/* * rational fractions * * Copyright (C) 2009 emlix GmbH, Oskar Schirmer <os@emlix.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);