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Float hierarchy for 64-bit Spur

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Eliot Miranda-2

Float hierarchy for 64-bit Spur

Hi All,

64-bit Spur can usefully provide an immediate float, a 61-bit subset of the ieee double precision float. The scheme steals bits from the mantissa to use for the immediate's 3-bit tag pattern. So values have the same precision as ieee doubles, but can only represent the subset with exponents between 10^-38 and 10^38, the single-precision range. The issue here is how to organize the class hierarchy.

The approach that looks best to me is to modify class Float to be an abstract class, and add two subclasses, BoxedFloat and SmallFloat, such that existing boxed instances of Float outside the SmallFloat range will become instances of BoxedFloat and instances within that range will be replaced by references to the relevant SmallFloat.

With this approach ...

- Float pi etc can still be used, even though they will answer instances of SmallFloat. But tests such as "self assert: result class == Float." will need to be rewritten to e.g. "self assert: result isFloat".

- BoxedFloat and SmallFloat will not be mentioned much at all since floats print themselves literally, and so the fact that the classes have changed won't be obvious.

- the boxed Float primitives (receiver is a boxed float) live in BoxedFloat and the immediate ones live in SmallFloat. Making SmallFloat a subclass of Float poses problems for all the primitives that do a super send to retry, since the boxed Float prims will be above the unboxed ones and so the boxed ones would have to test for an immediate receiver.

An alternative, that VW took (because it has both Float and Double) is to add a superclass, e.g. LimitedPrecisionReal, move most of the methods into it, and keep Float as Float, and add SmallFloat as a subclass of LimitedPrecisionReal. Then while class-side methods such as pi would likely be implemented in LimitedPrecisionReal class, sends to Float to access them find them via inheritance. An automatic reorganization which moves only primitives out of LimitedPrecisionReal is easy to write.

Thoughts?

best,

Eliot

Ben Coman

Re: Float hierarchy for 64-bit Spur

Eliot Miranda wrote:
> Hi All,
>
> 64-bit Spur can usefully provide an immediate float, a 61-bit subset
> of the ieee double precision float.

I wonder if class SmallDouble would be more intention revealing?

In practice 61 bits will be "more than enough"(tm) for anyone. But I can
envisage in a business environment environment software needing to
comply with (sometimes irrelevant) feature checklists, with one of those
likely being full 64 bit compliant IEEE Doubles. Can Pharo aim to have
such a class, to which 61 bit floats are auto-promoted as required?

> The scheme steals bits from the
> mantissa to use for the immediate's 3-bit tag pattern. So values have
> the same precision as ieee doubles, but can only represent the subset
> with exponents between 10^-38 and 10^38, the single-precision range.
> The issue here is how to organize the class hierarchy.

>
> The approach that looks best to me is to modify class Float to be an
> abstract class, and add two subclasses, BoxedFloat and SmallFloat, such
> that existing boxed instances of Float outside the SmallFloat range will
> become instances of BoxedFloat and instances within that range will be
> replaced by references to the relevant SmallFloat.
>

My first few pages of search results lead to a few references in
conversation, but nothing that described what a boxed float is. Can
someone explain?

btw, http://www.ctan.org/pkg/float
also mentioned boxed float, ruled float and plaintop float
Anyone familiar with those?

> With this approach ...
>
> - Float pi etc can still be used, even though they will answer instances
> of SmallFloat. But tests such as "self assert: result class == Float."
> will need to be rewritten to e.g. "self assert: result isFloat".
>
> - BoxedFloat and SmallFloat will not be mentioned much at all since
> floats print themselves literally, and so the fact that the classes have
> changed won't be obvious.
>
> - the boxed Float primitives (receiver is a boxed float) live in
> BoxedFloat and the immediate ones live in SmallFloat. Making SmallFloat
> a subclass of Float poses problems for all the primitives that do a
> super send to retry, since the boxed Float prims will be above the
> unboxed ones and so the boxed ones would have to test for an immediate
> receiver.
>
>
> An alternative, that VW took (because it has both Float and Double) is
> to add a superclass, e.g. LimitedPrecisionReal, move most of the methods
> into it, and keep Float as Float, and add SmallFloat as a subclass of
> LimitedPrecisionReal. Then while class-side methods such as pi would
> likely be implemented in LimitedPrecisionReal class, sends to Float to
> access them find them via inheritance. An automatic reorganization
> which moves only primitives out of LimitedPrecisionReal is easy to write.
>

A Float is defined as a limited precision real [1] having several types
of precision, so I like the first option.

[1] http://en.wikipedia.org/wiki/Floating_point

cheers -ben

David T. Lewis

Re: [squeak-dev] Float hierarchy for 64-bit Spur

In reply to this post by Eliot Miranda-2

On Thu, Nov 20, 2014 at 05:51:42PM -0800, Eliot Miranda wrote:

> Hi All,
>
> 64-bit Spur can usefully provide an immediate float, a 61-bit subset of
> the ieee double precision float. The scheme steals bits from the mantissa
> to use for the immediate's 3-bit tag pattern. So values have the same
> precision as ieee doubles, but can only represent the subset with exponents
> between 10^-38 and 10^38, the single-precision range. The issue here is
> how to organize the class hierarchy.
>
> The approach that looks best to me is to modify class Float to be an
> abstract class, and add two subclasses, BoxedFloat and SmallFloat, such
> that existing boxed instances of Float outside the SmallFloat range will
> become instances of BoxedFloat and instances within that range will be
> replaced by references to the relevant SmallFloat.
>
> With this approach ...
>
> - Float pi etc can still be used, even though they will answer instances of
> SmallFloat. But tests such as "self assert: result class == Float." will
> need to be rewritten to e.g. "self assert: result isFloat".
>
> - BoxedFloat and SmallFloat will not be mentioned much at all since floats
> print themselves literally, and so the fact that the classes have changed
> won't be obvious.
>
> - the boxed Float primitives (receiver is a boxed float) live in BoxedFloat
> and the immediate ones live in SmallFloat. Making SmallFloat a subclass of
> Float poses problems for all the primitives that do a super send to retry,
> since the boxed Float prims will be above the unboxed ones and so the boxed
> ones would have to test for an immediate receiver.
>
>
> An alternative, that VW took (because it has both Float and Double) is to
> add a superclass, e.g. LimitedPrecisionReal, move most of the methods into
> it, and keep Float as Float, and add SmallFloat as a subclass of
> LimitedPrecisionReal. Then while class-side methods such as pi would
> likely be implemented in LimitedPrecisionReal class, sends to Float to
> access them find them via inheritance. An automatic reorganization which
> moves only primitives out of LimitedPrecisionReal is easy to write.
>
> Thoughts?

I have always felt that the mapping of Float to 64-bit double and FloatArray
to 32-bit float is awkward. It may be that 32-bit floats are becoming less
relevant nowadays, but if short float values are still important, then it
would be nice to be able to represent them directly. I like the idea of having
a Float class and a Double class to represent the two most common representations.
A class hierarchy that could potentially support this sounds like a good idea to me.

I have no experience with VW, but a LimitedPrecisionReal hierachy sounds like a
reasonable approach.

Dave

Ben Coman

Re: [Vm-dev] Re: [squeak-dev] Float hierarchy for 64-bit Spur

Bert Freudenberg wrote:

>
>
>
> ------------------------------------------------------------------------
>
>
> On 21.11.2014, at 04:19, David T. Lewis <[hidden email]> wrote:
>
>> On Thu, Nov 20, 2014 at 05:51:42PM -0800, Eliot Miranda wrote:
>>> Hi All,
>>>
>>> 64-bit Spur can usefully provide an immediate float, a 61-bit subset of
>>> the ieee double precision float. The scheme steals bits from the mantissa
>>> to use for the immediate's 3-bit tag pattern. So values have the same
>>> precision as ieee doubles, but can only represent the subset with exponents
>>> between 10^-38 and 10^38, the single-precision range. The issue here is
>>> how to organize the class hierarchy.
>>>
>>> The approach that looks best to me is to modify class Float to be an
>>> abstract class, and add two subclasses, BoxedFloat and SmallFloat, such
>>> that existing boxed instances of Float outside the SmallFloat range will
>>> become instances of BoxedFloat and instances within that range will be
>>> replaced by references to the relevant SmallFloat.
>>>
>>> With this approach ...
>>>
>>> - Float pi etc can still be used, even though they will answer instances of
>>> SmallFloat. But tests such as "self assert: result class == Float." will
>>> need to be rewritten to e.g. "self assert: result isFloat".
>>>
>>> - BoxedFloat and SmallFloat will not be mentioned much at all since floats
>>> print themselves literally, and so the fact that the classes have changed
>>> won't be obvious.
>>>
>>> - the boxed Float primitives (receiver is a boxed float) live in BoxedFloat
>>> and the immediate ones live in SmallFloat. Making SmallFloat a subclass of
>>> Float poses problems for all the primitives that do a super send to retry,
>>> since the boxed Float prims will be above the unboxed ones and so the boxed
>>> ones would have to test for an immediate receiver.
>>>
>>>
>>> An alternative, that VW took (because it has both Float and Double) is to
>>> add a superclass, e.g. LimitedPrecisionReal, move most of the methods into
>>> it, and keep Float as Float, and add SmallFloat as a subclass of
>>> LimitedPrecisionReal. Then while class-side methods such as pi would
>>> likely be implemented in LimitedPrecisionReal class, sends to Float to
>>> access them find them via inheritance. An automatic reorganization which
>>> moves only primitives out of LimitedPrecisionReal is easy to write.
>>>
>>> Thoughts?
>> I have always felt that the mapping of Float to 64-bit double and FloatArray
>> to 32-bit float is awkward. It may be that 32-bit floats are becoming less
>> relevant nowadays, but if short float values are still important, then it
>> would be nice to be able to represent them directly. I like the idea of having
>> a Float class and a Double class to represent the two most common representations.
>> A class hierarchy that could potentially support this sounds like a good idea to me.
>>
>> I have no experience with VW, but a LimitedPrecisionReal hierachy sounds like a
>> reasonable approach.
>>
>> Dave
>
> I'd suggest BoxedDouble and ImmediateDouble as names for the concrete subclasses (*). Names do mean something. (**)
>

This is a nice idea, except we have the legacy of SmallInteger and
LargeInteger, and I don't like the inconsistency of Float not following
the same rule. The boxing/unboxing can be covered in the class comment.
Unless you want to change to BoxedInteger and ImmediateInteger ?

cheers -ben

> You're right about the FloatArray confusion. However, note that the IEEE standard calls it single and double. It's only C using "float" to mean "single precision".
>
> I'd name the abstract superclass Float, for readability, and the isFloat test etc. Also: "Float pi" reads a lot nicer than anything else. I don't see the need for having a deep LimitedPrecisionReal - Float - BoxedDouble/ImmediateDouble deep hierarchy now.
>
> If we ever add single-precision floats, we should name them BoxedSingle and ImmediateSingle. At that point we might want a Single superclass and a LimitedPrecisionReal supersuperclass, but we can cross that bridge when we get there.
>
> - Bert -
>
> (*) Since we're not going to see the class names often, we could even spell it out as BoxedDoublePrecisionFloat and ImmediateDoublePrecisionFloat. Only half joking. It would make the relation to the abstract Float very clear.
>
> (**) We could also try to make the names googleable. I was surprised to not get a good hit for "boxed immediate". Only "boxed unboxed" finds it. Maybe there are two better words?
>

Eliot Miranda-2

Re: [squeak-dev] Float hierarchy for 64-bit Spur

In reply to this post by David T. Lewis

Hi Tobias,

On Fri, Nov 21, 2014 at 4:51 AM, Tobias Pape <[hidden email]> wrote:

Hi,

On 21.11.2014, at 13:44, Bert Freudenberg <[hidden email]> wrote:

> On 21.11.2014, at 13:29, J. Vuletich (mail lists) <[hidden email]> wrote:
>
>> Quoting Bert Freudenberg <[hidden email]>:
>>>
>>> I'd suggest BoxedDouble and ImmediateDouble as names for the concrete subclasses (*). Names do mean something. (**)
>>>
>>> You're right about the FloatArray confusion. However, note that the IEEE standard calls it single and double. It's only C using "float" to mean "single precision".
>>>
>>> I'd name the abstract superclass Float, for readability, and the isFloat test etc. Also: "Float pi" reads a lot nicer than anything else. I don't see the need for having a deep LimitedPrecisionReal - Float - BoxedDouble/ImmediateDouble deep hierarchy now.
>>>
>>> If we ever add single-precision floats, we should name them BoxedSingle and ImmediateSingle. At that point we might want a Single superclass and a LimitedPrecisionReal supersuperclass, but we can cross that bridge when we get there.
>>>
>>> - Bert -
>>>
>>> (*) Since we're not going to see the class names often, we could even spell it out as BoxedDoublePrecisionFloat and ImmediateDoublePrecisionFloat. Only half joking. It would make the relation to the abstract Float very clear.
>>>
>>> (**) We could also try to make the names googleable. I was surprised to not get a good hit for "boxed immediate". Only "boxed unboxed" finds it. Maybe there are two better words?
>>
>> I very much agree with Bert. But I'd suggest SmallDouble instead of ImmediateDouble for consistency with SmallInteger.
>
> Then it would have to be LargeDouble for consistency with LargeInteger, too. Which I don't find compelling.
>
> Also, with the 64 bit format we get many more immediate objects. There already are immediate integers and characters, floats will be the third, there could be more, like immediate points. For those, the small/large distinction does not make sense.
>
> Maybe Eliot's idea of keeping "Float" in the name was best, but instead of "small" use "immediate":
>
> Float - BoxedFloat - ImmediateFloat
>
> A Float is either a BoxedFloat or an ImmediateFloat, depending on the magnitude of its exponent.

I don't like the idea of putting a VM/Storage detail into the Class name.
The running system itself does not care about whether Floats or Integers are
boxed or immediate.

I disagree. I think at least Smalltalk-80 has a philosophy of lifting as much out of the VM into the system, and hiding it from clients via encapsulation. So unlike many other VMs the compiler is in the system, the system explicitly separates SmallInteger, LargePositiveInteger and LargeNegativeInteger and implements large integer arithmetic with Smalltalk code that uses SmallIntegers. Note that the primitives are an optional extra optimization that the VM does not need to implement. So for me it is in keeping with the current system to use BoxedFloat and SmallFloat or BoxedDouble and SmallDouble.

This lifting things up provides us with an extremely malleable system. Pushing things down into the VM does the opposite.

For example in RSqueakVM (aka SPy) there is no immediate
Integer whatsoever. Yes, tagged ints are read during image startup but they
aren't subsequently represented as immediates or tagged ints after that.

Well because it's implemented above RPython I guess it is using Python's bignum code directly. That's fine but its a bit of a cheat.

Just as input, in the Racket language and other Schemes,
the equivalent to our SmallInterger/LargeInteger is fixnum/bignum
and for floats they have flonums and "extflonums" (80bit).

Best
-Tobias

thanks

best,

Eliot

Tobias Pape

Re: [Vm-dev] Re: [squeak-dev] Float hierarchy for 64-bit Spur

Hi Eliot

On 21.11.2014, at 19:06, Eliot Miranda <[hidden email]> wrote:

>
> Hi Tobias,
>
> On Fri, Nov 21, 2014 at 4:51 AM, Tobias Pape <[hidden email]> wrote:
>
> > Hi,
> >
> > On 21.11.2014, at 13:44, Bert Freudenberg <[hidden email]> wrote:
> >
> > > On 21.11.2014, at 13:29, J. Vuletich (mail lists) <
> > [hidden email]> wrote:
> > >
> > >> Quoting Bert Freudenberg <[hidden email]>:
> > >>>
> > >>> I'd suggest BoxedDouble and ImmediateDouble as names for the concrete
> > subclasses (*). Names do mean something. (**)
> > >>>
> > >>> You're right about the FloatArray confusion. However, note that the
> > IEEE standard calls it single and double. It's only C using "float" to mean
> > "single precision".
> > >>>
> > >>> I'd name the abstract superclass Float, for readability, and the
> > isFloat test etc. Also: "Float pi" reads a lot nicer than anything else. I
> > don't see the need for having a deep LimitedPrecisionReal - Float -
> > BoxedDouble/ImmediateDouble deep hierarchy now.
> > >>>
> > >>> If we ever add single-precision floats, we should name them
> > BoxedSingle and ImmediateSingle. At that point we might want a Single
> > superclass and a LimitedPrecisionReal supersuperclass, but we can cross
> > that bridge when we get there.
> > >>>
> > >>> - Bert -
> > >>>
> > >>> (*) Since we're not going to see the class names often, we could even
> > spell it out as BoxedDoublePrecisionFloat and
> > ImmediateDoublePrecisionFloat. Only half joking. It would make the relation
> > to the abstract Float very clear.
> > >>>
> > >>> (**) We could also try to make the names googleable. I was surprised
> > to not get a good hit for "boxed immediate". Only "boxed unboxed" finds it.
> > Maybe there are two better words?
> > >>
> > >> I very much agree with Bert. But I'd suggest SmallDouble instead of
> > ImmediateDouble for consistency with SmallInteger.
> > >
> > > Then it would have to be LargeDouble for consistency with LargeInteger,
> > too. Which I don't find compelling.
> > >
> > > Also, with the 64 bit format we get many more immediate objects. There
> > already are immediate integers and characters, floats will be the third,
> > there could be more, like immediate points. For those, the small/large
> > distinction does not make sense.
> > >
> > > Maybe Eliot's idea of keeping "Float" in the name was best, but instead
> > of "small" use "immediate":
> > >
> > > Float - BoxedFloat - ImmediateFloat
> > >
> > > A Float is either a BoxedFloat or an ImmediateFloat, depending on
> > the magnitude of its exponent.
> >
> > I don't like the idea of putting a VM/Storage detail into the Class name.
> > The running system itself does not care about whether Floats or Integers
> > are
> > boxed or immediate.
> >
>
> I disagree. I think at least Smalltalk-80 has a philosophy of lifting as
> much out of the VM into the system, and hiding it from clients via
> encapsulation. So unlike many other VMs the compiler is in the system, the
> system explicitly separates SmallInteger, LargePositiveInteger and
> LargeNegativeInteger and implements large integer arithmetic with Smalltalk
> code that uses SmallIntegers. Note that the primitives are an optional
> extra optimization that the VM does not need to implement. So for me it is
> in keeping with the current system to use BoxedFloat and SmallFloat or
> BoxedDouble and SmallDouble.
>
> This lifting things up provides us with an extremely malleable system.
> Pushing things down into the VM does the opposite.
>

I can understand. It is however a tradeoff between abstraction and malleability.
I'd rather see everything done in Smalltalk. Yet primitives not exposing its
innards.

I think I just can't have the cake and have it, too.

>
> For example in RSqueakVM (aka SPy) there is no immediate
> > Integer whatsoever. Yes, tagged ints are read during image startup but they
> > aren't subsequently represented as immediates or tagged ints after that.
> >
>
> Well because it's implemented above RPython I guess it is using Python's
> bignum code directly. That's fine but its a bit of a cheat.

I was talking of SmallInts here. There is no bignum code involved.
On the RPython side, SmallIntegers are just objects that have a field
that is not accessible from Smalltalk but keeps a machine-word integer.

>
>
> >
> > Just as input, in the Racket language and other Schemes,
> > the equivalent to our SmallInterger/LargeInteger is fixnum/bignum
> > and for floats they have flonums and "extflonums" (80bit).
> >
> > Best
> > -Tobias
>
>

Eliot Miranda-2

Re: [Vm-dev] Re: [squeak-dev] Float hierarchy for 64-bit Spur

Hi Tobias,

On Fri, Nov 21, 2014 at 10:52 AM, Tobias Pape <[hidden email]> wrote:

Hi Eliot

On 21.11.2014, at 19:06, Eliot Miranda <[hidden email]> wrote:
>
> Hi Tobias,
>
> On Fri, Nov 21, 2014 at 4:51 AM, Tobias Pape <[hidden email]> wrote:
>
> > Hi,
> >
> > On 21.11.2014, at 13:44, Bert Freudenberg <[hidden email]> wrote:
> >
> > > On 21.11.2014, at 13:29, J. Vuletich (mail lists) <
> > [hidden email]> wrote:
> > >
> > >> Quoting Bert Freudenberg <[hidden email]>:
> > >>>
> > >>> I'd suggest BoxedDouble and ImmediateDouble as names for the concrete
> > subclasses (*). Names do mean something. (**)
> > >>>
> > >>> You're right about the FloatArray confusion. However, note that the
> > IEEE standard calls it single and double. It's only C using "float" to mean
> > "single precision".
> > >>>
> > >>> I'd name the abstract superclass Float, for readability, and the
> > isFloat test etc. Also: "Float pi" reads a lot nicer than anything else. I
> > don't see the need for having a deep LimitedPrecisionReal - Float -
> > BoxedDouble/ImmediateDouble deep hierarchy now.
> > >>>
> > >>> If we ever add single-precision floats, we should name them
> > BoxedSingle and ImmediateSingle. At that point we might want a Single
> > superclass and a LimitedPrecisionReal supersuperclass, but we can cross
> > that bridge when we get there.
> > >>>
> > >>> - Bert -
> > >>>
> > >>> (*) Since we're not going to see the class names often, we could even
> > spell it out as BoxedDoublePrecisionFloat and
> > ImmediateDoublePrecisionFloat. Only half joking. It would make the relation
> > to the abstract Float very clear.
> > >>>
> > >>> (**) We could also try to make the names googleable. I was surprised
> > to not get a good hit for "boxed immediate". Only "boxed unboxed" finds it.
> > Maybe there are two better words?
> > >>
> > >> I very much agree with Bert. But I'd suggest SmallDouble instead of
> > ImmediateDouble for consistency with SmallInteger.
> > >
> > > Then it would have to be LargeDouble for consistency with LargeInteger,
> > too. Which I don't find compelling.
> > >
> > > Also, with the 64 bit format we get many more immediate objects. There
> > already are immediate integers and characters, floats will be the third,
> > there could be more, like immediate points. For those, the small/large
> > distinction does not make sense.
> > >
> > > Maybe Eliot's idea of keeping "Float" in the name was best, but instead
> > of "small" use "immediate":
> > >
> > > Float - BoxedFloat - ImmediateFloat
> > >
> > > A Float is either a BoxedFloat or an ImmediateFloat, depending on
> > the magnitude of its exponent.
> >
> > I don't like the idea of putting a VM/Storage detail into the Class name.
> > The running system itself does not care about whether Floats or Integers
> > are
> > boxed or immediate.
> >
>
> I disagree. I think at least Smalltalk-80 has a philosophy of lifting as
> much out of the VM into the system, and hiding it from clients via
> encapsulation. So unlike many other VMs the compiler is in the system, the
> system explicitly separates SmallInteger, LargePositiveInteger and
> LargeNegativeInteger and implements large integer arithmetic with Smalltalk
> code that uses SmallIntegers. Note that the primitives are an optional
> extra optimization that the VM does not need to implement. So for me it is
> in keeping with the current system to use BoxedFloat and SmallFloat or
> BoxedDouble and SmallDouble.
>
> This lifting things up provides us with an extremely malleable system.
> Pushing things down into the VM does the opposite.
>

I can understand. It is however a tradeoff between abstraction and malleability.
I'd rather see everything done in Smalltalk. Yet primitives not exposing its
innards.

I think I just can't have the cake and have it, too.

yes, alas it is all about tradeoffs :-). But that's great. The more varieties the merrier.

>
> For example in RSqueakVM (aka SPy) there is no immediate
> > Integer whatsoever. Yes, tagged ints are read during image startup but they
> > aren't subsequently represented as immediates or tagged ints after that.
> >
>
> Well because it's implemented above RPython I guess it is using Python's
> bignum code directly. That's fine but its a bit of a cheat.

I was talking of SmallInts here. There is no bignum code involved.
On the RPython side, SmallIntegers are just objects that have a field
that is not accessible from Smalltalk but keeps a machine-word integer.

Hmmm, somewhere there's got to be a discrimination between SmallIntegers and other objects, right?

> > Just as input, in the Racket language and other Schemes,
> > the equivalent to our SmallInterger/LargeInteger is fixnum/bignum
> > and for floats they have flonums and "extflonums" (80bit).
> >
> > Best
> > -Tobias

best,

Eliot

Tobias Pape

Re: [Vm-dev] Re: [squeak-dev] Float hierarchy for 64-bit Spur

Hi Eliot

On 21.11.2014, at 19:56, Eliot Miranda <[hidden email]> wrote:

> Hi Tobias,
>
> On Fri, Nov 21, 2014 at 10:52 AM, Tobias Pape <[hidden email]> wrote:
> Hi Eliot
>
> On 21.11.2014, at 19:06, Eliot Miranda <[hidden email]> wrote:
> >
> > Hi Tobias,
> >
> > On Fri, Nov 21, 2014 at 4:51 AM, Tobias Pape <[hidden email]> wrote:
> >
> > > Hi,
> > >
> > > On 21.11.2014, at 13:44, Bert Freudenberg <[hidden email]> wrote:
> > >
> > > > On 21.11.2014, at 13:29, J. Vuletich (mail lists) <
> > > [hidden email]> wrote:
> > > >
> > > >> Quoting Bert Freudenberg <[hidden email]>:
> > > >>>
> > > >>> I'd suggest BoxedDouble and ImmediateDouble as names for the concrete
> > > subclasses (*). Names do mean something. (**)
> > > >>>
> > > >>> You're right about the FloatArray confusion. However, note that the
> > > IEEE standard calls it single and double. It's only C using "float" to mean
> > > "single precision".
> > > >>>
> > > >>> I'd name the abstract superclass Float, for readability, and the
> > > isFloat test etc. Also: "Float pi" reads a lot nicer than anything else. I
> > > don't see the need for having a deep LimitedPrecisionReal - Float -
> > > BoxedDouble/ImmediateDouble deep hierarchy now.
> > > >>>
> > > >>> If we ever add single-precision floats, we should name them
> > > BoxedSingle and ImmediateSingle. At that point we might want a Single
> > > superclass and a LimitedPrecisionReal supersuperclass, but we can cross
> > > that bridge when we get there.
> > > >>>
> > > >>> - Bert -
> > > >>>
> > > >>> (*) Since we're not going to see the class names often, we could even
> > > spell it out as BoxedDoublePrecisionFloat and
> > > ImmediateDoublePrecisionFloat. Only half joking. It would make the relation
> > > to the abstract Float very clear.
> > > >>>
> > > >>> (**) We could also try to make the names googleable. I was surprised
> > > to not get a good hit for "boxed immediate". Only "boxed unboxed" finds it.
> > > Maybe there are two better words?
> > > >>
> > > >> I very much agree with Bert. But I'd suggest SmallDouble instead of
> > > ImmediateDouble for consistency with SmallInteger.
> > > >
> > > > Then it would have to be LargeDouble for consistency with LargeInteger,
> > > too. Which I don't find compelling.
> > > >
> > > > Also, with the 64 bit format we get many more immediate objects. There
> > > already are immediate integers and characters, floats will be the third,
> > > there could be more, like immediate points. For those, the small/large
> > > distinction does not make sense.
> > > >
> > > > Maybe Eliot's idea of keeping "Float" in the name was best, but instead
> > > of "small" use "immediate":
> > > >
> > > > Float - BoxedFloat - ImmediateFloat
> > > >
> > > > A Float is either a BoxedFloat or an ImmediateFloat, depending on
> > > the magnitude of its exponent.
> > >
> > > I don't like the idea of putting a VM/Storage detail into the Class name.
> > > The running system itself does not care about whether Floats or Integers
> > > are
> > > boxed or immediate.
> > >
> >
> > I disagree. I think at least Smalltalk-80 has a philosophy of lifting as
> > much out of the VM into the system, and hiding it from clients via
> > encapsulation. So unlike many other VMs the compiler is in the system, the
> > system explicitly separates SmallInteger, LargePositiveInteger and
> > LargeNegativeInteger and implements large integer arithmetic with Smalltalk
> > code that uses SmallIntegers. Note that the primitives are an optional
> > extra optimization that the VM does not need to implement. So for me it is
> > in keeping with the current system to use BoxedFloat and SmallFloat or
> > BoxedDouble and SmallDouble.
> >
> > This lifting things up provides us with an extremely malleable system.
> > Pushing things down into the VM does the opposite.
> >
>>
>> I can understand. It is however a tradeoff between abstraction and malleability.
>> I'd rather see everything done in Smalltalk. Yet primitives not exposing its
>> innards.
>>
>> I think I just can't have the cake and have it, too.
>>
> yes, alas it is all about tradeoffs :-). But that's great. The more varieties the merrier.
>
>
> >
> > For example in RSqueakVM (aka SPy) there is no immediate
> > > Integer whatsoever. Yes, tagged ints are read during image startup but they
> > > aren't subsequently represented as immediates or tagged ints after that.
> > >
> >
> > Well because it's implemented above RPython I guess it is using Python's
> > bignum code directly. That's fine but its a bit of a cheat.
>>
>> I was talking of SmallInts here. There is no bignum code involved.
>> On the RPython side, SmallIntegers are just objects that have a field
>> that is not accessible from Smalltalk but keeps a machine-word integer.
>>
> Hmmm, somewhere there's got to be a discrimination between SmallIntegers and other objects, right?

It is done. They are just objects but object identity is delegated to
value identity [1]. All primitives know about this and they unwrap
and rewrap the boxed machine int. It's just a straight-forward boxed
implementation of integers. Where have I confused you?

>
> > > Just as input, in the Racket language and other Schemes,
> > > the equivalent to our SmallInterger/LargeInteger is fixnum/bignum
> > > and for floats they have flonums and "extflonums" (80bit).
> > >
> > > Best
> > > -Tobias

Best
-Tobias

[1]: https://bitbucket.org/pypy/lang-smalltalk/src/2a99a4827c84352bbd8344a327937c4c9fdf9c33/spyvm/model.py?at=default#cl-249

stepharo

Re: Float hierarchy for 64-bit Spur

In reply to this post by Eliot Miranda-2

Le 21/11/14 02:51, Eliot Miranda a écrit :

Hi All,

64-bit Spur can usefully provide an immediate float, a 61-bit subset of the ieee double precision float. The scheme steals bits from the mantissa to use for the immediate's 3-bit tag pattern. So values have the same precision as ieee doubles, but can only represent the subset with exponents between 10^-38 and 10^38, the single-precision range. The issue here is how to organize the class hierarchy.

The approach that looks best to me is to modify class Float to be an abstract class, and add two subclasses, BoxedFloat and SmallFloat, such that existing boxed instances of Float outside the SmallFloat range will become instances of BoxedFloat and instances within that range will be replaced by references to the relevant SmallFloat.

With this approach ...

- Float pi etc can still be used, even though they will answer instances of SmallFloat. But tests such as "self assert: result class == Float." will need to be rewritten to e.g. "self assert: result isFloat".

- BoxedFloat and SmallFloat will not be mentioned much at all since floats print themselves literally, and so the fact that the classes have changed won't be obvious.

- the boxed Float primitives (receiver is a boxed float) live in BoxedFloat and the immediate ones live in SmallFloat. Making SmallFloat a subclass of Float poses problems for all the primitives that do a super send to retry, since the boxed Float prims will be above the unboxed ones and so the boxed ones would have to test for an immediate receiver.

An alternative, that VW took (because it has both Float and Double) is to add a superclass, e.g. LimitedPrecisionReal, move most of the methods into it, and keep Float as Float, and add SmallFloat as a subclass of LimitedPrecisionReal. Then while class-side methods such as pi would likely be implemented in LimitedPrecisionReal class, sends to Float to access them find them via inheritance. An automatic reorganization which moves only primitives out of LimitedPrecisionReal is easy to write.

Eliot the solution proposed by VM is nice in the sense that we can continue to use Float pi...
On the other hand, I like the design used on objective-c when the superclass act as a factory for its subclass hidding concrete implementation classes.
Now I do not know if his would make sense for Float.
Another point, I do not really like Boxed because this is the first time we use it. May be SmallFloat would be in the same spirit than SmallInteger.

Thoughts?
--

best,
Eliot

Chris Muller-3

Re: [Vm-dev] Re: [squeak-dev] Float hierarchy for 64-bit Spur

In reply to this post by David T. Lewis

> I have always felt that the mapping of Float to 64-bit double and FloatArray
> to 32-bit float is awkward. It may be that 32-bit floats are becoming less
> relevant nowadays, but if short float values are still important, then it

From the sense that a lot of computing is addressing fuzzy pattern
matching, 32-bit speed and space are actually becoming more relevant.

> would be nice to be able to represent them directly. I like the idea of having
> a Float class and a Double class to represent the two most common representations.
> A class hierarchy that could potentially support this sounds like a good idea to me.
>
> I have no experience with VW, but a LimitedPrecisionReal hierachy sounds like a
> reasonable approach.
>
> Dave
>