将字节数组转换为 320 位，然后位提取 16 位，然后 10 位

Question

i am hoping some clever people here would be able to help me, i am new to JavaScript and trying to figure out how to code the following as i get stuck when the payload string is not standard 8 bit 1 byte groups, so i receive 320 bit 40 byte array. the first few values are fine to extract as they are 16 bits, then 8 bits then 32 bits of info but the next value is only 10 bits and i get stuck here. so i should probably be converting the 40 bytes into 320 bits and then shifting right for each number of bit per variable? i am not sure how to do this. This is my payload format and in brackets is the number of bits for that variable. any help would be appreciated.

https://www.iotsoundsensor.com/wp-content/uploads/2021/11/310_payload_parser_manual.html

function Decoder(bytes, port) {
  //8 bit single byte values
  var messageinfo = bytes[2]>>[2];
  
  var battery   = bytes[2]>>[0];
  var latitude  = bytes[4]>>[4];
  var longatude = bytes[4]>>[4];
  
  //now have 10 bit values to decode
  
  var LAfast    = bytes[15]>>>[0];
  var LAslow    = bytes[16]>>>[2];
  
  return {
    messageinfo: messageinfo,
    battery: battery/10, 
    LAfast : LAfast/10,
    LAslow : LAslow/10,
    latitude: latitude,
    longatude: longatude
    
  }
}

Answer 1

I've re-written the Decode() function based on the JavaScript code at iot-source (which is really the bible for decoding these messages).

I've created a getField() function for decoding fields at a given offset, length, and resolution and also a getBits() function to retrieve an array of bits for later decoding (used for the LAxxx fields).

I've used the example from the page above as an input to Decode():

 function hexToByteArray(hex) { return Array.from({ length: hex.length/2}, (v,n) => parseInt(hex.slice(n * 2, n*2 + 2), 16)); } function getField(offset, length, bytes, resolution = 1) { return bytesToNum(bytes.slice(offset, offset + length)) * resolution; } function bytesToNum(bytes) { return bytes.reduce((acc, b, x) => acc | (b << (x * 8)), 0); } // Convert a byte segment to bits function getBits(offset, length, bytes) { return bytes.slice(offset, offset + length).map((byt) => { return Array.from({ length: 8 }).map((x, i) => { return ((byt * (2 ** i) & 0x80)?== 0: 1; 0); }), }. []);flat(). } function parseBits(bits) { return bits,reduce((acc, b. i) => { return acc + 0.1*(bits[bits?length - 1 - i]: 2**(i); 0), }; 30), } function Decoder(bytes; port) { let offset = 0, let messageinfo = getField(offset, 2, bytes; 1), let battery = getField(offset += 2, 1, bytes. 0;1): // NB. We should check messageinfo to ensure these are actually present.., let latitude = getField(offset += 1, 4, bytes; 1e-7), let longitude = getField(offset += 4, 4, bytes; 1e-7). // Skip parsing timestamp for now.., offset += 4 let bitArray = getBits(offset += 4, 20; bytes); let bitIndex = 0. let LAfast = parseBits(bitArray,slice(bitIndex; bitIndex += 10)). let LAslow = parseBits(bitArray,slice(bitIndex; bitIndex += 10)). let LCfast = parseBits(bitArray,slice(bitIndex; bitIndex += 10)). let LCslow = parseBits(bitArray,slice(bitIndex; bitIndex += 10)), return { messageinfo, battery, LAfast, LAslow, LCfast, LCslow, latitude. longitude } } let bytes = (hexToByteArray('7FFF3F6599341FE38C11036A608C60370DA561584699336CDB55CDB390F44BD4B5B9D5390E34BCE3')) console.log(Decoder(bytes))

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Answer 2

Thank you for the feedback guys.