add qsort_r and make qsort a wrapper around it

we make qsort a wrapper by providing a wrapper_cmp function that uses
the extra argument as a function pointer. should be optimized to a tail
call on most architectures, as long as it's built with
-fomit-frame-pointer, so the performance impact should be minimal.

to keep the git history clean, for now qsort_r is implemented in qsort.c
and qsort is implemented in qsort_nr.c.  qsort.c also received a few
trivial cleanups, including replacing (*cmp)() calls with cmp().
qsort_nr.c contains only wrapper_cmp and qsort as a qsort_r wrapper
itself.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/stdlib/qsort_nr.c b/src/stdlib/qsort_nr.c
new file mode 100644
index 00000000..efe7ccec
--- /dev/null
+++ b/src/stdlib/qsort_nr.c
@@ -0,0 +1,14 @@
+#define _BSD_SOURCE
+#include <stdlib.h>
+
+typedef int (*cmpfun)(const void *, const void *);
+
+static int wrapper_cmp(const void *v1, const void *v2, void *cmp)
+{
+	return ((cmpfun)cmp)(v1, v2);
+}
+
+void qsort(void *base, size_t nel, size_t width, cmpfun cmp)
+{
+	__qsort_r(base, nel, width, wrapper_cmp, cmp);
+}