From: Peter Lieven <pl@kamp.de>
Date: Fri, 30 Oct 2015 11:09:56 +0000 (+0100)
Subject: buffer: make the Buffer capacity increase in powers of two
X-Git-Tag: qemu-xen-4.8.0-rc1~681^2~19
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=5c10dbb7b577370e86ff459973b06d530c3777cf;p=qemu-xen.git

buffer: make the Buffer capacity increase in powers of two

This makes sure the number of reallocs is in O(log N).

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1446203414-4013-2-git-send-email-kraxel@redhat.com

[ rebased to util/buffer.c ]

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---

diff --git a/util/buffer.c b/util/buffer.c
index cedd055680..7ddd693fa8 100644
--- a/util/buffer.c
+++ b/util/buffer.c
@@ -20,10 +20,13 @@
 
 #include "qemu/buffer.h"
 
+#define BUFFER_MIN_INIT_SIZE 4096
+
 void buffer_reserve(Buffer *buffer, size_t len)
 {
     if ((buffer->capacity - buffer->offset) < len) {
-        buffer->capacity += (len + 1024);
+        buffer->capacity = pow2ceil(buffer->offset + len);
+        buffer->capacity = MAX(buffer->capacity, BUFFER_MIN_INIT_SIZE);
         buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
     }
 }