Re: [PATCH v2 08/17] virstring: Introduce virStringIsNull()
On Tue, Jul 07, 2020 at 21:46:26 +0200, Michal Privoznik wrote:
This function will be used to detect zero buffers (which are
going to be interpreted as hole in virStream later).
I shamelessly took inspiration from coreutils.
Coreutils is proudly GPLv3 ...
Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com>
---
src/libvirt_private.syms | 1 +
src/util/virstring.c | 38 ++++++++++++++++++++++++++++++++
src/util/virstring.h | 2 ++
tests/virstringtest.c | 47 ++++++++++++++++++++++++++++++++++++++++
4 files changed, 88 insertions(+)
[...]
diff --git a/src/util/virstring.c b/src/util/virstring.c
index e9e792f3bf..c26bc770d4 100644
--- a/src/util/virstring.c
+++ b/src/util/virstring.c
@@ -1404,3 +1404,41 @@ int virStringParseYesNo(const char *str, bool *result)
return 0;
}
+
+
+/**
+ * virStringIsNull:
IsNull might indicate that this does a check if the pointer is NULL. You
are checking for NUL bytes.
+ * @buf: buffer to check
+ * @len: the length of the buffer
+ *
+ * For given buffer @buf and its size @len determine whether
+ * it contains only zero bytes (NUL) or not.
Given the semantics of C strings being terminated by the NUL byte I
don't think this function qualifies as a string helper and thus should
probably reside somewhere outside of virstring.h
+ *
+ * Returns: true if buffer is full of zero bytes,
+ * false otherwise.
+ */
+bool virStringIsNull(const char *buf, size_t len)
+{
+ const char *p = buf;
+
+ if (!len)
+ return true;
+
+ /* Check up to 16 first bytes. */
+ for (;;) {
+ if (*p)
+ return false;
+
+ p++;
+ len--;
+
+ if (!len)
+ return true;
+
+ if ((len & 0xf) == 0)
+ break;
+ }
Do we really need to do this optimization? We could arguably simplify
this to:
if (*buf != '\0')
return false;
return memcmp(buf, buf + 1, len - 1);
You can then use the saved lines to explain that comparing a piece of
memory with itself shifted by any position just ensures that there are
repeating sequences of itself in the remainder and by shifting it by 1
it means that it checks that the strings are just the same byte. The
check above then ensuers that the one byte is NUL.