[Qemu-devel] [PATCHv4 3/9] buffer_is_zero: use vector optimizations if possible

From: Peter Lieven <pl@kamp.de>
To: qemu-devel@nongnu.org
Cc: quintela@redhat.com, Stefan Hajnoczi <stefanha@gmail.com>,
	Peter Lieven <pl@kamp.de>, Orit Wasserman <owasserm@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: [Qemu-devel] [PATCHv4 3/9] buffer_is_zero: use vector optimizations if possible
Date: Fri, 22 Mar 2013 13:46:04 +0100	[thread overview]
Message-ID: <1363956370-23681-4-git-send-email-pl@kamp.de> (raw)
In-Reply-To: <1363956370-23681-1-git-send-email-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>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 util/cutils.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/util/cutils.c b/util/cutils.c
index 41c627e..0f43c22 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -205,6 +205,11 @@ bool buffer_is_zero(const void *buf, size_t len)
     long d0, d1, d2, d3;
     const long * const data = buf;
 
+    /* use vector optimized zero check if possible */
+    if (can_use_buffer_find_nonzero_offset(buf, len)) {
+        return buffer_find_nonzero_offset(buf, len) == len;
+    }
+
     assert(len % (4 * sizeof(long)) == 0);
     len /= sizeof(long);
 
-- 
1.7.9.5
