[Qemu-devel] [PATCHv2 3/9] buffer_is_zero: use vector optimizations if possible

[Peter Lieven <pl@kamp.de>]

performance gain on SSE2 is approx. 20-25%. altivec
is not tested. performance for unsigned long arithmetic
is unchanged.

Signed-off-by: Peter Lieven <pl@kamp.de>
---
 util/cutils.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/util/cutils.c b/util/cutils.c
index 857dd7d..00d98fb 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -190,6 +190,13 @@ size_t buffer_find_nonzero_offset(const void *buf, size_t len)
  */
 bool buffer_is_zero(const void *buf, size_t len)
 {
+    /* use vector optimized zero check if possible */
+    if (((uintptr_t) buf) % sizeof(VECTYPE) == 0 
+          && len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
+             * sizeof(VECTYPE)) == 0) {
+        return buffer_find_nonzero_offset(buf, len)==len;
+    }
+
     /*
      * Use long as the biggest available internal data type that fits into the
      * CPU register and unroll the loop to smooth out the effect of memory
-- 
1.7.9.5