2017-12-20 09:33:32

by Crt Mori

Subject: [PATCH v9 1/3] 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. 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 | 1 +
lib/int_sqrt.c | 37 +++++++++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 0ad4c3044cf9..5c6949e9e309 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr);
extern int func_ptr_is_kernel_text(void *ptr);

unsigned long int_sqrt(unsigned long);
+u32 int_sqrt64(u64 x);

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..30acab761dc1 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 +37,39 @@ 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 << (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);
+#else
+u32 int_sqrt64(u64 x)
+{
+ return int_sqrt(x);
+}
+EXPORT_SYMBOL(int_sqrt64);
+#endif
--
2.15.0

2017-12-20 09:56:38

by Joe Perches

Subject: Re: [PATCH v9 1/3] lib: Add strongly typed 64bit int_sqrt

On Wed, 2017-12-20 at 10:33 +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.
[]
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
[]
> @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr);
> extern int func_ptr_is_kernel_text(void *ptr);
>
> unsigned long int_sqrt(unsigned long);
> +u32 int_sqrt64(u64 x);

#ifdef BITS_PER_LONG == 64
static inline u32 int_sqrt64(u64 x)
{
re
turn (u32)int_sqrt(x);
}
#else
u32 int_sqrt64(u64 x);
#endif

[]

> +#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 << (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);
> +#else
> +u32 int_sqrt64(u64 x)
> +{
> + return int_sqrt(x);
> +}
> +EXPORT_SYMBOL(int_sqrt64);
> +#endif

This doesn't need to be EXPORT_SYMBOL for the
BITS_PER_LONG == 64 case

2017-12-20 14:20:24

by Crt Mori

Subject: Re: [PATCH v9 1/3] lib: Add strongly typed 64bit int_sqrt

On 20 December 2017 at 10:56, Joe Perches <[email protected]> wrote:
> On Wed, 2017-12-20 at 10:33 +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.
> []
>> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> []
>> @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr);
>> extern int func_ptr_is_kernel_text(void *ptr);
>>
>> unsigned long int_sqrt(unsigned long);
>> +u32 int_sqrt64(u64 x);
>
> #ifdef BITS_PER_LONG == 64
> static inline u32 int_sqrt64(u64 x)
> {
> re
> turn (u32)int_sqrt(x);
> }
> #else
> u32 int_sqrt64(u64 x);
> #endif
>
> []
>

OK, fixing it in v10.

>> +#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 << (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);
>> +#else
>> +u32 int_sqrt64(u64 x)
>> +{
>> + return int_sqrt(x);
>> +}
>> +EXPORT_SYMBOL(int_sqrt64);
>> +#endif
>
> This doesn't need to be EXPORT_SYMBOL for the
> BITS_PER_LONG == 64 case
>