To: djgpp AT delorie DOT com
Subject: Re: floating point is... fast???
Message-ID: <19970120.094829.4983.1.chambersb@juno.com>
References: <5brd2e$dap AT lyra DOT csx DOT cam DOT ac DOT uk>
	<32E2D80E DOT 7760 AT gbrmpa DOT gov DOT au>
From: chambersb AT juno DOT com (Benjamin D Chambers)
Date: Mon, 20 Jan 1997 12:49:20 EST


On Mon, 20 Jan 1997 10:27:26 +0800 Leath Muller <leathm AT gbrmpa DOT gov DOT au>
writes:
>> while using the profiler on some code i had written i noticed that 
>changing a
>> floating point multiply to an unsigned multiply of 2 longs turned 
>out to be
>> slower. in fact floating point multiply appears to be faster than 
>ordinary
>> integer multiply for any case. is this actually true? and if so is 
>there any
>> reason i shouldn't just change every multiply in my code to make 
>sure it's
>> floating point?
>
>Yes, floating point is faster because imul and idiv use the floating
>point unit to do the operations - thus an integer mul/divide has the
>overhead of converting the int -> float, div/mul, then float -> int.
>Whereas the floating point calculations just do the div/mul...
>
>Leathal.

If this were true, I couldn't do ANY multiplication/division on my
computer, since I have no FPU (I'm not counting Emulators here).
The integer mul/div routines are so slow precisely *because* they do not
use the FPU - they use the integer unit, which was not made for
mul/div's.

...Chambers
>