[Qemu-devel] [PATCH v5 07/10] xbzrle: don't check the value in the vm ram repeatedly

[arei.gonglei]

From: ChenLiang <address@hidden>

xbzrle_encode_buffer checks the value in the vm ram repeatedly.
It is risk if runs xbzrle_encode_buffer on changing data.
And it is not necessary.

Reported-by: Dr. David Alan Gilbert <address@hidden>
Signed-off-by: ChenLiang <address@hidden>
Signed-off-by: Gonglei <address@hidden>
---
 xbzrle.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/xbzrle.c b/xbzrle.c
index fbcb35d..92cccd7 100644
--- a/xbzrle.c
+++ b/xbzrle.c
@@ -27,9 +27,10 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, 
int slen,
                          uint8_t *dst, int dlen)
 {
     uint32_t zrun_len = 0, nzrun_len = 0;
-    int d = 0, i = 0;
+    int d = 0, i = 0, j;
     long res, xor;
     uint8_t *nzrun_start = NULL;
+    uint8_t *xor_ptr = (uint8_t *)(&xor);
 
     g_assert(!(((uintptr_t)old_buf | (uintptr_t)new_buf | slen) %
                sizeof(long)));
@@ -82,6 +83,8 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, 
int slen,
         if (d + 2 > dlen) {
             return -1;
         }
+        i++;
+        nzrun_len++;
         /* not aligned to sizeof(long) */
         res = (slen - i) % sizeof(long);
         while (res && old_buf[i] != new_buf[i]) {
@@ -98,11 +101,16 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t 
*new_buf, int slen,
                 xor = *(long *)(old_buf + i) ^ *(long *)(new_buf + i);
                 if ((xor - mask) & ~xor & (mask << 7)) {
                     /* found the end of an nzrun within the current long */
-                    while (old_buf[i] != new_buf[i]) {
-                        nzrun_len++;
-                        i++;
+                    for (j = 0; j < sizeof(long); j++) {
+                        if (0 == xor_ptr[j]) {
+                            break;
+                        }
+                    }
+                    i += j;
+                    nzrun_len += j;
+                    if (j != sizeof(long)) {
+                        break;
                     }
-                    break;
                 } else {
                     i += sizeof(long);
                     nzrun_len += sizeof(long);
@@ -118,6 +126,8 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t 
*new_buf, int slen,
         memcpy(dst + d, nzrun_start, nzrun_len);
         d += nzrun_len;
         nzrun_len = 0;
+        i++;
+        zrun_len++;
     }
 
     return d;
-- 
1.7.12.4