Search code examples
scalajvmlanguage-design

What's Int.MaxValue between friends?

The max values of int, float and long in Scala are:

Int.MaxValue = 2147483647

Float.MaxValue = 3.4028235E38

Long.MaxValue = 9223372036854775807L

From the authors of Scala compiler, Keynote, PNW Scala 2013, slide 16 What's Int.MaxValue between friends?:

val x1: Float = Long.MaxValue
val x2: Float = Long.MaxValue - Int.MaxValue
println (x1 == x2)

// NO WONDER NOTHING WORKS

Why does this expression return true?

Solution

  • A Float is a 4-byte floating point value. Meanwhile a Long is an 8-byte value and an Int is also a 4-byte value. However, the way numbers are stored in 4-byte floating point values means that they have only around 8 digits of precision. Consequently, they do not have the capacity to store even the 4 most significant bytes (around 9-10 digits) of a Long regardless of the value of the least 4 significant bytes (another 9-10 digits).

    Consequently, the Float representation of the two expressions is the same, because the bits that differ are below the resolution of a Float. Hence the two values compare equal.