util: split out sorting related calls to new sort-util.[ch]

src/basic/sort-util.c

@@ -0,0 +1,27 @@
+#include "sort-util.h"
+#include "alloc-util.h"
+
+/* hey glibc, APIs with callbacks without a user pointer are so useless */
+void *xbsearch_r(const void *key, const void *base, size_t nmemb, size_t size,
+                 __compar_d_fn_t compar, void *arg) {
+        size_t l, u, idx;
+        const void *p;
+        int comparison;
+
+        assert(!size_multiply_overflow(nmemb, size));
+
+        l = 0;
+        u = nmemb;
+        while (l < u) {
+                idx = (l + u) / 2;
+                p = (const uint8_t*) base + idx * size;
+                comparison = compar(key, p, arg);
+                if (comparison < 0)
+                        u = idx;
+                else if (comparison > 0)
+                        l = idx + 1;
+                else
+                        return (void *)p;
+        }
+        return NULL;
+}