On 11/05/2013 10:13 AM, David Cohen wrote:
On 11/05/2013 07:41 AM, Alan Stern wrote:
On Tue, 5 Nov 2013, David Cohen wrote:
+static inline size_t usb_ep_align_maxpacketsize(struct usb_ep *ep, size_t len)
+{
+ int aligned;
+
+ if (ep->desc->bmAttributes & USB_ENDPOINT_XFER_INT)
+ /*
+ * Interrupt eps don't need max packet size to be power of 2,
+ * so can't use cheap IS_ALIGNED() macro.
+ */
+ aligned = !(len % ep->desc->wMaxPacketSize);
+ else
+ aligned = IS_ALIGNED(len, ep->desc->wMaxPacketSize);
This isn't on a hot path, and I suspect that the extra "if" will
require nearly as much time as you save by not doing the division. You
might as well always use the % operation.
Perhaps if I use unlikely() on 'if' condition instead?
Anyway I'll double check the costs of if + IS_ALIGNED vs modulo.
You're missing the point. You and I (not to mention anybody who ever
reads this code in the future) have already wasted more time talking
about it and trying to understand it than you will ever save by using
IS_ALIGNED.
The difference to the computer is minimal at best. Make things easier
for the programmers.
I don't see it as complex :)
But I'm fine with your proposal. I can send new patch dropping
IS_ALIGNED() case.
At a second though, it's even better to drop both 'if' cases.
I can just return round_up(...) directly.
Br, David
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