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[amibroker] Re: AFL floating point number representation?



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I have been thinking about this, since I started mulling over how to 
design a PowerBackTester

I will only have to read/write 3 core metrics, in and out of memory 
(all other BT metrics can be calc from them on the fly).

I have price = 1.0277 (2.77 %)
plus in and out time (either datenum or timenum etc depending on base 
timeframe).

I might also need to store additional data with the trades e.g. RSI 
value for ranking signals.

For warp speed I am wondering how to get 3 or more units of data in 
one memory series .... I wonder if it would be quicker keep all the 
data that belongs to one trade together and thenunpack the serial 
data, in RAM, into 3 the or more arrays required i.e. the collection 
of arrays that make up the trade matrix?

Don't know anything about bit consumption per integer etc or 
progamming/computers.

I keep coming back to the idea of making 2 * 32 bits operate like a 
pseudo 64 bits (and onwards)?

Anyone heard of this ... it's probably standard computer practise or 
maybe a crazy idea?




 --- In amibroker@xxxxxxxxxxxxxxx, Dennis Brown <see3d@xxx> wrote:
>
> How many bits are your numbers?
> 
> Two 11 bit integers can be be packed and unpacked from one 32 bit  
> float number with ease.  You just mask (&) bits to extract the low  
> order number.  Use multiply or divide to shift the low to the high  
> half of the number and back to the low half again.  Simple bit  
> arithmetic.
> 
> Though it seems there should be easier ways to get what you want.  
I  
> am not a CBT user though.
> 
> BR,
> Dennis
> 
> 
> On Feb 7, 2009, at 7:57 PM, hydroblue@xxx wrote:
> 
> > Thanks Tomasz. I'm looking for a clever way to stuff two numbers 
into
> > the 32 bit float and then later extract the 2 numbers.
> >
> > // fraction = 23 bit integer
> > // exponent = 8 bit integer
> >
> > The reason for doing this is to efficiently get an extra array of
> > numbers into the portfolio backtester without thousands of static 
vars
> > or Foreign symbols.
> >
> > Is there a way to do this in AFL without writing a DLL?
> >
> > --- In amibroker@xxxxxxxxxxxxxxx, "Tomasz Janeczko" <groups@>  
> > wrote:
> >>
> >> Hello,
> >>
> >> IEEE 754 Standard floating point (32 bit, single precision)
> >> http://en.wikipedia.org/wiki/IEEE_754-1985
> >>
> >> Best regards,
> >> Tomasz Janeczko
> >> amibroker.com
> >> ----- Original Message -----
> >> From: <hydroblue@>
> >> To: <amibroker@xxxxxxxxxxxxxxx>
> >> Sent: Saturday, February 07, 2009 5:13 PM
> >> Subject: [amibroker] AFL floating point number representation?
> >>
> >>
> >>> I need to know what range of values and what precision can be
> >>> represented in the AFL floating point arrays, specifically the
> >>> PositionSize array.
> >>>
> >>> It would also be useful to know how many bits are available in 
the
> >>> mantissa and exponent. Any help appreciated.
> >>>
> >>> Thanks,
> >>> Steve
> >>>
> >>>
> >>>
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------------------------------------

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