From ec76ed2d14eda05f8d2c81e0b7aacdc079f2b275 Mon Sep 17 00:00:00 2001
From: Gregory Lirent <opensource@lirent.ru>
Date: Wed, 8 Jun 2022 21:19:03 +0300
Subject: [PATCH] Change list sort to stack-based

---
 src/list/sort.c | 61 +++++++++++++++++++++++++------------------------
 1 file changed, 31 insertions(+), 30 deletions(-)

diff --git a/src/list/sort.c b/src/list/sort.c
index 9162654..037881f 100644
--- a/src/list/sort.c
+++ b/src/list/sort.c
@@ -16,38 +16,39 @@ static inline void lnode_swap(lnode_t* s0, lnode_t* s1) {
     s1->type = t;
 }
 
-static inline lnode_t* pivot(lnode_t *l, lnode_t *r) {
-
-    lnode_t *c = l->prev;
-
-    for (lnode_t* i = l; i != r; i = i->next) {
-        if (lnode_compare(i, r) < 0) {
-            c = (is_null(c)) ? l : c->next;
-            lnode_swap(c, i);
-        }
-    }
-
-    c = (is_null(c)) ? l : c->next;
-    lnode_swap(c, r);
-
-    return c;
-}
-
-static void quick_sort(lnode_t* l, lnode_t* r) {
-    lnode_t* p;
-
-    if (!is_null(r) && l != r && l != r->next) {
-        p = pivot(l, r);
-
-        quick_sort(l, p->prev);
-        quick_sort(p->next, r);
-    }
-}
-
-/*#####################################################################################################################*/
 
 void list_sort(list_t* x) {
-    return quick_sort(x->first, x->last);
+    stack_t  z = { .prev = 0, .value = x->last};
+    lnode_t *l;
+    lnode_t *r;
+
+    stack_push(&z, x->first);
+
+    while (z.value) {
+
+        l = stack_pop(&z);
+        r = stack_pop(&z);
+
+        if (!is_null(r) && l != r && l != r->next) {
+
+            lnode_t *p = l->prev;
+
+            for (lnode_t* c = l; c != r; c = c->next) {
+                if (lnode_compare(c, r) < 0) {
+                    p = (is_null(p)) ? l : p->next;
+                    lnode_swap(p, c);
+                }
+            }
+
+            p = (is_null(p)) ? l : p->next;
+            lnode_swap(p, r);
+
+            stack_push(&z, r);
+            stack_push(&z, p->next);
+            stack_push(&z, p->prev);
+            stack_push(&z, l);
+        }
+    }
 }