[DUG] Int64 or floating point faster?

[Pieter De Wit]

Hi, 

No, it appears I was wrong. 

Delphi (at least pascal and by default, I assume then delphi) stores
"real"'s as per the IEEE std. 

See :
https://www.informatik.uni-hamburg.de/RZ/software/SUNWspro/pascal/lang_ref/ref_data.doc.html


It's a weird layout which results in (if I understand this correctly) a
multiply instruction to even set the value: 

A real number is represented by this form: 

(-1)sign * 2 exponent-bias *1.f
f is the bits in the fraction 

I would hate to work out the CPU cycles needed to multiply real's... 

Either way - you going to end up with a LOT more CPU usage multiplying
real's vs int - *unless* you need a real, stick to int :) 

A tip from me - I would load the source ints into a few arrays and then
use threading to make it faster/use more cores. 

(This did spark off a talk about if Intel/AMD include a math co-pro with
each core - if not, you really have to stick to threaded int64 - even
more so if your CPUs are hyperthreaded, then you need int64 as a single
core serves 2 HT cores - research the early days of HT for more info on
this :) ) 

Cheers, 

Pieter 

On 17/08/2014 20:09, Cameron Hart wrote: 

> I'm confused now as I'm pretty sure Delphi uses a standard format to represent float (the same format used anywhere else for that matter). In which case a float is essentially two int32 (or other int's depending on the scale of the float). Ie a single used two int16. 
> 
> One int represented the mantissa the other the exponent (in essence the decimal portion). Together they resulted in the floating point value. 
> 
> How would you describe this otherwise? 
> 
> FROM: delphi-bounces at listserver.123.net.nz [mailto:delphi-bounces at listserver.123.net.nz] ON BEHALF OF Jolyon Smith
> SENT: Sunday, 17 August 2014 12:54 p.m.
> TO: NZ Borland Developers Group - Delphi List
> SUBJECT: Re: [DUG] Int64 or floating point faster? 
> 
> That's curious. Who are "they" ? It doesn't sound like any floating point implementation I ever came across in Delphi (or anywhere else, for that matter). O.o 
> 
> On 17 August 2014 12:28, Pieter De Wit <pieter at insync.za.net> wrote: 
> 
> Hi Jolyon,
> 
> From memory, they used 2 int32's to make a float - this could have been int16's - memory is very vague on this :) The one was used to represent the whole numbers and the other was to show the decimal numbers
> 
> Cheers,
> 
> Pieter 
> 
> On 17/08/2014 12:05, Jolyon Smith wrote: 
> 
> @Pieter - I don't understand what you mean when you say that "float was int32.int32". For starters, "float" is an imprecise term. If you mean "single" then the entire value was always 32 bit in it's entirety. If you mean double then it was always 64 bit. What is this "in32.int32" type of which you speak ? O.o 
> 
> On 17 August 2014 11:52, Jolyon Smith <jsmith at deltics.co.nz> wrote: 
> 
> I think there are too many variables involved to give an answer to this question without some of those variables being reduced to known values.
> 
> e.g. what hardware ? what version of Delphi ? x64 target or x86 ? what precision of floating point ?
> 
> Having said that, in a quick test knocked up in my Smoketest framework I found that Double comfortably outperforms Int64 when compiling for Win32 but that both Double and Int64 demonstrated improved performance when compiling for Win64 and that whilst Double still showed some advantage it was not as significant (and in some test runs the difference was negligible).
> 
> If you are targeting FireMonkey you will have to bear in mind that the back-end compiler is different to the x86/x64 backend, so results obtained using the WinXX compilers will not necessarily be indicative of performance on the ARM or LLVM platforms. 
> 
> Conditions: 
> 
> - Delphi XE4 
> 
> - Running in a 64-bit Win 7 VM 
> 
> - No testing was done for correctness of the results. 
> 
> On 16 August 2014 15:30, Ross Levis <ross at stationplaylist.com> wrote: 
> 
> Would I be correct that int64 multiplications would be faster than floating point in Delphi? My app needs to do several million. 
> 
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