What does this warning mean: "DLL attempted to change FPU control word from 8001f to 9001f"

There's a note on this issue at
http://www.nag.co.uk/numeric/RunderWindows.asp 

which claims it can 'safely be ignored'. 

Your mileage may vary, I presume. 

I had the same error message under a previous version (but with a
different library and during installation, not loading, some packages)
and never observed a visible problem. However, I'd be more than willing
to accept that one would not notice changes to FPU precision for many
applications; core R authors seem to have chosen algorithms that are not
badly affected by limited precision. That doesn't mean it would have no
effect for any application, though.

S

Duncan Murdoch <murdoch.duncan at gmail.com> 14/05/2010 22:55 >>>

I started a brand new session in R 2.10.1 (on Windows).
If it matters, I am running the community edition of MySQL 5.0.67,

and it is

all running fine.

I am just beginning to examine the process of getting timer series

data from

one table in MySQL, computing moving averages and computing a

selection of

estimates based on relations among moving averages of different

variates,

and storing all the results in another table in MySQL.

The very first thing I did in this session was execute the following

two

commands:

Sys.setenv(MYSQL_HOME='c:/MySQL')
library(RMySQL)

The output I got was:

Loading required package: DBI
Warning message:
In inDL(x, as.logical(local), as.logical(now), ...) :
  DLL attempted to change FPU control word from 8001f to 9001f

Now, I write programs in relatively high level languages (C++, perl,

Java,

and now R), and NEVER even consider twiddling with FPU control words

or

playing with registers on the processor.  I have never gotten this

close to

the hardware since I messed with video memory in the old days when I

wrote

computer based teaching materials on DOS and had to get acceptable
performance out of the hardware available way back then.. 

Consequently, I

have no idea what this warning means or what I ought to do about it. 

I

assume the DLL it is referring to is

libmySQL.dll<http://www.stat.berkeley.edu/classes/s133/libmySQL.dll>,

which RMySQL needs.  But I have no idea either why it would do what R

says

it is doing or why it matters to me, or what I ought to do about it.

I'd appreciate any info you can provide.

That message means that the RMySQL libraries are trying to mess with
the 
precision of the computations in the rest of your session.    It might

be safe; R fixes the first attempt.  But if the libraries try again, R

won't fix them, and the rest of your computations will be less accurate

than they should be.  It's probably not safe to ignore the warning.   
(This might be unintentional; many Microsoft libraries do this.  But it

is unsafe to use them.)

The safe advice is to recompile the relevant libraries in an
environment 
that doesn't mess with things that don't belong to it.  If this is 
impractical, another safe alternative is to just stop using that 
package.  If this is also impractical, then you should expect your 
computations in R to be less accurate than they should be, and you 
should complain to the supplier of the badly written library that
causes 
the problems.

Duncan Murdoch

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