Bite the Bytes, WarpScript bitwise operators review

Sometimes, you need to process raw payloads. Extract a bit from an array of bytes. Build a byte array. If you play with Warp 10 MQTT plugin (now available on WarpFleet), you have to manipulate the payload you build on your IoT device.

Here is a useful cheat-sheet for bit and bytes manipulation in WarpScript.

Use LONG, BYTES

Most conversions from and to LONG or BYTES (bytes array) type exists. We will take an 8 bytes CAN frame as example payload. It contains two booleans, an integer, and a float:

This could be described in a C struct, using bit fields:

struct {
  unsigned int right_door_opened: 1;
  unsigned int left_door_opened: 1;
  char: 0;  //padding
  int batteryVoltage: 24;
  float batteryCurrent;
};

Decode payloads

payload.right_door_opened = 1;
payload.left_door_opened = 0;
payload.batteryVoltage = 351;
payload.batteryCurrent = -140.424;

The encoded frame could be represented as a long with value -4392016192336732415, or c30c6c8b00015f01 in hexadecimal. In WarpScript, you could decode everything in a few lines:

Of course, if you define the same C struct on another CPU, you might have to reverse endianness somewhere!

Encode payloads

Here is the code to build the byte array with the same content as the previous example:

Again, convert what you need to long, then to byte arrays, and use + to concatenate byte arrays. For booleans, use bitwise shift << and binary mask | and & to build long.

Debug

WarpScript also includes functions to represent byte array as strings. These functions are useful for debugging, checking endianness problems, and so on.

Conclusion

Like many languages, WarpScript allows to build or decode any kind of binary payload. If you want to check all available type conversions, read this tutorial!

Pierre Papin

Electronics engineer, fond of computer science, embedded solution developer.