Szathmáry László honlapja @ DEIK

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Working with big integers is very easy in Python. Let's see how it works in Scala.

scala> val x = 1234567890
x: Int = 1234567890 // it's an Int

scala> val x: BigInt = 1234567890 // let its type be BigInt
x: BigInt = 1234567890

scala> val x = 12345678909 // let's add one more digit
<console>:1: error: integer number too large // oops, that scalar is an int
val x = 12345678909
^

scala> val x: BigInt = 12345678909 // let's specify the type
<console>:1: error: integer number too large // err, nope
val x: BigInt = 12345678909
^

scala> val x = BigInt("12345678909") // solution: precise it as a string
x: scala.math.BigInt = 12345678909

The good news is that once a BigInt is created, you can work with it as if it were a normal integer:

scala> val x = BigInt("3473543254343544324")
x: scala.math.BigInt = 3473543254343544324

scala> x * x * x
res4: scala.math.BigInt = 41910045652080352561414700913973209412657131585450844224

scala> x.pow(3)
res5: scala.math.BigInt = 41910045652080352561414700913973209412657131585450844224

scala> x + 2
res6: scala.math.BigInt = 3473543254343544326

scala> x > 42
res7: Boolean = true

Generate big random primes

Generate a random prime with 100 bits:

scala> BigInt.probablePrime(100, scala.util.Random)
res9: scala.math.BigInt = 967064563528666024098824241151

Further examples

// how much is 2^1024
scala> BigInt(2).pow(1024)
res2: scala.math.BigInt = 1797693134862315907729305190789024733617976978942306572734
300811577326758055009631327084773224075360211201138798713933576587897688144166224928
474306394741243777678934248654852763022196012460941194530829520850057688381506823424
62881473913110540827237163350510684586298239947245938479716304835356329624224137216

// this example is from the book "Scala for the Impatient":
// "One way to create random file or directory names is to produce a random BigInt and
// convert it to base36."
scala> BigInt(100, scala.util.Random)
res3: scala.math.BigInt = 777764365538802043588777462195 // random BigInt with 100 bits

scala> BigInt(100, scala.util.Random).toString(36) // converted to base 36
res4: String = o79zx6lqjanmsqqbllg // here is the random string