[libc] Add isqrt() function to find integer square roots

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/isqrt.c

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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; either version 2 of the
+ * License, or any later version.
+ *
+ * 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., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/** @file
+ *
+ * Integer square root
+ *
+ */
+
+#include <ipxe/isqrt.h>
+
+/**
+ * Find integer square root
+ *
+ * @v value		Value
+ * @v isqrt		Integer square root of value
+ */
+unsigned long isqrt ( unsigned long value ) {
+	unsigned long result = 0;
+	unsigned long bit = ( 1UL << ( ( 8 * sizeof ( bit ) ) - 2 ) );
+
+	while ( bit > value )
+		bit >>= 2;
+	while ( bit ) {
+		if ( value >= ( result + bit ) ) {
+			value -= ( result + bit );
+			result = ( ( result >> 1 ) + bit );
+		} else {
+			result >>= 1;
+		}
+		bit >>= 2;
+	}
+	return result;
+}