Starter project: Initializers for converting UnsafePointers to integers

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1

Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

https://bugs.swift.org/browse/SR-131

Dmitri

···

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/

2

I'm looking for a good starter project, so normally I would be interested
in taking this, but I'm not sure I can think of a good motivation for it.
UnsafePointer's advanceBy and distanceTo functions take care of pointer
arithmetic more safely than converting to int would, and the
debugDescription property can get you the address for debugging purposes.

Considering that everything that goes through the swift-evolution process
needs to have a motivation, is there a use case for this that I'm not
thinking of?

···

On Mon, Dec 7, 2015 at 4:45 PM, Dmitri Gribenko via swift-dev < swift-dev@swift.org> wrote:

Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

[SR-131] Initializers for converting UnsafePointers to integers · Issue #42753 · apple/swift · GitHub

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/
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swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

3

When writing high-performance code, it is fairly common to check the alignment of pointers so that initial elements can be processed until some suitable alignment is reached to use a faster implementation, or to verify that a fast algorithm can be used.

···

On Dec 8, 2015, at 10:59 AM, Michael Buckley via swift-dev <swift-dev@swift.org> wrote:

I'm looking for a good starter project, so normally I would be interested in taking this, but I'm not sure I can think of a good motivation for it. UnsafePointer's advanceBy and distanceTo functions take care of pointer arithmetic more safely than converting to int would, and the debugDescription property can get you the address for debugging purposes.

Considering that everything that goes through the swift-evolution process needs to have a motivation, is there a use case for this that I'm not thinking of?

On Mon, Dec 7, 2015 at 4:45 PM, Dmitri Gribenko via swift-dev <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote:
Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

[SR-131] Initializers for converting UnsafePointers to integers · Issue #42753 · apple/swift · GitHub

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com <mailto:gribozavr@gmail.com>>*/
_______________________________________________
swift-dev mailing list
swift-dev@swift.org <mailto:swift-dev@swift.org>
https://lists.swift.org/mailman/listinfo/swift-dev

_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

4

The one I can think of is "sometimes a C API only lets you pass data as an Int (intptr_t) or as an UnsafeMutablePointer (void *), and you have the other kind of data". That said, it does seem to be sort of a niche use case.

Jordan

···

On Dec 8, 2015, at 7:59, Michael Buckley via swift-dev <swift-dev@swift.org> wrote:

I'm looking for a good starter project, so normally I would be interested in taking this, but I'm not sure I can think of a good motivation for it. UnsafePointer's advanceBy and distanceTo functions take care of pointer arithmetic more safely than converting to int would, and the debugDescription property can get you the address for debugging purposes.

Considering that everything that goes through the swift-evolution process needs to have a motivation, is there a use case for this that I'm not thinking of?

On Mon, Dec 7, 2015 at 4:45 PM, Dmitri Gribenko via swift-dev <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote:
Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

[SR-131] Initializers for converting UnsafePointers to integers · Issue #42753 · apple/swift · GitHub

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com <mailto:gribozavr@gmail.com>>*/
_______________________________________________
swift-dev mailing list
swift-dev@swift.org <mailto:swift-dev@swift.org>
https://lists.swift.org/mailman/listinfo/swift-dev

_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

5

Checking alignment good use case, which I did not consider. Not to turn
this into a swift-evolution topic, but couldn't this use case be covered by
adding functions to UnsafePointer? I'm thinking something like this.

func distanceToBoundary(_ boundary: Int) -> Distance {
    return Builtin.ptrtoint_Word(self._rawValue) % boundary
}

func isAlignedToBoundary(_ boundary: Int) -> Boolean {
    return distanceToBoundary(boundary) == 0
}

I'll admit I don't have a lot of experience working with algorithms which
check pointer alignment. If you need a check that requires a more
complicated equation, then yeah, converting UnsafePointers to Ints is
probably the best solution. But if possible, it's probably best to avoid
requiring users to convert to int and back. They not only need to write
less code if UnsafePointers can take care of this for them, but it also
prevents subtle bugs they may write. (E.g. Converting 2 UnsafePointers to
UInts and then subtracting them to find the distance, but subtracting the
larger pointer from the smaller one).

···

On Tue, Dec 8, 2015 at 8:45 AM, Stephen Canon <scanon@apple.com> wrote:

When writing high-performance code, it is fairly common to check the
alignment of pointers so that initial elements can be processed until some
suitable alignment is reached to use a faster implementation, or to verify
that a fast algorithm can be used.

On Dec 8, 2015, at 10:59 AM, Michael Buckley via swift-dev < > swift-dev@swift.org> wrote:

I'm looking for a good starter project, so normally I would be interested
in taking this, but I'm not sure I can think of a good motivation for it.
UnsafePointer's advanceBy and distanceTo functions take care of pointer
arithmetic more safely than converting to int would, and the
debugDescription property can get you the address for debugging purposes.

Considering that everything that goes through the swift-evolution process
needs to have a motivation, is there a use case for this that I'm not
thinking of?

On Mon, Dec 7, 2015 at 4:45 PM, Dmitri Gribenko via swift-dev < > swift-dev@swift.org> wrote:

Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

[SR-131] Initializers for converting UnsafePointers to integers · Issue #42753 · apple/swift · GitHub

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/
_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

6

Yeah, that makes sense. If your C API requires an intptr_t, you can't solve
that problem by adding more functions to UnsafePointer. I'll go ahead and
start a discussion over on swift-evolution. Thanks!

···

On Tue, Dec 8, 2015 at 3:07 PM, Jordan Rose <jordan_rose@apple.com> wrote:

The one I can think of is "sometimes a C API only lets you pass data as an
Int (intptr_t) or as an UnsafeMutablePointer (void *), and you have the
other kind of data". That said, it does seem to be sort of a niche use case.

Jordan

On Dec 8, 2015, at 7:59, Michael Buckley via swift-dev < > swift-dev@swift.org> wrote:

I'm looking for a good starter project, so normally I would be interested
in taking this, but I'm not sure I can think of a good motivation for it.
UnsafePointer's advanceBy and distanceTo functions take care of pointer
arithmetic more safely than converting to int would, and the
debugDescription property can get you the address for debugging purposes.

Considering that everything that goes through the swift-evolution process
needs to have a motivation, is there a use case for this that I'm not
thinking of?

On Mon, Dec 7, 2015 at 4:45 PM, Dmitri Gribenko via swift-dev < > swift-dev@swift.org> wrote:

Hi everyone,

The standard library has bitPattern initializers on pointers. But we
are missing initializers to create integers from pointers.

Someone needs to propose these APIs, walk them through
swift-evolution, write a patch for the library and add tests.

extension UInt {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = UInt(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

extension Int {
  init<T>(bitPattern: UnsafePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }

  init<T>(bitPattern: UnsafeMutablePointer<T>) {
    self = Int(Builtin.ptrtoint_Word(bitPattern._rawValue))
  }
}

[SR-131] Initializers for converting UnsafePointers to integers · Issue #42753 · apple/swift · GitHub

Dmitri

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/
_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev

_______________________________________________
swift-dev mailing list
swift-dev@swift.org
https://lists.swift.org/mailman/listinfo/swift-dev