fixup! spell out interface of qsort_r

Implementations of qsort_r use different APIs. For example the arguments on Mac
OS are switched.

Author: jonasnick

src/hsort.h

@@ -13,9 +13,19 @@
 /* In-place, iterative heapsort with an interface matching glibc's qsort_r. This
  * is preferred over standard library implementations because they generally
  * make no guarantee about being fast for malicious inputs.
- * Remeber that heapsort is unstable.
+ * Remember that heapsort is unstable.
  *
- * See the qsort_r manpage for a description of the interface.
+ * In/Out: ptr: pointer to the array to sort. The contents of the array are
+ *              sorted in ascending order according to the comparison function.
+ * In:   count: number of elements in the array.
+ *        size: size in bytes of each element.
+ *         cmp: pointer to a comparison function that is called with two
+ *              arguments that point to the objects being compared. The cmp_data
+ *              argument of secp256k1_hsort is passed as third argument. The
+ *              function must return an integer less than, equal to, or greater
+ *              than zero if the first argument is considered to be respectively
+ *              less than, equal to, or greater than the second.
+ *    cmp_data: pointer passed as third argument to cmp.
  */
 static void secp256k1_hsort(void *ptr, size_t count, size_t size,
                             int (*cmp)(const void *, const void *, void *),