Don Stewart wrote:
andrewcoppin:
(Apparently the library isn't 100% complete as yet.)
Right, we haven't bothered with streaming versions of 'words'.
However, the maximumBy and map happily fuse into a single loop.
Indeed. And hopefully when words gets implemented, we will have One Loop
to rule them all... er... well you know what I mean.
Hmm, perhaps to really show this off, we need a more complicated
program. Something that would be just too hard to implement as 1 loop in
C, but is easy for the GHC optimiser to build. I shall meditate on this
further...
Do you have the single loop C program, btw? I'd be curious to see if
this is really "feasible". It would have to do the buffering, tokenising
and accumulating in one go. I'd imagine it is a bit hairy.
And, it should not significantly outperform, say, a bytestring version.
If it does, I'd like to see that.
First version:
n = 0;
while( n < FILE_SIZE )
{
while( n < FILE_SIZE && file[n++] == ' ' ); wStart = n;
while( n < FILE_SIZE && file[n++] != ' ' ); wLength = n - wStart;
if( wLength > strlen( longestString ) ) strncpy( longestString , file
+ wStart , wLength );
}
Takes 0.016 seconds to process a 2.4 MB file. [But not the same one Don
used.]
Then Mr C++ looked at it and said "OMG! You don't *never* use strlen()
inside a loop!" and the second version was writting:
file[FILE_SIZE] = ' ';
n = 0;
maxLength = 0;
while( n < FILE_SIZE )
{
while( file[n++] == ' ' ); wStart = n;
while( file[n++] != ' ' ); wLength = n - wStart;
if( wLength > maxLength )
{
longestWordStart = wStart;
maxLength = wLength;
}
}
strncpy( longestString , file + longestWordStart , maxLength );
This version takes 0.005 seconds.
I have no idea what kind of hardware this is running on - or even which
compiler or OS.
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