libc: Implement an actual quicksort for qsort...

libc/stdlib/qsort.c

@@ -1,3 +1,4 @@
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stddef.h>
@@ -7,19 +8,46 @@
 extern char * _argv_0;
 extern int __libc_debug;
 
-void qsort(void * base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)) {
-	if (!nmemb) return;
-	if (!size) return;
-	for (size_t i = 0; i < nmemb-1; ++i) {
-		for (size_t j = 0; j < nmemb-1; ++j) {
-			void * left = (char *)base + size * j;
-			void * right = (char *)base + size * (j + 1);
-			if (compar(left,right) > 0) {
-				char tmp[size];
-				memcpy(tmp, right, size);
-				memcpy(right, left, size);
-				memcpy(left, tmp, size);
+struct SortableArray {
+	void * data;
+	size_t size;
+	int (*func)(const void *, const void *);
+};
+
+static ssize_t partition(struct SortableArray * array, ssize_t lo, ssize_t hi) {
+	char pivot[array->size];
+	memcpy(pivot, (char *)array->data + array->size * hi, array->size);
+	ssize_t i = lo - 1;
+	for (ssize_t j = lo; j <= hi; ++j) {
+		uint8_t * obj_j = (uint8_t *)array->data + array->size * j;
+		if (array->func(obj_j, pivot) <= 0) {
+			i++;
+			if (j != i) {
+				uint8_t * obj_i = (uint8_t *)array->data + array->size * i;
+				for (size_t x = 0; x < array->size; ++x) {
+					obj_j[x] ^= obj_i[x];
+					obj_i[x] ^= obj_j[x];
+					obj_j[x] ^= obj_i[x];
+				}
 			}
 		}
 	}
+	return i;
+}
+
+static void quicksort(struct SortableArray * array, ssize_t lo, ssize_t hi) {
+	if (lo >= 0 && hi >= 0) {
+		if (lo < hi) {
+			ssize_t pivot = partition(array, lo, hi);
+			quicksort(array, lo, pivot - 1);
+			quicksort(array, pivot + 1, hi);
+		}
+	}
+}
+
+void qsort(void * base, size_t nmemb, size_t size, int (*compar)(const void *, const void *)) {
+	if (nmemb < 2) return;
+	if (!size) return;
+	struct SortableArray array = {base,size,compar};
+	quicksort(&array, 0, nmemb - 1);
 }