stdlib: add qsort (TEST)

CMakeLists.txt

@@ -149,6 +149,7 @@ set(SOURCES
   src/libc/stdlib/ldiv.c
   src/libc/stdlib/llabs.c
   src/libc/stdlib/lldiv.c
+  src/libc/stdlib/qsort.c
   src/libc/stdlib/reallocarray.c
   src/libc/stdlib/strto_fp.c
   src/libc/stdlib/strto_int.c

STATUS

@@ -115,7 +115,8 @@ DONE:       Function/symbol/macro is defined, builds, links, and is tested
      7.20.4.4  _Exit: DONE      (gint only)
 !    7.20.4.5  getenv: TODO
 !    7.20.4.6  system: TODO
-!    7.20.5  Searching and sorting utilities: TODO
+!    7.20.5.1  bsearch: TODO
+!    7.20.5.2  qsort: TEST
      7.20.6.1  abs, labs, llabs: DONE
      7.20.6.2  div, ldiv, lldiv: DONE
 !    7.20.7  Multibyte/wide character conversion functions: TODO

src/libc/stdlib/qsort.c

@@ -0,0 +1,45 @@
+#include <stdlib.h>
+#include <string.h>
+
+typedef int comp_func(void const *left, void const *right);
+
+static int partition(void *base, size_t size, comp_func *compare,
+	int low, int high)
+{
+	#define AT(n) (base + size * (n))
+
+	__attribute__((aligned(4))) char tmp[size], pivot[size];
+	memcpy(pivot, AT((low + high) >> 1), size);
+
+	int i = low - 1;
+	int j = high + 1;
+
+	while(1) {
+		do i++;
+		while(compare(AT(i), pivot) < 0);
+
+		do j--;
+		while(compare(AT(j), pivot) > 0);
+
+		if(i >= j) return j;
+
+		memcpy(tmp, AT(i), size);
+		memcpy(AT(i), AT(j), size);
+		memcpy(AT(j), tmp, size);
+	}
+}
+
+static void sort(void *base, size_t size, comp_func *compare,
+	int low, int high)
+{
+	if(low >= high) return;
+
+	int p = partition(base, size, compare, low, high);
+	sort(base, size, compare, low, p);
+	sort(base, size, compare, p+1, high);
+}
+
+void qsort(void *base, size_t n, size_t size, comp_func *compare)
+{
+	sort(base, size, compare, 0, n-1);
+}