mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-24 05:04:00 +08:00
8759ef32d9
Provide a helper function to determine optimum numerator denominator value pairs taking into account restricted register size. Useful especially with PLL and other clock configurations. Signed-off-by: Oskar Schirmer <os@emlix.com> Signed-off-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
63 lines
1.5 KiB
C
63 lines
1.5 KiB
C
/*
|
|
* rational fractions
|
|
*
|
|
* Copyright (C) 2009 emlix GmbH, Oskar Schirmer <os@emlix.com>
|
|
*
|
|
* helper functions when coping with rational numbers
|
|
*/
|
|
|
|
#include <linux/rational.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);
|