make sort() generally available

Rather than having this general library function only on ia64, move it
into common code, to be used by x86 exception table sorting too.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/xen/common/sort.c b/xen/common/sort.c
new file mode 100644
index 0000000000..d96fc2af18
--- /dev/null
+++ b/xen/common/sort.c
@@ -0,0 +1,82 @@
+/*
+ * A fast, small, non-recursive O(nlog n) sort for the Linux kernel
+ *
+ * Jan 23 2005  Matt Mackall <mpm@selenic.com>
+ */
+
+#include <xen/types.h>
+
+static void u32_swap(void *a, void *b, int size)
+{
+    u32 t = *(u32 *)a;
+    *(u32 *)a = *(u32 *)b;
+    *(u32 *)b = t;
+}
+
+static void generic_swap(void *a, void *b, int size)
+{
+    char t;
+
+    do {
+        t = *(char *)a;
+        *(char *)a++ = *(char *)b;
+        *(char *)b++ = t;
+    } while ( --size > 0 );
+}
+
+/*
+ * sort - sort an array of elements
+ * @base: pointer to data to sort
+ * @num: number of elements
+ * @size: size of each element
+ * @cmp: pointer to comparison function
+ * @swap: pointer to swap function or NULL
+ *
+ * This function does a heapsort on the given array. You may provide a
+ * swap function optimized to your element type.
+ *
+ * Sorting time is O(n log n) both on average and worst-case. While
+ * qsort is about 20% faster on average, it suffers from exploitable
+ * O(n*n) worst-case behavior and extra memory requirements that make
+ * it less suitable for kernel use.
+ */
+
+void sort(void *base, size_t num, size_t size,
+          int (*cmp)(const void *, const void *),
+          void (*swap)(void *, void *, int size))
+{
+    /* pre-scale counters for performance */
+    int i = (num/2) * size, n = num * size, c, r;
+
+    if (!swap)
+        swap = (size == 4 ? u32_swap : generic_swap);
+
+    /* heapify */
+    for ( ; i >= 0; i -= size )
+    {
+        for ( r = i; r * 2 < n; r  = c )
+        {
+            c = r * 2;
+            if ( (c < n - size) && (cmp(base + c, base + c + size) < 0) )
+                c += size;
+            if ( cmp(base + r, base + c) >= 0 )
+                break;
+            swap(base + r, base + c, size);
+        }
+    }
+
+    /* sort */
+    for ( i = n - size; i >= 0; i -= size )
+    {
+        swap(base, base + i, size);
+        for ( r = 0; r * 2 < i; r = c )
+        {
+            c = r * 2;
+            if ( (c < i - size) && (cmp(base + c, base + c + size) < 0) )
+                c += size;
+            if ( cmp(base + r, base + c) >= 0 )
+                break;
+            swap(base + r, base + c, size);
+        }
+    }
+}