1/*
 2 * rational fractions
 3 *
 4 * Copyright (C) 2009 emlix GmbH, Oskar Schirmer <oskar@scara.com>
 5 *
 6 * helper functions when coping with rational numbers
 7 */
 8
 9#include <linux/rational.h>
10#include <linux/compiler.h>
11#include <linux/export.h>
12
13/*
14 * calculate best rational approximation for a given fraction
15 * taking into account restricted register size, e.g. to find
16 * appropriate values for a pll with 5 bit denominator and
17 * 8 bit numerator register fields, trying to set up with a
18 * frequency ratio of 3.1415, one would say:
19 *
20 * rational_best_approximation(31415, 10000,
21 *		(1 << 8) - 1, (1 << 5) - 1, &n, &d);
22 *
23 * you may look at given_numerator as a fixed point number,
24 * with the fractional part size described in given_denominator.
25 *
26 * for theoretical background, see:
27 * http://en.wikipedia.org/wiki/Continued_fraction
28 */
29
30void rational_best_approximation(
31	unsigned long given_numerator, unsigned long given_denominator,
32	unsigned long max_numerator, unsigned long max_denominator,
33	unsigned long *best_numerator, unsigned long *best_denominator)
34{
35	unsigned long n, d, n0, d0, n1, d1;
36	n = given_numerator;
37	d = given_denominator;
38	n0 = d1 = 0;
39	n1 = d0 = 1;
40	for (;;) {
41		unsigned long t, a;
42		if ((n1 > max_numerator) || (d1 > max_denominator)) {
43			n1 = n0;
44			d1 = d0;
45			break;
46		}
47		if (d == 0)
48			break;
49		t = d;
50		a = n / d;
51		d = n % d;
52		n = t;
53		t = n0 + a * n1;
54		n0 = n1;
55		n1 = t;
56		t = d0 + a * d1;
57		d0 = d1;
58		d1 = t;
59	}
60	*best_numerator = n1;
61	*best_denominator = d1;
62}
63
64EXPORT_SYMBOL(rational_best_approximation);

 1/*
 2 * rational fractions
 3 *
 4 * Copyright (C) 2009 emlix GmbH, Oskar Schirmer <os@emlix.com>
 5 *
 6 * helper functions when coping with rational numbers
 7 */
 8
 9#include <linux/rational.h>
10#include <linux/module.h>
 
11
12/*
13 * calculate best rational approximation for a given fraction
14 * taking into account restricted register size, e.g. to find
15 * appropriate values for a pll with 5 bit denominator and
16 * 8 bit numerator register fields, trying to set up with a
17 * frequency ratio of 3.1415, one would say:
18 *
19 * rational_best_approximation(31415, 10000,
20 *		(1 << 8) - 1, (1 << 5) - 1, &n, &d);
21 *
22 * you may look at given_numerator as a fixed point number,
23 * with the fractional part size described in given_denominator.
24 *
25 * for theoretical background, see:
26 * http://en.wikipedia.org/wiki/Continued_fraction
27 */
28
29void rational_best_approximation(
30	unsigned long given_numerator, unsigned long given_denominator,
31	unsigned long max_numerator, unsigned long max_denominator,
32	unsigned long *best_numerator, unsigned long *best_denominator)
33{
34	unsigned long n, d, n0, d0, n1, d1;
35	n = given_numerator;
36	d = given_denominator;
37	n0 = d1 = 0;
38	n1 = d0 = 1;
39	for (;;) {
40		unsigned long t, a;
41		if ((n1 > max_numerator) || (d1 > max_denominator)) {
42			n1 = n0;
43			d1 = d0;
44			break;
45		}
46		if (d == 0)
47			break;
48		t = d;
49		a = n / d;
50		d = n % d;
51		n = t;
52		t = n0 + a * n1;
53		n0 = n1;
54		n1 = t;
55		t = d0 + a * d1;
56		d0 = d1;
57		d1 = t;
58	}
59	*best_numerator = n1;
60	*best_denominator = d1;
61}
62
63EXPORT_SYMBOL(rational_best_approximation);