From 6d8802f47904dc0f4aca09e2ee7872cd9077e0ba Mon Sep 17 00:00:00 2001
From: Richard Thier <magosit@outlook.hu>
Date: Thu, 8 May 2025 22:47:52 +0200
Subject: [PATCH] schwab: fixed endless run, bug in hi not bigger then mid and
 lo because only indices are checked lol

---
 data.inc      |  6 +++---
 schwab_sort.h | 27 +++++++++++++++++++++------
 2 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/data.inc b/data.inc
index f93cf8b..895633f 100644
--- a/data.inc
+++ b/data.inc
@@ -1,4 +1,6 @@
 int data[] = {
+	8, 7, 2, 1, 0, 9, 6,1
+	/*8, 7, 2, 1, 0, 9, 6,
 	8, 7, 2, 1, 0, 9, 6,
 	8, 7, 2, 1, 0, 9, 6,
 	8, 7, 2, 1, 0, 9, 6,
@@ -7,7 +9,5 @@ int data[] = {
 	8, 7, 2, 1, 0, 9, 6,
 	8, 7, 2, 1, 0, 9, 6,
 	8, 7, 2, 1, 0, 9, 6,
-	8, 7, 2, 1, 0, 9, 6,
-	8, 7, 2, 1, 0, 9, 6,
-	8, 7, 2, 1, 0, 9, 6,
+	8, 7, 2, 1, 0, 9, 6,*/
 };
diff --git a/schwab_sort.h b/schwab_sort.h
index 0142286..81e069a 100644
--- a/schwab_sort.h
+++ b/schwab_sort.h
@@ -35,6 +35,9 @@ static inline uint32_t schwab_pick_pivot(sch_rand_state *state, uint32_t len) {
  * Expects: arr[plo] <= arr[pmid] <= arr[phi]
  * Results: arr[low..plo - 1] <= arr[plo..pmid - 1] <= arr[pmid..phi - 1] <= arr[phi.. high]
  *
+ * Also: Adding together lengths of all results arrays shrinks by 1 compared to start arr.
+ *       This means that we ensure recursions / loops always end in quicksort...
+ *
  * @param arr The array to partition
  * @param low Inclusive smallest index.
  * @param high Inclusive highest index.
@@ -50,15 +53,20 @@ static inline void schwab_partition(
 		int *pmid,
 		int *phi) {
 
-	/* Grab pivot values (keys of partitioning) */
-	uint32_t klo = arr[*plo];
-	uint32_t kmid = arr[*pmid];
-	uint32_t khi = arr[*phi];
+	/* [*] Swapping arr[phi]<->arr[high] ensures stop condition later */
+	uint32_t tmphi = arr[*phi];
+	arr[*phi] = arr[high];
+	arr[high] = tmphi;
 
 	/* Aren't inclusive end indices of 4 "blocks" - b0 is smallest vals */
 	int b0 = low, b1 = low, b2 = low, b3 = low;
 
-	while(b3 < high + 1) {
+	/* Keys only - no element copy is made here */
+	uint32_t klo = arr[*plo];
+	uint32_t kmid = arr[*pmid];
+	uint32_t khi = arr[*phi];
+
+	while(b3 < high) {
 		/* This I moved to be first for hot code path for constant / smallrange */
 		if(arr[b3] >= khi) {
 			++b3;
@@ -94,10 +102,17 @@ static inline void schwab_partition(
 		}
 	}
 
+	/* [*] Swap the chosen pivot to begin of last block */
+	/* This way we can return bigger index and by that */
+	/* this always removes an element per run at least */
+	tmphi = arr[b2];
+	arr[b2++] = arr[high];
+	arr[high] = tmphi;
+
 	/* Handle output vars as per doc comment */
 	*plo = b0;
 	*pmid = b1;
-	*phi = b2;
+	*phi = b2; /* Because of: [*] */
 }
 
 /** Always at most log(n) space needing 4-way quicksort-like alg */