floor

Rounds the given value x to an integer towards negative infinity.

expect fun floor(x: Double): Double(source)

import kotlin.math.floor

fun main() {
    val values = listOf(3.7, -2.3, 5.0, -0.9)
    values.forEach { v ->
        val rounded = floor(v)   // rounds toward negative infinity
        println("floor($v) = $rounded")
    }
}

Source