add QSORT

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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/contrib/coccinelle/qsort.cocci b/contrib/coccinelle/qsort.cocci
new file mode 100644 (file)
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 8aab0c30474764b3e71d4e6c0bc66c52218b3d5e..544db2ae658b782ca983a57997a1e6f990751fd2 100644 (file)
--- 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 inline void 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