On 30/10/2019 23.16, Ilya Dryomov wrote:

On Wed, Oct 30, 2019 at 9:35 PM Rasmus Villemoes
[off-list ref] wrote:

quoted

On 30/10/2019 17.19, Ilya Dryomov wrote:

quoted

On Thu, Oct 24, 2019 at 11:49 AM David Howells [off-list ref] wrote:

quoted

 /*
- * We use a start+len construction, which provides full use of the
- * allocated memory.
- * -- Florian Coosmann (FGC)
- *
+ * We use head and tail indices that aren't masked off, except at the point of
+ * dereference, but rather they're allowed to wrap naturally.  This means there
+ * isn't a dead spot in the buffer, provided the ring size < INT_MAX.
+ * -- David Howells 2019-09-23.

Hi David,

Is "ring size < INT_MAX" constraint correct?

No. As long as one always uses a[idx % size] to access the array, the
only requirement is that size is representable in an unsigned int. Then
because one also wants to do the % using simple bitmasking, that further
restricts one to sizes that are a power of 2, so the end result is that
the max size is 2^31 (aka INT_MAX+1).

I think the fact that indices are free running and wrap at a power of
two already restricts you to sizes the are a power of two,

Ah, yes, of course. When reducing indices mod n that may already have
been implicitly reduced mod N, N must be a multiple of n for the result
to be well-defined.

Rasmus