Take into account that the inline wrapper ensures len >= 4.
Use __attribute__((may_alias)) for accesses via non-char pointers.
Avoid using out-of-bounds pointers in loop boundary conditions by
reformulating the 'for' loop as 'if (...) do { ... } while (...)'.
Signed-off-by: Alexander Monakov <amona...@ispras.ru>
Signed-off-by: Mikhail Romanov <mmroma...@ispras.ru>
---
util/bufferiszero.c | 30 +++++++++++-------------------
1 file changed, 11 insertions(+), 19 deletions(-)
diff --git a/util/bufferiszero.c b/util/bufferiszero.c
index d752edd8cc..1f4cbfaea4 100644
--- a/util/bufferiszero.c
+++ b/util/bufferiszero.c
@@ -29,35 +29,27 @@
bool
buffer_is_zero_len_4_plus(const void *buf, size_t len)
{
- if (unlikely(len < 8)) {
- /* For a very small buffer, simply accumulate all the bytes. */
- const unsigned char *p = buf;
- const unsigned char *e = buf + len;
- unsigned char t = 0;
-
- do {
- t |= *p++;
- } while (p < e);
-
- return t == 0;
+ if (unlikely(len <= 8)) {
+ /* Our caller ensures len >= 4. */
+ return (ldl_he_p(buf) | ldl_he_p(buf + len - 4)) == 0;
} else {
- /* Otherwise, use the unaligned memory access functions to
- handle the beginning and end of the buffer, with a couple
+ /* Use unaligned memory access functions to handle
+ the beginning and end of the buffer, with a couple
of loops handling the middle aligned section. */
- uint64_t t = ldq_he_p(buf);
- const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8);
- const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);
+ uint64_t t = ldq_he_p(buf) | ldq_he_p(buf + len - 8);
+ typedef uint64_t uint64_a __attribute__((may_alias));
+ const uint64_a *p = (void *)(((uintptr_t)buf + 8) & -8);
+ const uint64_a *e = (void *)(((uintptr_t)buf + len - 1) & -8);
- for (; p + 8 <= e; p += 8) {
+ if (e - p >= 8) do {
if (t) {
return false;
}
t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
- }
+ } while ((p += 8) <= e - 8);
while (p < e) {
t |= *p++;
}
- t |= ldq_he_p(buf + len - 8);
return t == 0;
}
--
2.32.0
