From 9ccc92705ef428d6486fd9173e5029c594798919 Mon Sep 17 00:00:00 2001
From: Zandr Martin <zandrmartin+git@gmail.com>
Date: Thu, 2 Jun 2016 15:48:14 -0500
Subject: implement stable sort for lists

also change sort_workspaces() to use it
---
 common/list.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 58 insertions(+), 1 deletion(-)

(limited to 'common/list.c')

diff --git a/common/list.c b/common/list.c
index a7585a31..d57234e3 100644
--- a/common/list.c
+++ b/common/list.c
@@ -59,7 +59,7 @@ void list_cat(list_t *list, list_t *source) {
 	}
 }
 
-void list_qsort(list_t* list, int compare(const void *left, const void *right)) {
+void list_qsort(list_t *list, int compare(const void *left, const void *right)) {
 	qsort(list->items, list->length, sizeof(void *), compare);
 }
 
@@ -72,3 +72,60 @@ int list_seq_find(list_t *list, int compare(const void *item, const void *data),
 	}
 	return -1;
 }
+
+static void list_swap(list_t *list, int src, int dest) {
+	void *tmp = list->items[src];
+	list->items[src] = list->items[dest];
+	list->items[dest] = tmp;
+}
+
+static void list_rotate(list_t *list, int from, int to) {
+	void *tmp = list->items[to];
+
+	while (to > from) {
+		list->items[to] = list->items[to - 1];
+		to--;
+	}
+
+	list->items[from] = tmp;
+}
+
+static void list_inplace_merge(list_t *list, int left, int last, int mid, int compare(const void *a, const void *b)) {
+	int right = mid + 1;
+
+	if (compare(&list->items[mid], &list->items[right]) <= 0) {
+		return;
+	}
+
+	while (left <= mid && right <= last) {
+		if (compare(&list->items[left], &list->items[right]) <= 0) {
+			left++;
+		} else {
+			list_rotate(list, left, right);
+			left++;
+			mid++;
+			right++;
+		}
+	}
+}
+
+static void list_inplace_sort(list_t *list, int first, int last, int compare(const void *a, const void *b)) {
+	if (first >= last) {
+		return;
+	} else if ((last - first) == 1) {
+		if (compare(&list->items[first], &list->items[last]) > 0) {
+			list_swap(list, first, last);
+		}
+	} else {
+		int mid = (int)((last + first) / 2);
+		list_inplace_sort(list, first, mid, compare);
+		list_inplace_sort(list, mid + 1, last, compare);
+		list_inplace_merge(list, first, last, mid, compare);
+	}
+}
+
+void list_stable_sort(list_t *list, int compare(const void *a, const void *b)) {
+	if (list->length > 1) {
+		list_inplace_sort(list, 0, list->length - 1, compare);
+	}
+}
-- 
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