On Tue, 2018-01-09 at 16:18 +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. Using same algorithm as int_sqrt()
> with strong typing provides enough precision also on 32bit platforms,
> but it sacrifices some performance.
[]
> diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
[]
> @@ -36,3 +37,34 @@ 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;
> + u32 y = 0;
> +
> + if (x <= 1)
> + return x;
I think this should instead be:
if (x <= INT_MAX)
return int_sqrt((int)x);
to reduce the loop cost below when the
value is small enough.
> +
> + 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
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