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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>
This commit is contained in:
Crt Mori 2018-01-11 11:19:57 +01:00 committed by Jonathan Cameron
parent 213451076b
commit 47a3616348
2 changed files with 39 additions and 0 deletions
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9
include/linux/kernel.h
View File

@ -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;

30
lib/int_sqrt.c
View File

@ -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