[squeak-dev] FloatConstants?

Levente Uzonyi leves at elte.hu
Tue Dec 23 23:52:29 UTC 2014


I don't know how you measured the speedup, but I got 8-12x improvement for 
finite numbers. By creating a new FloatArray, the speedup decreases to 
6-9x.

Levente

On Tue, 23 Dec 2014, Chris Muller wrote:

> On Mon, Dec 22, 2014 at 3:59 AM, Bert Freudenberg <bert at freudenbergs.de> wrote:
>> On 22.12.2014, at 00:13, Levente Uzonyi <leves at elte.hu> wrote:
>>>
>>> ConverterFloatArray at: 1 put: self; basicAt: 1.
>>
>> Any reason not to use this in #asIEEE32BitWord? Endianness? Arch-dependency?
>>
>> I see, it's not thread-safe. This would be:
>>
>>         (FloatArray new: 1) at: 1 put: self; basicAt: 1.
>>
>> Might still be faster?
>
> Yes.  Since creation of a one-element FloatArray every time did not
> adversely affect performance of Levente's too significantly (only 3.7X
> instead of 4.0X faster), I decided it was worth the cost of the
> allocation than to worry about concurrency.  So I ended up with
> Levente's latest except I cannot risk a calculation ending up -0.0, so
> I have to account for it too.  And, NaN too.  Thus:
>
>     hashKey32
>          | bits |
>          self = NegativeInfinity ifTrue: [ ^ 0 ].
>          self = Infinity ifTrue: [ ^ 4294967294 ].
>          self = NaN ifTrue: [ ^ 4294967295 ].
>          self = NegativeZero ifTrue: [ ^ 2147483651 ].
>          bits := (FloatArray new: 1) at: 1 put: self; basicAt: 1.
>          self < 0.0 ifTrue: [ ^ 4286578688 - bits ].
>          ^ 2147483651 + bits
>
> Since there are not a full 32-bits worth of IEEE 32-bit floats (e.g.,
> several thousand convert to NaN), it might be wise to move +Infinity
> and NaN _down_ a bit from the very maximum, for better continuity
> between the float and integer number lines, or for potential future
> special-case needs..?
>
> In any case, I wanted to at least see if what we have, above, works
> for every 32-bit IEEE float.  To verify that, I enumerated all Floats
> in numerical order from -Infinity to +Infinity by creating them via
> #fromIEEE32BitFloat: from the appropriate ranges.
>
> It hit a snag at 2151677948.  Check this out:
>
>     | this next |
>     this := Float fromIEEE32Bit: 2151677949.
>     next := Float fromIEEE32Bit: 2151677948.
>     self
>          assert: next > this ;
>          assert: ((FloatArray new: 1) at: 1 put: (next); basicAt: 1)
>> ((FloatArray new: 1) at: 1 put: (this); basicAt: 1)
>
> As I thought, the representations between IEEE floats and FloatArray
> floats are different-enough that their precisions align differently
> onto the 32-bit map for these two floats.  IEEE's are precise-enough
> to distinguish these two floats, FloatArray representations are not.
>
> That these guys are considered "equal" by the FloatArray is actually
> good enough for my indexing requirement, but now I'm looking at the
> prim-fail code for FloatArray:
>
>    at: index
>         <primitive: 'primitiveAt' module: 'FloatArrayPlugin'>
>          ^Float fromIEEE32Bit: (self basicAt: index)
>
> If this or the #at:put: primitive were to ever fail on the storage
> (at:put:) exclusive-or the access (at:) side, then it appears
> FloatArray itself would retrieve a value different than was stored..!
>
>


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