Messages in this thread | | | Date | Mon, 18 Dec 2017 17:44:49 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 1/3] lib: Add strongly typed 64bit int_sqrt |
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On Mon, Dec 18, 2017 at 04:05:44PM +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.
You clearly haven't read a recent version of the file you're patching. Please take a moment to do so now.
> +/** > + * int_sqrt64 - strongly typed int_sqrt function > + * @x: 64bit integer of which to calculate the sqrt > + */ > +u64 int_sqrt64(u64 x)
Please explain how the result of sqrt(u64) can be larger than u32.
Also, I expect that this fact could be exploited to optimize this for 32bit archs if one were so inclined.
> +{ > + 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; > +}
so yeah, no, please try again after reading the current file.
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