如何将 swift 中的字节转换为浮点值?
How to convert bytes to a float value in swift?
这是我将字节数据转换为浮点数的代码。我尝试了本网站给出的所有答案。我得到这个“<44fa0000>”字节数据的指数值
static func returnFloatValue(mutableData:NSMutableData)->Float
{
let qtyRange = mutableData.subdataWithRange(NSMakeRange(0, 4))
let qtyString = String(qtyRange)
let qtyTrimString = qtyString.stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "<>"))
let qtyValue = Float(strtoul(qtyTrimString, nil, 16)/10)
return qtyValue
}
谢谢
使用这个函数:
static func returnFloatValue(data: NSMutableData) -> Float {
let bytes = [UInt8](data as Data)
var f: Float = 0
memcpy(&f, bytes, 4)
return f
}
你可以在这里看到它的实际效果:
var initialValue: Float = 19.200
let data = NSMutableData(bytes: &initialValue, length: 4)
func returnFloatValue(data: NSMutableData) -> Float {
let bytes = [UInt8](data as Data)
var f: Float = 0
memcpy(&f, bytes, 4)
return f
}
var result:Float = returnFloatValue(data: data)
print("f=\(result)")// f=19.2
<44fa0000>
是 big-endian 内存表示
二进制浮点数 2000.0
。从中取回号码
数据,你必须首先将它读入 UInt32
,从
big-endian 托管字节顺序,然后将结果转换为
Float
.
在Swift 2中就是
func floatValueFromData(data: NSData) -> Float {
return unsafeBitCast(UInt32(bigEndian: UnsafePointer(data.bytes).memory), Float.self)
}
示例:
let bytes: [UInt8] = [0x44, 0xFA, 0x00, 0x00]
let data = NSData(bytes: bytes, length: 4)
print(data) // <44fa0000>
let f = floatValueFromData(data)
print(f) // 2000.0
在 Swift 3 中,您将使用 Data
而不是 NSData
,并且
unsafeBitCast
可以替换为 Float(bitPattern:)
初始值设定项:
func floatValue(data: Data) -> Float {
return Float(bitPattern: UInt32(bigEndian: data.withUnsafeBytes { [=12=].pointee } ))
}
在 Swift 5 中,Data
的 withUnsafeBytes()
方法使用(未类型化的)UnsafeRawBufferPointer
调用闭包,并且您可以 load()
来自原始内存的值:
func floatValue(data: Data) -> Float {
return Float(bitPattern: UInt32(bigEndian: data.withUnsafeBytes { [=13=].load(as: UInt32.self) }))
}
这是一些 swift 5:
let data = Data([0x44, 0xfa, 0x00, 0x00]) // 0x44fa0000
let floatNb:Float = data.withUnsafeBytes { [=10=].load(as: Float.self) }
// note that depending on the input endianess, you could add .reversed() to data
let floatNb:Float = data.reversed().withUnsafeBytes { [=10=].load(as: Float.self) }
警告:如果您的数据小于 4 个字节,此示例将抛出。
.
安全数据扩展:
extension Data {
enum Endianess {
case little
case big
}
func toFloat(endianess: Endianess = .little) -> Float? {
guard self.count <= 4 else { return nil }
switch endianess {
case .big:
let data = [UInt8](repeating: 0x00, count: 4-self.count) + self
return data.withUnsafeBytes { [=11=].load(as: Float.self) }
case .little:
let data = self + [UInt8](repeating: 0x00, count: 4-self.count)
return data.reversed().withUnsafeBytes { [=11=].load(as: Float.self) }
}
}
}
测试:
let opData = Data([0x44, 0xFA, 0x00, 0x00])
let nb42 = Data([0x42, 0x28])
let nb42bigEndian = Data([0x28, 0x42])
let tooBig = Data([0x44, 0xFA, 0x00, 0x00, 0x00])
print("opData: \(opData.toFloat())")
print("nb42: \(nb42.toFloat())")
print("nb42bigEndian: \(nb42bigEndian.toFloat(endianess: .big))")
print("tooBig: \(tooBig.toFloat())")
您可能会找到更快的方法,但这足以满足我的需求
这是我将字节数据转换为浮点数的代码。我尝试了本网站给出的所有答案。我得到这个“<44fa0000>”字节数据的指数值
static func returnFloatValue(mutableData:NSMutableData)->Float
{
let qtyRange = mutableData.subdataWithRange(NSMakeRange(0, 4))
let qtyString = String(qtyRange)
let qtyTrimString = qtyString.stringByTrimmingCharactersInSet(NSCharacterSet(charactersInString: "<>"))
let qtyValue = Float(strtoul(qtyTrimString, nil, 16)/10)
return qtyValue
}
谢谢
使用这个函数:
static func returnFloatValue(data: NSMutableData) -> Float {
let bytes = [UInt8](data as Data)
var f: Float = 0
memcpy(&f, bytes, 4)
return f
}
你可以在这里看到它的实际效果:
var initialValue: Float = 19.200
let data = NSMutableData(bytes: &initialValue, length: 4)
func returnFloatValue(data: NSMutableData) -> Float {
let bytes = [UInt8](data as Data)
var f: Float = 0
memcpy(&f, bytes, 4)
return f
}
var result:Float = returnFloatValue(data: data)
print("f=\(result)")// f=19.2
<44fa0000>
是 big-endian 内存表示
二进制浮点数 2000.0
。从中取回号码
数据,你必须首先将它读入 UInt32
,从
big-endian 托管字节顺序,然后将结果转换为
Float
.
在Swift 2中就是
func floatValueFromData(data: NSData) -> Float {
return unsafeBitCast(UInt32(bigEndian: UnsafePointer(data.bytes).memory), Float.self)
}
示例:
let bytes: [UInt8] = [0x44, 0xFA, 0x00, 0x00]
let data = NSData(bytes: bytes, length: 4)
print(data) // <44fa0000>
let f = floatValueFromData(data)
print(f) // 2000.0
在 Swift 3 中,您将使用 Data
而不是 NSData
,并且
unsafeBitCast
可以替换为 Float(bitPattern:)
初始值设定项:
func floatValue(data: Data) -> Float {
return Float(bitPattern: UInt32(bigEndian: data.withUnsafeBytes { [=12=].pointee } ))
}
在 Swift 5 中,Data
的 withUnsafeBytes()
方法使用(未类型化的)UnsafeRawBufferPointer
调用闭包,并且您可以 load()
来自原始内存的值:
func floatValue(data: Data) -> Float {
return Float(bitPattern: UInt32(bigEndian: data.withUnsafeBytes { [=13=].load(as: UInt32.self) }))
}
这是一些 swift 5:
let data = Data([0x44, 0xfa, 0x00, 0x00]) // 0x44fa0000
let floatNb:Float = data.withUnsafeBytes { [=10=].load(as: Float.self) }
// note that depending on the input endianess, you could add .reversed() to data
let floatNb:Float = data.reversed().withUnsafeBytes { [=10=].load(as: Float.self) }
警告:如果您的数据小于 4 个字节,此示例将抛出。
.
安全数据扩展:
extension Data {
enum Endianess {
case little
case big
}
func toFloat(endianess: Endianess = .little) -> Float? {
guard self.count <= 4 else { return nil }
switch endianess {
case .big:
let data = [UInt8](repeating: 0x00, count: 4-self.count) + self
return data.withUnsafeBytes { [=11=].load(as: Float.self) }
case .little:
let data = self + [UInt8](repeating: 0x00, count: 4-self.count)
return data.reversed().withUnsafeBytes { [=11=].load(as: Float.self) }
}
}
}
测试:
let opData = Data([0x44, 0xFA, 0x00, 0x00])
let nb42 = Data([0x42, 0x28])
let nb42bigEndian = Data([0x28, 0x42])
let tooBig = Data([0x44, 0xFA, 0x00, 0x00, 0x00])
print("opData: \(opData.toFloat())")
print("nb42: \(nb42.toFloat())")
print("nb42bigEndian: \(nb42bigEndian.toFloat(endianess: .big))")
print("tooBig: \(tooBig.toFloat())")
您可能会找到更快的方法,但这足以满足我的需求