There is a brand new patch
that speeds up repeated calls to unshift
by a very large
margin. This came out of the PerlMonks conversation at
japhy looks at av.c (not av.h)
, and my original interest in this came out of
a chatter conversation some time ago.
What I find particularly amusing is that this patch is
based on making unshift bigger, slower, and wasteful
of memory. Optimizations are certainly not always obvious!
The way it works is that when you call unshift and it
needs to extend your array, it adds to the request the
size of the current array. The reason is that extending
the array at the front involves moving the whole thing,
and this is expensive so you want to do it as seldom as
possible. In big-O notation with this change
push @foo, 1 for 1..$n;
takes O(n) instead of O(n*n). :-)
The patch has been accepted.
It is in the current development snapshot.