Re: Division still cost more than multiplication?
- To: mathgroup at smc.vnet.net
- Subject: [mg24304] Re: Division still cost more than multiplication?
- From: AES <siegman at stanford.edu>
- Date: Fri, 7 Jul 2000 00:11:46 -0400 (EDT)
- Organization: Stanford University
- References: <8k0tc4$q2o@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
In article <8k0tc4$q2o at smc.vnet.net>, AES <siegman at stanford.edu> wrote:
> Old-time FORTRAN programmers (like me) were taught (at least in early
> days) that division cost a lot more machine cycles than multiplication.
> So, if you had an expression like y = x/c that was going to be called
> many times inside a loop, where x and y were variables and c a constant,
> you'd code this as:
[snip]
> Does this still make any sense in Mathematica? Or is it a primitive
> relic of long-gone days?
+++++++++++++++++++++++++++++++++++++++++++++
Anticipating replies to my query that I believe are coming from P. J.
Hinton and Daniel Lichtbau ((thanks to both), here is the same test as
P. J. Hintons, performed on a 1998-model 400 MHz Mac PowerBook G3,
giving very similar results:
In[7]:= {num, den} = {Random[], Random[]}
Out[7]= {0.0991313, 0.0559147}
In[8]:= recip = 1.0 / den
Out[8]= 17.8844
In[9]:= Timing[Do[num/den, {2000000}]]
Out[9]= {28.8 Second, Null}
In[10]:= {num, den} = {Random[], Random[]}
Out[10]= {0.132828, 0.28853}
In[11]:= recip = 1.0 / den
Out[11]= 3.46585
In[12]:= Timing[Do[num * recip, {2000000}]]
Out[12]= {14.6833 Second, Null}