linux/lib/math/rational.c

// SPDX-License-Identifier: GPL-2.0
/*
 * rational fractions
 *
 * Copyright (C) 2009 emlix GmbH, Oskar Schirmer <[email protected]>
 * Copyright (C) 2019 Trent Piepho <[email protected]>
 *
 * helper functions when coping with rational numbers
 */

#include <linux/rational.h>
#include <linux/compiler.h>
#include <linux/export.h>
#include <linux/minmax.h>
#include <linux/limits.h>
#include <linux/module.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:
 * https://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)
{ … }

EXPORT_SYMBOL(…);

MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;