altos: Rename 'core' to 'kernel'

[fw/altos] / src / kernel / ao_sqrt.c

diff --git a/src/kernel/ao_sqrt.c b/src/kernel/ao_sqrt.c
new file mode 100644 (file)
index 0000000..3a550ea
--- /dev/null
+++ b/src/kernel/ao_sqrt.c
@@ -0,0 +1,48 @@
+/*
+ * Copyright © 2011 Keith Packard <keithp@keithp.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
+ */
+
+#ifndef AO_FLIGHT_TEST
+#include "ao.h"
+#endif
+
+/* Adapted from int_sqrt.c in the linux kernel, which is licensed GPLv2 */
+/**
+ * int_sqrt - rough approximation to sqrt
+ * @x: integer of which to calculate the sqrt
+ *
+ * A very rough approximation to the sqrt() function.
+ */
+
+uint32_t
+ao_sqrt(uint32_t op)
+{
+       uint32_t        res = 0;
+       uint32_t        one = 1UL << (sizeof (one) * 8 - 2);
+
+       while (one > op)
+               one >>= 2;
+
+       while (one != 0) {
+               if (op >= res + one) {
+                       op = op - (res + one);
+                       res = res +  2 * one;
+               }
+               res /= 2;
+               one /= 4;
+       }
+       return res;
+}