lib: Add strongly typed 64bit int_sqrt

There is no option to perform 64bit integer sqrt on 32bit platform.
Added stronger typed int_sqrt64 enables the 64bit calculations to
be performed on 32bit platforms. Using same algorithm as int_sqrt()
with strong typing provides enough precision also on 32bit platforms,
but it sacrifices some performance. In case values are smaller than
ULONG_MAX the standard int_sqrt is used for calculation to maximize the
performance due to more native calculations.

Signed-off-by: Crt Mori <cmo@melexis.com>
Acked-by: Joe Perches <joe@perches.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

2 files changed, 39 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index ce51455e2adf..2da80e079d56 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -479,6 +479,15 @@ extern int func_ptr_is_kernel_text(void *ptr);
 
 unsigned long int_sqrt(unsigned long);
 
+#if BITS_PER_LONG < 64
+u32 int_sqrt64(u64 x);
+#else
+static inline u32 int_sqrt64(u64 x)
+{
+        return (u32)int_sqrt(x);
+}
+#endif
+
 extern void bust_spinlocks(int yes);
 extern int oops_in_progress;            /* If set, an oops, panic(), BUG() or die() is in progress */
 extern int panic_timeout;
diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
index e2d329099bf7..14436f4ca6bd 100644
--- a/lib/int_sqrt.c
+++ b/lib/int_sqrt.c
@@ -38,3 +38,33 @@ unsigned long int_sqrt(unsigned long x)
         return y;
 }
 EXPORT_SYMBOL(int_sqrt);
+
+#if BITS_PER_LONG < 64
+/**
+ * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
+ * is expected.
+ * @x: 64bit integer of which to calculate the sqrt
+ */
+u32 int_sqrt64(u64 x)
+{
+        u64 b, m, y = 0;
+
+        if (x <= ULONG_MAX)
+                return int_sqrt((unsigned long) x);
+
+        m = 1ULL << (fls64(x) & ~1ULL);
+        while (m != 0) {
+                b = y + m;
+                y >>= 1;
+
+                if (x >= b) {
+                        x -= b;
+                        y += m;
+                }
+                m >>= 2;
+        }
+
+        return y;
+}
+EXPORT_SYMBOL(int_sqrt64);
+#endif