/*
 * rational fractions
 *
 * Copyright (C) 2009 emlix GmbH, Oskar Schirmer <oskar@scara.com>
 *
 * helper functions when coping with rational numbers
 */

#include <linux/rational.h>
#include <linux/compiler.h>
#include <linux/export.h>

/*
 * calculate best rational approximation for a given fraction
 * taking into account restricted register size, e.g. to find
 * appropriate values for a pll with 5 bit denominator and
 * 8 bit numerator register fields, trying to set up with a
 * frequency ratio of 3.1415, one would say:
 *
 * rational_best_approximation(31415, 10000,
 *		(1 << 8) - 1, (1 << 5) - 1, &n, &d);
 *
 * you may look at given_numerator as a fixed point number,
 * with the fractional part size described in given_denominator.
 *
 * for theoretical background, see:
 * http://en.wikipedia.org/wiki/Continued_fraction
 */

void rational_best_approximation(
	unsigned long given_numerator, unsigned long given_denominator,
	unsigned long max_numerator, unsigned long max_denominator,
	unsigned long *best_numerator, unsigned long *best_denominator)
{
	unsigned long n, d, n0, d0, n1, d1;
	n = given_numerator;
	d = given_denominator;
	n0 = d1 = 0;
	n1 = d0 = 1;
	for (;;) {
		unsigned long t, a;
		if ((n1 > max_numerator) || (d1 > max_denominator)) {
			n1 = n0;
			d1 = d0;
			break;
		}
		if (d == 0)
			break;
		t = d;
		a = n / d;
		d = n % d;
		n = t;
		t = n0 + a * n1;
		n0 = n1;
		n1 = t;
		t = d0 + a * d1;
		d0 = d1;
		d1 = t;
	}
	*best_numerator = n1;
	*best_denominator = d1;
}

EXPORT_SYMBOL(rational_best_approximation);
><tr><td>
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<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/commit/?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>root</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>include</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include/target?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>target</a>/<a href='/cgit.cgi/linux/net-next.git/commit/include/target/iscsi?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>iscsi</a></div><div class='content'><div class='cgit-panel'><b>diff options</b><form method='get'><input type='hidden' name='id' value='edb6fa1a6452edf736c04d02e3f6de59043df69e'/><table><tr><td colspan='2'/></tr><tr><td class='label'>context:</td><td class='ctrl'><select name='context' onchange='this.form.submit();'><option value='1'>1</option><option value='2'>2</option><option value='3' selected='selected'>3</option><option value='4'>4</option><option value='5'>5</option><option value='6'>6</option><option value='7'>7</option><option value='8'>8</option><option value='9'>9</option><option value='10'>10</option><option value='15'>15</option><option value='20'>20</option><option value='25'>25</option><option value='30'>30</option><option value='35'>35</option><option value='40'>40</option></select></td></tr><tr><td class='label'>space:</td><td class='ctrl'><select name='ignorews' onchange='this.form.submit();'><option value='0' selected='selected'>include</option><option value='1'>ignore</option></select></td></tr><tr><td class='label'>mode:</td><td class='ctrl'><select name='dt' onchange='this.form.submit();'><option value='0' selected='selected'>unified</option><option value='1'>ssdiff</option><option value='2'>stat only</option></select></td></tr><tr><td/><td class='ctrl'><noscript><input type='submit' value='reload'/></noscript></td></tr></table></form></div><table summary='commit info' class='commit-info'>
<tr><th>author</th><td>Luuk Paulussen &lt;luuk.paulussen@alliedtelesis.co.nz&gt;</td><td class='right'>2016-12-08 11:43:34 +1300</td></tr>
<tr><th>committer</th><td>Ralf Baechle &lt;ralf@linux-mips.org&gt;</td><td class='right'>2016-12-11 11:19:04 +0100</td></tr>
<tr><th>commit</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/target/iscsi?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>edb6fa1a6452edf736c04d02e3f6de59043df69e</a> (<a href='/cgit.cgi/linux/net-next.git/patch/include/target/iscsi?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>patch</a>)</td></tr>
<tr><th>tree</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/tree/?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>f854dd896b1e5033a26f305ec9a50a87b1b13939</a> /<a href='/cgit.cgi/linux/net-next.git/tree/include/target/iscsi?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>include/target/iscsi</a></td></tr>
<tr><th>parent</th><td colspan='2' class='oid'><a href='/cgit.cgi/linux/net-next.git/commit/include/target/iscsi?id=3e5de27e940d00d8d504dfb96625fb654f641509'>3e5de27e940d00d8d504dfb96625fb654f641509</a> (<a href='/cgit.cgi/linux/net-next.git/diff/include/target/iscsi?id=edb6fa1a6452edf736c04d02e3f6de59043df69e&amp;id2=3e5de27e940d00d8d504dfb96625fb654f641509'>diff</a>)</td></tr></table>
<div class='commit-subject'>MIPS: Return -ENODEV from weak implementation of rtc_mips_set_time</div><div class='commit-msg'>The sync_cmos_clock function in kernel/time/ntp.c first tries to update
the internal clock of the cpu by calling the "update_persistent_clock64"
architecture specific function.  If this returns -ENODEV, it then tries
to update an external RTC using "rtc_set_ntp_time".

On the mips architecture, the weak implementation of the underlying
function would return 0 if it wasn't overridden.  This meant that the
sync_cmos_clock function would never try to update an external RTC
(if both CONFIG_GENERIC_CMOS_UPDATE and CONFIG_RTC_SYSTOHC are
configured)

Returning -ENODEV instead, means that an external RTC will be tried.

Signed-off-by: Luuk Paulussen &lt;luuk.paulussen@alliedtelesis.co.nz&gt;
Reviewed-by: Richard Laing &lt;richard.laing@alliedtelesis.co.nz&gt;
Reviewed-by: Scott Parlane &lt;scott.parlane@alliedtelesis.co.nz&gt;
Reviewed-by: Chris Packham &lt;chris.packham@alliedtelesis.co.nz&gt;
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14649/
Signed-off-by: Ralf Baechle &lt;ralf@linux-mips.org&gt;
</div><div class='diffstat-header'><a href='/cgit.cgi/linux/net-next.git/diff/?id=edb6fa1a6452edf736c04d02e3f6de59043df69e'>Diffstat</a> (limited to 'include/target/iscsi')</div><table summary='diffstat' class='diffstat'>