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. Although int_sqrt() is a rough
approximation, the same algorithm is used in int_sqrt64() as good
enough on 32bit platform.
Signed-off-by: Crt Mori <[email protected]>
---
include/linux/kernel.h | 6 ++++++
lib/int_sqrt.c | 32 ++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0ad4c3044cf9..f3bebd3a9213 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -459,6 +459,12 @@ extern int kernel_text_address(unsigned long addr);
extern int func_ptr_is_kernel_text(void *ptr);
unsigned long int_sqrt(unsigned long);
+#if BITS_PER_LONG != 64
+#define int_sqrt64 _int_sqrt64
+u32 _int_sqrt64(u64 x);
+#else
+#define int_sqrt64 int_sqrt
+#endif
extern void bust_spinlocks(int yes);
extern int oops_in_progress; /* If set, an oops, panic(), BUG() or die() is in progress */
diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
index 1ef4cc344977..84c77c934ec3 100644
--- a/lib/int_sqrt.c
+++ b/lib/int_sqrt.c
@@ -36,3 +36,35 @@ 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 <= 1)
+ return x;
+
+ m = 1ULL << (64 - 2);
+ 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
On Tue, 2017-12-19 at 16:59 +0100, Crt Mori wrote:
> 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. Although int_sqrt() is a rough
> approximation, the same algorithm is used in int_sqrt64() as good
> enough on 32bit platform.
>
> Signed-off-by: Crt Mori <[email protected]>
> ---
> include/linux/kernel.h | 6 ++++++
> lib/int_sqrt.c | 32 ++++++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 0ad4c3044cf9..f3bebd3a9213 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -459,6 +459,12 @@ extern int kernel_text_address(unsigned long addr);
> extern int func_ptr_is_kernel_text(void *ptr);
>
> unsigned long int_sqrt(unsigned long);
> +#if BITS_PER_LONG != 64
> +#define int_sqrt64 _int_sqrt64
> +u32 _int_sqrt64(u64 x);
> +#else
> +#define int_sqrt64 int_sqrt
> +#endif
As you've changed the return type for the 64-bit function to u32,
there is a unsigned long / u32 return mismatch on 64 bit platforms.
I suspect you need to define this as:
#define int_sqrt64(x) ((u32)int_sqrt(x))
> diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
[]
> @@ -36,3 +36,35 @@ 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 <= 1)
> + return x;
> +
> + m = 1ULL << (64 - 2);
Should probably use fls64 here.
> + while (m != 0) {
> + b = y + m;
> + y >>= 1;
> +
> + if (x >= b) {
> + x -= b;
> + y += m;
> + }
> + m >>= 2;
> + }
> +
> + return y;
> +}
> +EXPORT_SYMBOL(_int_sqrt64);
> +#endif
> +
On Tue, Dec 19, 2017 at 08:09:53AM -0800, Joe Perches wrote:
>
> I suspect you need to define this as:
>
> #define int_sqrt64(x) ((u32)int_sqrt(x))
What's wrong with using C ?
static inline u32 int_sqrt64(u64 x)
{
return int_sqrt(x);
}
On Tue, 2017-12-19 at 17:12 +0100, Peter Zijlstra wrote:
> On Tue, Dec 19, 2017 at 08:09:53AM -0800, Joe Perches wrote:
> >
> > I suspect you need to define this as:
> >
> > #define int_sqrt64(x) ((u32)int_sqrt(x))
>
> What's wrong with using C ?
Duh. Nothing at all.
> static inline u32 int_sqrt64(u64 x)
> {
> return int_sqrt(x);
> }
Thanks for suggestions and comments. Respinned v9 with them.
On 19 December 2017 at 17:14, Joe Perches <[email protected]> wrote:
> On Tue, 2017-12-19 at 17:12 +0100, Peter Zijlstra wrote:
>> On Tue, Dec 19, 2017 at 08:09:53AM -0800, Joe Perches wrote:
>> >
>> > I suspect you need to define this as:
>> >
>> > #define int_sqrt64(x) ((u32)int_sqrt(x))
>>
>> What's wrong with using C ?
>
> Duh. Nothing at all.
>
>> static inline u32 int_sqrt64(u64 x)
>> {
>> return int_sqrt(x);
>> }