[PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Crt Mori]

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 <cmo@melexis.com>
---
 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

Re: [PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Joe Perches]

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 <cmo@melexis.com>
> ---
>  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
> +

Re: [PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Peter Zijlstra]

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);
}

Re: [PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Joe Perches]

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);
> }

Re: [PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Joe Perches]

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);
> }

Re: [PATCH v7 1/3] lib: Add strongly typed 64bit int_sqrt

[Crt Mori]

Thanks for suggestions and comments. Respinned v9 with them.

On 19 December 2017 at 17:14, Joe Perches <joe@perches.com> 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);
>> }