/*
 * 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);
ef='/cgit.cgi/linux/net-next.git/refs/?id=71810db27c1c853b335675bee335d893bc3d324b'>refs</a><a class='active' href='/cgit.cgi/linux/net-next.git/log/include/net/inet_sock.h'>log</a><a href='/cgit.cgi/linux/net-next.git/tree/include/net/inet_sock.h?id=71810db27c1c853b335675bee335d893bc3d324b'>tree</a><a href='/cgit.cgi/linux/net-next.git/commit/include/net/inet_sock.h?id=71810db27c1c853b335675bee335d893bc3d324b'>commit</a><a href='/cgit.cgi/linux/net-next.git/diff/include/net/inet_sock.h?id=71810db27c1c853b335675bee335d893bc3d324b'>diff</a></td><td class='form'><form class='right' method='get' action='/cgit.cgi/linux/net-next.git/log/include/net/inet_sock.h'>
<input type='hidden' name='id' value='71810db27c1c853b335675bee335d893bc3d324b'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/cgit.cgi/linux/net-next.git/log/?id=71810db27c1c853b335675bee335d893bc3d324b'>root</a>/<a href='/cgit.cgi/linux/net-next.git/log/include?id=71810db27c1c853b335675bee335d893bc3d324b'>include</a>/<a href='/cgit.cgi/linux/net-next.git/log/include/net?id=71810db27c1c853b335675bee335d893bc3d324b'>net</a>/<a href='/cgit.cgi/linux/net-next.git/log/include/net/inet_sock.h?id=71810db27c1c853b335675bee335d893bc3d324b'>inet_sock.h</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/cgit.cgi/linux/net-next.git/log/include/net/inet_sock.h?id=71810db27c1c853b335675bee335d893bc3d324b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th><th class='left'>Files</th><th class='left'>Lines</th></tr>