SIP 15: How to unsigned integer values

[Heiko Seeberger]

Hey,

Reading through SIP 15 I stumbled over "New numeric classes, such as unsigned ints. There would no longer need to be a boxing overhead for such classes. So this is similar to value classes in .NET". What's meant here? Transforming the range from 0 to 4294967295? If so, how would that work?

Thanks

Heiko

--

Heiko Seeberger
Twitter: @hseeberger

Blog: heikoseeberger.name

Company: Typesafe - The software stack for applications that scale
Author of "Durchstarten mit Scala, a tutorial-style Scala book"

[Paul Phillips]

On Thu, Sep 6, 2012 at 12:24 PM, Heiko Seeberger <heiko.s...@gmail.com> wrote:

Hey,

Reading through SIP 15 I stumbled over "New numeric classes, such as unsigned ints. There would no longer need to be a boxing overhead for such classes. So this is similar to value classes in .NET". What's meant here? Transforming the range from 0 to 4294967295? If so, how would that work?

% scala3

Welcome to Scala version 2.11.0-20120905-004841-4f9851d1fd (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_31).

Type in expressions to have them evaluated.

Type :help for more information.

scala> final case class UInt(val x: Int) extends AnyVal with Ordered[UInt] {

  def toLong = 0x00000000FFFFFFFFL & x

  def compare(other: UInt) = toLong compare other.toLong

  def +(other: UInt) = UInt((toLong + other.toLong).toInt)

  override def toString = toLong + "(u)"

}

defined class UInt

scala> implicit def mkUInt(x: Int) = new UInt(x)

wmkUInt: (x: Int)UInt

scala> def f(x: UInt, y: UInt) = println(s"$x < $y ? ${x < y}")

f: (x: UInt, y: UInt)Unit

scala> 1 << 30

res0: Int = 1073741824

scala> 1 << 31

res1: Int = -2147483648

scala> f(1 << 30, 1 << 31)

1073741824(u) < 2147483648(u) ? true

scala> UInt(1 << 30) + UInt(1 << 31)

res3: UInt = 3221225472(u)

scala> class A { def f(x: UInt, y: UInt) = x + y }

defined class A

scala> :javap -v A

Compiled from "<console>"

public class A extends java.lang.Object

...

public int f(int, int);

  Code:

   Stack=3, Locals=3, Args_size=3

   0: getstatic #13; //Field UInt$.MODULE$:LUInt$;

   3: iload_1

   4: iload_2

   5: invokevirtual #16; //Method UInt$.extension$$plus:(II)I

   8: ireturn

 

scala> :javap -v UInt$

...

public final long extension$toLong(int);

   0: ldc2_w  #57; //long 4294967295l

   3: iload_1

   4: i2l

   5: land

   6: lreturn

public final int extension$$plus(int, int);

   0: aload_0

   1: iload_1

   2: invokevirtual #70; //Method extension$toLong:(I)J

   5: aload_0

   6: iload_2

   7: invokevirtual #70; //Method extension$toLong:(I)J

   10:  ladd

   11:  l2i

   12:  ireturn

[Erik Osheim]

On Thu, Sep 06, 2012 at 09:24:11PM +0200, Heiko Seeberger wrote:
> Reading through SIP 15 I stumbled over "New numeric classes, such as
> unsigned ints. There would no longer need to be a boxing overhead for
> such classes. So this is similar to value classes in .NET". What's
> meant here? Transforming the range from 0 to 4294967295? If so, how
> would that work?

Attached is an example I threw together. I only tested it a bit in the
REPL, but I think it illustrates the idea well enough.

scala> val x = new Unsigned(1000)
x: Unsigned = 1000

scala> val y = 1000
y: Int = 1000

scala> x*x*x*x
res0: Unsigned = 3567587328

scala> y*y*y*y
res1: Int = -727379968

I haven't really tested how well these kind of unsigned numbers
currently perform (the extension methods aren't final and are resolved
via invokevirtual, which probably isn't ideal), but I can confirm that
in most normal cases they are not boxed.

Of course, once you want to use arrays you will need to work with the
underlying type (e.g. Int) or face serious boxing.

-- Erik

[Erik Osheim]

On Thu, Sep 06, 2012 at 04:34:00PM -0400, Erik Osheim wrote:
> Attached is an example I threw together. I only tested it a bit in the
> REPL, but I think it illustrates the idea well enough.

Of course, Paul beat me to it (and had a better implementation of
toLong to boot)!

-- Erik

[Som Snytt]

If Typesafe opens an online store, I hope they carry t-shirts that say, "Paul beat me to it."

Another one I'd like, because I don't know where else to apply this slogan: "paulp fiction".

[Sadache Aldrobi]

On Thu, Sep 6, 2012 at 10:39 PM, Som Snytt <som....@gmail.com> wrote:

If Typesafe opens an online store, I hope they carry t-shirts that say, "Paul beat me to it."

Another one I'd like, because I don't know where else to apply this slogan: "paulp fiction".

I'd buy the latter.

 

On Thu, Sep 6, 2012 at 1:35 PM, Erik Osheim <er...@plastic-idolatry.com> wrote:

On Thu, Sep 06, 2012 at 04:34:00PM -0400, Erik Osheim wrote:
> Attached is an example I threw together. I only tested it a bit in the
> REPL, but I think it illustrates the idea well enough.

Of course, Paul beat me to it (and had a better implementation of
toLong to boot)!

-- Erik

--
www.sadekdrobi.com
ʎdoɹʇuǝ

[martin odersky]

For a complete implementation of UInt/ULong, including the tricky bit of how to do unsigned long division/remainder, see

https://github.com/odersky/scala/commit/7530291f5fb715c2e4f028885b69daa1d1ead503

Turning Uint into a value class is the last commit here:

https://github.com/odersky/scala/tree/topic/unsigned

I think indeed it would be promising to add this to the standard distribution.

Cheers

 - Martin

[Rich Oliver]

Am I right in saying that

val x: UInt = - 5

would still compile? Funnily I was just writing my own even Int class:

class IntEven(k: Int)    {
      val e = {require(k.isEven); k}     
  }
 implicit def IntEvenToInt(inp: IntEven): Int = inp.e

implicit class RichInt2(n: Int) extends Unchanged[Int]
   {
      override def unchanged: Int = n
      def isOdd: Boolean = if (n % 2 == 1) true else false
      def isEven: Boolean = if (n % 2 == 0) true else false
   }

I presume there's no way to implement IntEven as a value class