[PATCH 1/3] add QSORT

From: René Scharfe <l.s.r@web.de>
Date: Sep 29, 2016, 15:23 UTC
Message-ID: <67bddc37-4ee2-fef0-c852-e32645421e4c@web.de>

Add the macro QSORT, a convenient wrapper for qsort(3) that infers the size of the array elements and supports the convention of initializing empty arrays with a NULL pointer, which we use in some places.

Calling qsort(3) directly with a NULL pointer is undefined -- even with an element count of zero -- and allows the compiler to optimize away any following NULL checks. Using the macro avoids such surprises.

Add a semantic patch as well to demonstrate the macro's usage and to automate the transformation of trivial cases.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 contrib/coccinelle/qsort.cocci | 19 +++++++++++++++++++
 git-compat-util.h              |  8 ++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 contrib/coccinelle/qsort.cocci

diff --git a/contrib/coccinelle/qsort.cocci b/contrib/coccinelle/qsort.cocci
new file mode 100644
index 0000000..a094e7c
--- /dev/null
+++ b/contrib/coccinelle/qsort.cocci
@@ -0,0 +1,19 @@
+@@
+expression base, nmemb, compar;
+@@
+- qsort(base, nmemb, sizeof(*base), compar);
++ QSORT(base, nmemb, compar);
+
+@@
+expression base, nmemb, compar;
+@@
+- qsort(base, nmemb, sizeof(base[0]), compar);
++ QSORT(base, nmemb, compar);
+
+@@
+type T;
+T *base;
+expression nmemb, compar;
+@@
+- qsort(base, nmemb, sizeof(T), compar);
++ QSORT(base, nmemb, compar);
diff --git a/git-compat-util.h b/git-compat-util.h
index 8aab0c3..d7ed137 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -977,6 +977,14 @@ void git_qsort(void *base, size_t nmemb, size_t size,
 #define qsort git_qsort
 #endif
 
+#define QSORT(base, n, compar) sane_qsort((base), (n), sizeof(*(base)), compar)
+static void inline sane_qsort(void *base, size_t nmemb, size_t size,
+			      int(*compar)(const void *, const void *))
+{
+	if (nmemb > 1)
+		qsort(base, nmemb, size, compar);
+}
+
 #ifndef REG_STARTEND
 #error "Git requires REG_STARTEND support. Compile with NO_REGEX=NeedsStartEnd"
 #endif

-- 
2.10.0