[DUG] Int64 or floating point faster?

[Ross Levis]

Single precision would be adequate for what I need.  I didn’t explain it very clearly.  My current calculation is like this.

 

Var64bit := Var16bit * Var32bitB div Var32bitC;

If Var64bit > 32767 then Var64bit := 32767;

If Var64bit < -32768 then Var64bit := -32768;

Var16bit := Var64bit;

 

I made the target Int64 since Var16bit * Var32bitB can end up bigger than an Int32 number.  I believe that forces the compiler to use In64 multiplication.  Or perhaps this has the same effect...

 

Var32bitA := Int64(Var16bit * Var32bitB) div Var32bitC;

 

The alternative is to store (Var32bitB / Var32bitC) in a Single var.

 

I suppose I should do my own tests if the speed is not so obvious.

 

Ross.

 

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 11:52 a.m.
To: NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Int64 or floating point faster?

 

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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