Re: [pooma-dev] RFA: delete_test1 Modifications

[Jeffrey Oldham]

For those skipping intermediary emails, the discussion is whether
memmove() is faster than copy().

Attached is a program that constructs a vector, copies its contents to
another vector, and then checks the copy for correctness.  On
Linux/gcc3.0 and Irix6.5/KCC, I cannot find any significant speed
difference between std::copy and std::memmove for vectors of doubles.
Given this result, may we use std::copy() everywhere since it is
guaranteed to compile?

Thanks,
Jeffrey D. Oldham
address@hidden


On Thu, May 24, 2001 at 09:49:24AM -0700, James Crotinger wrote:
> Actually, I think "fast code" is one of our prime directives. We should try
> to find a way to do both. 
> 
>   Jim
> 
> > -----Original Message-----
> > From: Jeffrey Oldham [mailto:address@hidden
> > Sent: Thursday, May 24, 2001 10:46 AM
> > To: James Crotinger
> > Cc: address@hidden
> > Subject: Re: [pooma-dev] RFA: delete_test1 Modifications
> > 
> > 
> > On Thu, May 24, 2001 at 09:33:45AM -0700, James Crotinger wrote:
> > > The memmove optimization was fairly substantial when I 
> > tested it. I think it
> > > would be better to modify the code to pass addresses to 
> > memmove - again this
> > > gets to the question of whether it is really OK to use 
> > &a.begin()[0] to be
> > > the address of the 0th element, etc.
> > 
> > Yes, I imagine that memmove() is significantly faster than copy(), but
> > I would prefer to have code that is guaranteed to compile rather than
> > fast code that compiles only for certain platforms.
> > 
> > > > -----Original Message-----
> > > > From: Jeffrey Oldham [mailto:address@hidden
> > > > Sent: Wednesday, May 23, 2001 6:33 PM
> > > > To: address@hidden
> > > > Subject: [pooma-dev] RFA: delete_test1 Modifications
> > > > 
> > > > 
> > > > OK to commit?
> > > > 
> > > > Compiling src/Utilities/tests/delete_test1.cpp showed 
> > that the vector
> > > > type `Array_t' was declared to store doubles but actually stored
> > > > integers.  Also, a call to std::memmove() illegally 
> > converted vector
> > > > iterators to pointers.  The alternative call to 
> > std::copy() is instead
> > > > used.
> > > > 
> > > > 2001 May 23  Jeffrey D. Oldham  <address@hidden>
> > > > 
> > > >         * delete_test1.cpp (Array_t): s/vector<double>/vector<int>/
> > > >         (delete_shiftup_test2): Remove "optimization" call to memmove.
> > > > 
> > > > Tested on       sequential Linux using gcc 3.0 by compiling the program
> > > > Approved by     ???you???
> > 
> > Thanks,
> > Jeffrey D. Oldham
> > address@hidden
> > 

-- 
Jeffrey D. Oldham
address@hidden

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