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[Qemu-devel] [PATCH 3/3] xbzrle.c: Avoid undefined behaviour with signed
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH 3/3] xbzrle.c: Avoid undefined behaviour with signed arithmetic |
Date: |
Fri, 28 Mar 2014 15:12:57 +0000 |
Use unsigned types for doing bitwise arithmetic in the xzbrle
calculations, to avoid undefined behaviour:
xbzrle.c:99:49: runtime error: left shift of 72340172838076673
by 7 places cannot be represented in type 'long'
Signed-off-by: Peter Maydell <address@hidden>
---
xbzrle.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/xbzrle.c b/xbzrle.c
index fbcb35d..8e220bf 100644
--- a/xbzrle.c
+++ b/xbzrle.c
@@ -28,7 +28,7 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf,
int slen,
{
uint32_t zrun_len = 0, nzrun_len = 0;
int d = 0, i = 0;
- long res, xor;
+ long res;
uint8_t *nzrun_start = NULL;
g_assert(!(((uintptr_t)old_buf | (uintptr_t)new_buf | slen) %
@@ -93,9 +93,11 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf,
int slen,
/* word at a time for speed, use of 32-bit long okay */
if (!res) {
/* truncation to 32-bit long okay */
- long mask = (long)0x0101010101010101ULL;
+ unsigned long mask = (unsigned long)0x0101010101010101ULL;
while (i < slen) {
- xor = *(long *)(old_buf + i) ^ *(long *)(new_buf + i);
+ unsigned long xor;
+ xor = *(unsigned long *)(old_buf + i)
+ ^ *(unsigned 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]) {
--
1.9.0