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Date: Wed, 20 Dec 2017 16:41:46 +0100 From: Crt Mori <cmo@...exis.com> To: David Laight <David.Laight@...lab.com> Cc: Jonathan Cameron <jic23@...nel.org>, Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <keescook@...omium.org>, Rusty Russell <rusty@...tcorp.com.au>, Ian Abbott <abbotti@....co.uk>, Larry Finger <Larry.Finger@...inger.net>, Niklas Soderlund <niklas.soderlund+renesas@...natech.se>, Thomas Gleixner <tglx@...utronix.de>, Krzysztof Kozlowski <krzk@...nel.org>, Masahiro Yamada <yamada.masahiro@...ionext.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org>, Joe Perches <joe@...ches.com> Subject: Re: [PATCH v10 1/3] lib: Add strongly typed 64bit int_sqrt On 20 December 2017 at 15:39, David Laight <David.Laight@...lab.com> wrote: > From: Crt Mori >> Sent: 20 December 2017 14:20 >> >> 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. > > The algorithm used gives an exact (rounded down) square root, > not an approximation. > OK, noted. This is from new changed function indeed - will change in v11. > With minor changes it ought to be possible to remove most of the > 64bit arithmetic and shifts. > > If you care about performance then using 32 bit maths will be much faster. > I need precision not the performance. That is why I would like to leave int_sqrt as one for good performance while my will be used when you require a precision. > David >
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