Guide to separating the bytes of a number and placing them into an Uint8Array

Question

Guide to separating the bytes of a number and placing them into an Uint8Array

I am looking to convert a JavaScript number into the smallest possible uint8array representation.

For example :

65 535 = Uint8Array<[255,255]> (0b1111111111111111 = [0b11111111, 0b11111111])
12 356 = Uint8Array<[48,68]> (0b0011000001000100 = [0b00110000, 0b01000100])
1 142 =  Uint8Array<[4,118]> (0b0011000001000100 = [0b00000100, 0b01110110])
400 = Uint8Array<[1,144]> (0b0000000110010000 = [0b00000001, 0b10010000])
256 = Uint8Array<[1,0]> (0b0000000100000000 = [0b00000001, 0b00000000])
64 =  Uint8Array<[64]> (0b0000000001000000 = [0b01000000])
-1 = Uint8Array<[]> I do not handle negative numbers

I have been attempting to edit bytes individually as shown below:

const buffer : Uint8Array = new Uint8Array([0,0])
buffer[bytePos] &= ~(1<<bitToEdit); //to set at 0
buffer[bytePos] |= (1 <<bitToEdit) //to set at 1

The byte editing operation works, but I am unsure how to extract bytes from the number and populate them into this array.

javascript typescript binary

Answer 1

Answer №1

To achieve this functionality, you can utilize the BigInt feature along with the modulus operator (%) and the Uint8Array.from method.

In cases involving negative numbers or when dealing with a value of 0, the code provided will result in an empty Uint8Array containing zero elements. The output of this code is in Big Endian format, similar to the example given, achieved by reversing the byte array.

function convertToByteArray(number) {
  let bigIntNumber = BigInt(number);
  let byteArrayResult = [];
  while (bigIntNumber > 0n) {
    byteArrayResult.push(Number(bigIntNumber % 0x100n));
    bigIntNumber /= 0x100n;
  }
  return Uint8Array.from(byteArrayResult.reverse());
}

console.log(convertToByteArray(
  0x01_00_00_00_00_00_00_00_03n
)) // Output: Uint8Array(9) [ 1, 0, 0, 0, 0, 0, 0, 0, 3 ]

Answer 2

To achieve this functionality, you can utilize the BigInt feature along with the modulus operator (%) and the Uint8Array.from method.

In cases involving negative numbers or when dealing with a value of 0, the code provided will result in an empty Uint8Array containing zero elements. The output of this code is in Big Endian format, similar to the example given, achieved by reversing the byte array.

function convertToByteArray(number) {
  let bigIntNumber = BigInt(number);
  let byteArrayResult = [];
  while (bigIntNumber > 0n) {
    byteArrayResult.push(Number(bigIntNumber % 0x100n));
    bigIntNumber /= 0x100n;
  }
  return Uint8Array.from(byteArrayResult.reverse());
}

console.log(convertToByteArray(
  0x01_00_00_00_00_00_00_00_03n
)) // Output: Uint8Array(9) [ 1, 0, 0, 0, 0, 0, 0, 0, 3 ]

Guide to separating the bytes of a number and placing them into an Uint8Array

Answer №1

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