Bytes conversion

Convert integer to bytes

Built-in solution

To convert a integer into 4 bytes, we can utilize ByteBuffer as following:

    val size = 4
    val buffer = ByteBuffer.allocate(size)
    buffer.putInt(num)
    return buffer.array()

Notice: if allocating the size lower than 4, it will through BufferOverflowException.

Manual solution

To convert integer manually:

    val data = ByteArray(size)
    data[0] = (num ushr 24 and 0xFF).toByte()
    data[1] = (num ushr 16 and 0xFF).toByte()
    data[2] = (num ushr 8 and 0xFF).toByte()
    data[3] = (num ushr 0 and 0xFF).toByte()

It's useful when we need to convert integer into arbitrary size of bytes (< 4). It can be generalized for different bytes:

fun intToBytes(num: Int, size: Int): ByteArray {
    val data = ByteArray(size)

    var shifted = num
    for (i in size - 1 downTo  0) {
        data[i] = (shifted and 0xFF).toByte()
        shifted = shifted shr 8
    }

    return data
}

Reference: https://stackoverflow.com/questions/1735840/how-do-i-split-an-integer-into-2-byte-binary

Convert bytes to integer

Built-in solution

    val buffer = ByteBuffer.wrap(bytes)
    return buffer.int

Reference: https://mkyong.com/java/java-convert-byte-to-int-and-vice-versa/

Manual solution

To convert bytes array back to integer, we can shift all bytes left and concatenate them by or:

    var result = 0

    result = result or (bytes[3].toInt() and 0XFF shl 0)
    result = result or (bytes[2].toInt() and 0XFF shl 8)
    result = result or (bytes[1].toInt() and 0XFF shl 16)
    result = result or (bytes[0].toInt() and 0XFF shl 24)
    
    return result

It can be generalized for different bytes:

fun bytesToInt(bytes: ByteArray): Int {
    var result = 0
    val size = bytes.size
    var shift = 0

    for (i in size - 1 downTo  0) {
        result = result or (bytes[i].toInt() and 0XFF shl shift)
        shift += 8
    }

    return result
}

Convert long to bytes

Built-in solution

    val buffer = ByteBuffer.allocate(java.lang.Long.BYTES)
    buffer.putLong(num)
    return buffer.array()

Reference: https://stackoverflow.com/questions/4485128/how-do-i-convert-long-to-byte-and-back-in-java

Manual solution

Same as converting integer to bytes but the size of bytes should be 8 to avoid overflow.

Convert bytes to long

Built-in solution

    val buffer = ByteBuffer.wrap(bytes)
    return buffer.long

Manual solution

Same as converting bytes to integer but each byte should convert to Long before shifting and concatenating together.

What does AND 0xFF do?

0xFF is a number represented in the hexadecimal numeral system (base 16). It's composed of two F numbers in hex. As we know, F in hex is equivalent to 1111 in the binary numeral system. So, 0xFF in binary is 11111111.

If byte is 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 which is more than 8 bits, then & 0xFF will essentially give you the last 8 bits of the value.

    0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
 &  0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1
    -------------------------------
    0 0 0 0 0 0 0 0 0 1 0 1 0 1 0 1

Reference: https://stackoverflow.com/questions/14713102/what-does-and-0xff-do

Represent bytes array as String of bits

To represent single Byte as String of bits:

fun byteToString(byte: Byte): String {
    return String.format("%8s", Integer.toBinaryString(byte.toInt() and 0xFF))
        .replace(' ', '0')
}

For ByteArray, simply apply above function through all bytes in array:

fun byteArrayToString(byte: ByteArray): String {
    return byte.joinToString(" ") { byteToString(it) }
}

chienkanglu / byteutils Goto Github PK

byteutils's Introduction

Bytes conversion

Convert integer to bytes

Built-in solution

Manual solution

Convert bytes to integer

Built-in solution

Manual solution

Convert long to bytes

Built-in solution

Manual solution

Convert bytes to long

Built-in solution

Manual solution

What does AND 0xFF do?

Represent bytes array as String of bits

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