diff options
| author | Oskar Schirmer | 2009-06-11 14:51:15 +0100 |
|---|---|---|
| committer | Linus Torvalds | 2009-06-11 08:51:08 -0700 |
| commit | 8759ef32d992fc6c0bcbe40fca7aa302190918a5 (patch) | |
| tree | 316df64d3456597bf7f8ef7508654c82faf6a5fe /lib | |
| parent | 9f322ad064f9210e7d472dfe77e702274d5c9dba (diff) | |
lib: isolate rational fractions helper function
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>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Kconfig | 3 | ||||
| -rw-r--r-- | lib/Makefile | 1 | ||||
| -rw-r--r-- | lib/rational.c | 62 |
3 files changed, 66 insertions, 0 deletions
diff --git a/lib/Kconfig b/lib/Kconfig index 8ade0a7a91e0..9960be04cbbe 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -10,6 +10,9 @@ menu "Library routines" config BITREVERSE tristate +config RATIONAL + boolean + config GENERIC_FIND_FIRST_BIT bool diff --git a/lib/Makefile b/lib/Makefile index 33a40e40e3ee..1f6edefebffe 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -50,6 +50,7 @@ ifneq ($(CONFIG_HAVE_DEC_LOCK),y) endif obj-$(CONFIG_BITREVERSE) += bitrev.o +obj-$(CONFIG_RATIONAL) += rational.o obj-$(CONFIG_CRC_CCITT) += crc-ccitt.o obj-$(CONFIG_CRC16) += crc16.o obj-$(CONFIG_CRC_T10DIF)+= crc-t10dif.o diff --git a/lib/rational.c b/lib/rational.c new file mode 100644 index 000000000000..b3c099b5478e --- /dev/null +++ b/lib/rational.c @@ -0,0 +1,62 @@ +/* + * 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); |