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 <c...@melexis.com>
---
include/linux/kernel.h | 9 +++++++++
lib/int_sqrt.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0ad4c3044cf9..e4a3dc64e650 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -460,6 +460,15 @@ 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 1ef4cc344977..77386bc611d0 100644
--- a/lib/int_sqrt.c
+++ b/lib/int_sqrt.c
@@ -7,6 +7,7 @@
#include <linux/kernel.h>
#include <linux/export.h>
+#include <linux/bitops.h>
/**
* int_sqrt - rough approximation to sqrt
@@ -36,3 +37,33 @@ 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
--
2.15.0
