Re: circular shift array

In article <N_adnSlUjZ1NczPb4p2dnAA@xxxxxx>,
Richard Heathfield <rjh@xxxxxxxxxxxxxxx> wrote:
An easier way [to deal with circular queues], which doesn't involve
any shifting at all, is to maintain an object whose purpose is to
store the index of the first item. Then you just process the array
as follows:

idx = head;
for(i = 0; i < n; i++)
{
if(idx++ == n) /* idx = (head + i) % n is shorter, but costlier */

I believe you mean "if (++idx == n)" here. (The post-increment
version can be made to work by changing other values, but it is
then not equivalent to the "idx = (head + i) % n" method.)

Or, one could say:

idx = (head + i) % n; /* if (idx++ == n) is faster, but less correct */

which suggests perhaps you are doing premature optimization. :-)

{
idx = 0;
}
proc(arr[idx]);
}

Also, usually one wants to process first, then test ++idx against n.
(Again, "increment before processing" can be made to work, but is
more complicated.)
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