Human Readable Data Size Formatter for Kotlin Multiplatform (uses Common API only)

DataSizeFormatter.kt

package datasizeformatter

import kotlin.math.abs
import kotlin.math.pow
import kotlin.math.roundToLong

/**
 * Format a human-readable representation of data size, in binary base form.
 * e.g. 1024 -> 1 KiB
 * @param byteCount The number of bytes to represent in human-readable form. `Long.MIN_VALUE` is unsupported.
 * @param decimalPlaces The number of digits to round the resulting scale to
 * @param zeroPadFraction whether to add trailing zeroes if they could otherwise be numerically truncated.
 * e.g. for the value `3.1` if [decimalPlaces] is set to 3 and [zeroPadFraction] is `true` would be shown as `3.100`.
 */
fun formatBinarySize(
    byteCount: Long,
    decimalPlaces: Int = 2,
    zeroPadFraction: Boolean = false
): String {
    require(byteCount>Long.MIN_VALUE) { "Out of range" }
    require(decimalPlaces>=0) { "Negative decimal places unsupported" }
    val isNegative = byteCount < 0
    val absByteCount = abs(byteCount)
    return if (absByteCount < 1024) {
        "$byteCount B"
    } else {
        val zeroBitCount: Int = (63 - absByteCount.countLeadingZeroBits()) / 10
        val absNumber: Double = absByteCount.toDouble() / (1L shl zeroBitCount * 10)
        val roundingFactor: Int = 10.0.pow(decimalPlaces).toInt()
        val absRoundedNumberString = with((absNumber * roundingFactor).roundToLong().toString()) {
            val splitIndex = length - decimalPlaces - 1
            val wholeString = substring(0..splitIndex)
            val fractionString = with(substring(splitIndex + 1)) {
                if (zeroPadFraction) this else dropLastWhile { digit -> digit == '0' }
            }
            if (fractionString.isEmpty()) wholeString else "$wholeString.$fractionString"
        }
        val roundedNumberString = if(isNegative) "-$absRoundedNumberString" else absRoundedNumberString
        "$roundedNumberString ${"KMGTPE"[zeroBitCount - 1]}iB"
    }
}

Tested OK on JVM, JS and Native targets with:

assertEquals(expected = "0 B", actual = formatBinarySize(byteCount = -0))
assertEquals(expected = "1 KiB", actual = formatBinarySize(byteCount = 1024))
assertEquals(expected = "1.00 KiB", actual = formatBinarySize(byteCount = 1024, zeroPadFraction = true))
assertEquals(expected = "4 KiB", actual = formatBinarySize(byteCount = 4096))
assertEquals(expected = "1.00 MiB", actual = formatBinarySize(1048576, zeroPadFraction = true))
assertEquals(expected = "1.500 MiB", actual = formatBinarySize(1572864, decimalPlaces = 3, zeroPadFraction = true))
assertEquals(expected = "1.00009 PiB", actual = formatBinarySize(1126000000000000, decimalPlaces = 5, zeroPadFraction = false))
assertEquals(expected = "-1.00009 PiB", actual = formatBinarySize(-1126000000000000, decimalPlaces = 5, zeroPadFraction = false))
assertEquals(expected = "-47 B", actual = formatBinarySize(-47))