[DUG] Int64 or floating point faster?

[Ross Levis]

Thanks for that.  I should have added I'm using Delphi 7 so a 32-bit
compiler.  I assume with newer 64-bit compilers an integer is 64 bits by
default?

 

From: delphi-bounces at listserver.123.net.nz
[mailto:delphi-bounces at listserver.123.net.nz] On Behalf Of Pieter De Wit
Sent: Sunday, 17 August 2014 11:04 a.m.
To: delphi at listserver.123.net.nz
Subject: Re: [DUG] Int64 or floating point faster?

 

On 16/08/2014 15:30, Ross Levis 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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Hi,

Back in the good old days, a float was "int32.int32" - I am not sure what
they have done with it since 64bit CPU's came about, but the theory should
stay the same:

int64=64bit=1 clock cycle to move.
The "mul" command is normally 2 or 3 cycles, so worst case, your int64*int64
will be 6 cycle at worst (2 mov's, 3 for mul and 1 mov for the answer -
moving it to your variable)

By comparison, using float *via the x64* will result in at least 18 cycles -
too early on a Sunday to work it out 100% :)

The tricky part, is the floating point CPU in your machine faster than the
x64 - or more optimized for doing this? I don't know but I am willing to bet
that it is not - floating point math has always been slower for me.

HTH,

Pieter

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