Use the permute array in-line

Author: Raghuveer Devulapalli

lib/x86simdsort.h

@@ -9,22 +9,6 @@
 #define XSS_HIDE_SYMBOL __attribute__((visibility("hidden")))
 #define UNUSED(x) (void)(x)
 
-template <typename T>
-XSS_HIDE_SYMBOL void permute_array_in_place(T *A, std::vector<size_t> P)
-{
-    for (size_t i = 0; i < P.size(); i++) {
-        size_t curr = i;
-        size_t next = P[curr];
-        while (next != i) {
-            std::swap(A[curr], A[next]);
-            P[curr] = curr;
-            curr = next;
-            next = P[next];
-        }
-        P[curr] = curr;
-    }
-}
-
 namespace x86simdsort {
 
 // quicksort
@@ -55,14 +39,30 @@ argselect(T *arr, size_t k, size_t arrsize, bool hasnan = false);
 template <typename T, typename F>
 XSS_EXPORT_SYMBOL void object_qsort(T *arr, size_t arrsize, const F key_func)
 {
+    /* (1) Create a vector a keys */
     using return_type_of =
             typename decltype(std::function {key_func})::result_type;
-    std::vector<return_type_of> keys(arrsize);
+    std::vector<return_type_of> keys;
+    keys.reserve(arrsize);
     for (size_t ii = 0; ii < arrsize; ++ii) {
         keys[ii] = key_func(arr[ii]);
     }
+
+    /* (2) Call argsort based on the keys */
     std::vector<size_t> arg = x86simdsort::argsort(keys.data(), arrsize);
-    permute_array_in_place(arr, arg);
+
+    /* (3) Permute array in-place */
+    for (size_t i = 0; i < arrsize; i++) {
+        size_t curr = i;
+        size_t next = arg[curr];
+        while (next != i) {
+            std::swap(arr[curr], arr[next]);
+            arg[curr] = curr;
+            curr = next;
+            next = arg[next];
+        }
+        arg[curr] = curr;
+    }
 }
 
 } // namespace x86simdsort