[Numpy-discussion] Re: numpy, overflow, inf, ieee, and rich , comparison

[Huaiyu Zhu]

On Thu, 26 Oct 2000 07:16:06 GMT, Donald O'Donnell <donod at home.com> wrote:
>
>What I think some people are loosing sight of, is that the 
>underlying hardware instruction set of most computers 
>contains an integer division instruction which results in a
>quotient and a remainder (which, BTW Alex, implies that it 
>doesn't cost any more to get both even if all you want is just
>the quotient or just the remainder), which is usually at least 
>an order of magnitude faster than a hardware floating point 
>division; and on some computers which lack floating point 
>hardware, a software generated floating point result could 
>take several orders of magnitude longer to compute.  
>
>The compiled C code underlying a Python integer division makes 
>use of this fast hardware integer division instruction.  If 
>Python were changed so that all integer divisions were done in
>floating point, we would loose the ability to make use of this 
>fast hardware divide instruction.  This could have a severe 
>negative impact on some compute intensive (Numpy?) programs.


A little test result.  Doing a+a one million times takes 2.05sec for a==2.2,
and 1.82sec for a==22.  That's about 9/8 ratio.

For a/a the time ratio becomes 2.180/ 2.040, or about 16/15.

Doesn't look like an order of magnitude to me.

Huaiyu

-- 
from profile import run
from operator import div
def test(a):map(div, a, a)
a = [22]*1000000; run("test(a)")
a = [2.2]*1000000; run("test(a)")