Am 24.05.2016 um 15:59 schrieb Paolo Bonzini:
On 24/05/2016 15:39, Peter Lieven wrote:
bytes += offset & (align - 1);
offset = offset & ~(align - 1);
Because the low bits have been masked away from offset and added to bytes,
+
+ /* if head and tail fall into the same alignment
+ * we can omit the second read as it would read
+ * the same block again */
+ if ((offset + bytes) & (align - 1) &&
... the first part is just "bytes & (align - 1)"...
+ offset / align == (offset + bytes) / align) {
... and the second part is just "bytes < align" (you can distribute
division over addition because offset / align has no reminder, and
simplify to "0 == bytes / align").
Putting it together, it becomes "bytes > 0 && bytes < align", or even
"bytes < align".
Oh, thanks, and the if block also too complicated. If I am right it should
collapse to:
if (bytes < align) {
qemu_iovec_add(&local_qiov, head_buf + bytes,
align - bytes);
bytes = align;
}
Right?
Thanks,
Peter
