如何在Swift中解析由蓝牙设备发送的浮动消息? [英] How to parse a float, sent by a Bluetooth device, in Swift?

问题描述

在我的iOS应用上，我需要对蓝牙接收的Float值进行解码，并从其他设备(不是iOS)获取4个字节，因此我需要便携式" 4字节Float格式.目前，发件人正在使用以下格式:

On my iOS app I need to decode a Float value received by bluetooth and taking 4 bytes from a different device ( not iOS) so I need a "portable" 4-byte Float format . For now the sender is using this format:

数据编码:0xCCBBAAEE -0xEE:指数，1个有符号字节. -0xCCBBAA:尾数，3个有符号字节.

Data codification: 0xCCBBAAEE - 0xEE: Exponent, 1 signed byte. - 0xCCBBAA: Mantissa, 3 signed bytes.

我的问题是:如何从指数和尾数中构造一个(ios)浮点数?

My question is: how can I construct an (ios) Float from such Exponent and the Mantissa?

具有以下初始化程序: public init(符号:FloatingPointSign，指数:Int，有效数字:Float)

in iOS Float has this initializer: public init(sign: FloatingPointSign, exponent: Int, significand: Float)

我可以轻松地从带符号的尾数中计算出符号参数，从带符号的指数中计算出Exp参数，但是有效参数采用了Float，但是有效参数是Float，我只收到了3个字节的尾数.

I can easily work out the sign param from the signed Mantissa, the Exp param from the signed Exponent but the significant parameter takes a Float BUT the significand param is a Float and I only receive a 3-bytes mantissa.

推荐答案

假设您正在遵循

Assuming you are following the standard IEEE format, which really looks you are — I have a hard time believing this Bluetooth device of yours would use anything else on the wire — then try this initializer instead (available since Swift 3):

init(
    sign: FloatingPointSign, 
    exponentBitPattern: UInt,
    significandBitPattern: UInt32
)

这由 BinaryFloatingPoint 协议定义:

This is defined by the BinaryFloatingPoint protocol:

以exponentBitPattern和significandBitPattern传递的值以IEEE 754规范定义的二进制交换格式解释.

The values passed as exponentBitPattern and significandBitPattern are interpreted in the binary interchange format defined by the IEEE 754 specification.

上面提到的(单精度)Float的IEEE 754是:

The IEEE 754 mentioned above for (single precision) Float is:

• 符号位:1位
• 指数宽度:8位
• 有效精度:24位(显式存储23位)

其他 Float初始化程序也应该可以正常工作:

This other Float initializer should work fine as well:

init(bitPattern: UInt32)

在这两种情况下，只要注意 大端与小端 问题，您应该会很好;)

In both cases, just watch out for big- vs little-endianness issues and you should be fine ;)

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