On Mon, 2017-12-18 at 16:05 +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);
> +u64 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
[]
> @@ -36,3 +36,29 @@ unsigned long int_sqrt(unsigned long x)
> return y;
> }
> EXPORT_SYMBOL(int_sqrt);
> +
> +/**
> + * int_sqrt64 - strongly typed int_sqrt function
> + * @x: 64bit integer of which to calculate the sqrt
> + */
> +u64 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);
int_sqrt is now optimized with __fls
Because u64 is unsigned long on 64 bit arches, this
could probably be optimized for 64 bit distributions
with something like:
#if BITS_PER_LONG != 64
#define int_sqrt64 _int_sqrt64
u64 _int_sqrt64(u64 x);
#else
#define int_sqrt64(x) int_sqrt
#endif
...
#if BITS_PER_LONG != 64
u64 _int_sqrt64(u64 x)
{ etc.. }
#endif
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