lib/int_sqrt.c: optimize square root algorithm

[platform/adaptation/renesas_rcar/renesas_kernel.git] / lib / int_sqrt.c

diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
index fc2eeb7..1ef4cc3 100644 (file)
--- a/lib/int_sqrt.c
+++ b/lib/int_sqrt.c
@@ -1,3 +1,9 @@
+/*
+ * Copyright (C) 2013 Davidlohr Bueso <davidlohr.bueso@hp.com>
+ *
+ *  Based on the shift-and-subtract algorithm for computing integer
+ *  square root from Guy L. Steele.
+ */
 
 #include <linux/kernel.h>
 #include <linux/export.h>
@@ -10,23 +16,23 @@
  */
 unsigned long int_sqrt(unsigned long x)
 {
-       unsigned long op, res, one;
+       unsigned long b, m, y = 0;
 
-       op = x;
-       res = 0;
+       if (x <= 1)
+               return x;
 
-       one = 1UL << (BITS_PER_LONG - 2);
-       while (one > op)
-               one >>= 2;
+       m = 1UL << (BITS_PER_LONG - 2);
+       while (m != 0) {
+               b = y + m;
+               y >>= 1;
 
-       while (one != 0) {
-               if (op >= res + one) {
-                       op = op - (res + one);
-                       res = res +  2 * one;
+               if (x >= b) {
+                       x -= b;
+                       y += m;
                }
-               res /= 2;
-               one /= 4;
+               m >>= 2;
        }
-       return res;
+
+       return y;
 }
 EXPORT_SYMBOL(int_sqrt);