From: David Laight <David.Laight@ACULAB.COM>
To: "'Joe Perches'" <joe@perches.com>, "'Crt Mori'" <cmo@melexis.com>,
"Peter Zijlstra" <peterz@infradead.org>
Cc: Jonathan Cameron <jic23@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Kees Cook <keescook@chromium.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Ian Abbott <abbotti@mev.co.uk>,
"Larry Finger" <Larry.Finger@lwfinger.net>,
Niklas Soderlund <niklas.soderlund+renesas@ragnatech.se>,
Thomas Gleixner <tglx@linutronix.de>,
Krzysztof Kozlowski <krzk@kernel.org>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>
Subject: RE: [PATCH v10 1/3] lib: Add strongly typed 64bit int_sqrt
Date: Thu, 21 Dec 2017 10:02:32 +0000 [thread overview]
Message-ID: <24b40255d28242d7accc0b6a13b5ad1f@AcuMS.aculab.com> (raw)
In-Reply-To: <1513790375.1234.121.camel@perches.com>
From: Joe Perches
> Sent: 20 December 2017 17:20
...
> > I think this version works.
> > It doesn't have the optimisation for small values.
> >
> > unsigned int sqrt64(unsigned long long x)
> > {
> > unsigned int x_hi = x >> 32;
> >
> > unsigned int b = 0;
> > unsigned int y = 0;
> > unsigned int i;
> >
>
> Perhaps add:
>
> if (x <= UINT_MAX)
> return int_sqrt((unsigned long)x);
Actually something like:
i = 32;
if (!x_hi) {
x_hi = x;
i = 16;
}
if (!(x_hi & 0xffff0000)) {
x_hi <<= 16;
i -= 8;
}
Repeat for 0xff000000, 0xf0000000 and 0xc0000000 and adjust loop to count down.
David
>
> > for (i = 0; i < 32; i++) {
> > b <<= 2;
> > b |= x_hi >> 30;
> > x_hi <<= 2;
> > if (i == 15)
> > x_hi = x;
> > y <<= 1;
> > if (b > y)
> > b -= ++y;
> > }
> > return y;
> > }
> >
> > Put it through cc -O3 -m32 -c -o sqrt64.o sqrt64.c and then objdump sqrt64.o
> > and compare to that of your version.
> >
> > David
> >
next prev parent reply other threads:[~2017-12-21 10:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 14:20 [PATCH v10 1/3] lib: Add strongly typed 64bit int_sqrt Crt Mori
2017-12-20 14:39 ` David Laight
2017-12-20 15:41 ` Crt Mori
2017-12-20 16:00 ` Peter Zijlstra
2017-12-20 16:17 ` Crt Mori
2017-12-20 16:46 ` David Laight
2017-12-20 17:19 ` Joe Perches
2017-12-21 10:02 ` David Laight [this message]
2017-12-20 17:30 ` Crt Mori
2017-12-21 10:08 ` David Laight
2017-12-21 10:59 ` David Laight
2017-12-21 11:43 ` David Laight
2017-12-21 13:17 ` Crt Mori
2017-12-21 13:56 ` David Laight
2017-12-21 14:11 ` Peter Zijlstra
2017-12-21 14:48 ` David Laight
2017-12-22 13:44 ` Crt Mori
2018-01-09 15:18 ` Crt Mori
2018-01-12 9:41 ` David Laight
2018-01-15 8:17 ` Crt Mori
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