
        • var length: UInt8
      • 说明
        • bytes的Buffer的字节=个数
          • 64位架构：不超过14，即 <=14个字节
            • @usableFromInline typealias Buffer = (UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8, UInt8) //len //enum
          • 32位架构：不超过6，即 <=6个字节
            • @usableFromInline typealias Buffer = (UInt8, UInt8, UInt8, UInt8, UInt8, UInt8) //len //enum
    • slice == struct InlineSlice
      • 字段
        • var slice: Range
        • var storage: __DataStorage
      • 说明
        • InlineData的（64bit的）14个 < InlineSlice的字节个数 < 2^64的最大值？（storage pointer + range == a signle word）
    • large == struct LargeSlice
      • 字段
        • var slice: RangeReference
          • var range: Range
        • var storage: __DataStorage
      • 说明
        • a single word个数=2^64？ < LargeSlice的字节个数 < 双字节大小（two-word size）=2^128？