Eric Lee / linux-smarc-t335x-v3.2

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Commit 8759ef32d992fc6c0bcbe40fca7aa302190918a5

Authored by Oskar Schirmer
Committed by Linus Torvalds
1 parent 9f322ad064
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

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>

Showing 4 changed files with 85 additions and 0 deletions Side-by-side Diff

include/linux/rational.h
Diff comments   View file @ 8759ef3
  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 + * e.g. when calculating optimum numerator/denominator pairs for
  8 + * pll configuration taking into account restricted register size
  9 + */
  10 +
  11 +#ifndef _LINUX_RATIONAL_H
  12 +#define _LINUX_RATIONAL_H
  13 +
  14 +void rational_best_approximation(
  15 + unsigned long given_numerator, unsigned long given_denominator,
  16 + unsigned long max_numerator, unsigned long max_denominator,
  17 + unsigned long *best_numerator, unsigned long *best_denominator);
  18 +
  19 +#endif /* _LINUX_RATIONAL_H */
... ... @@ -10,6 +10,9 @@
10 10 config BITREVERSE
11 11 tristate
12 12  
  13 +config RATIONAL
  14 + boolean
  15 +
13 16 config GENERIC_FIND_FIRST_BIT
14 17 bool
15 18  
... ... @@ -50,6 +50,7 @@
50 50 endif
51 51  
52 52 obj-$(CONFIG_BITREVERSE) += bitrev.o
  53 +obj-$(CONFIG_RATIONAL) += rational.o
53 54 obj-$(CONFIG_CRC_CCITT) += crc-ccitt.o
54 55 obj-$(CONFIG_CRC16) += crc16.o
55 56 obj-$(CONFIG_CRC_T10DIF)+= crc-t10dif.o
  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 +
  11 +/*
  12 + * calculate best rational approximation for a given fraction
  13 + * taking into account restricted register size, e.g. to find
  14 + * appropriate values for a pll with 5 bit denominator and
  15 + * 8 bit numerator register fields, trying to set up with a
  16 + * frequency ratio of 3.1415, one would say:
  17 + *
  18 + * rational_best_approximation(31415, 10000,
  19 + * (1 << 8) - 1, (1 << 5) - 1, &n, &d);
  20 + *
  21 + * you may look at given_numerator as a fixed point number,
  22 + * with the fractional part size described in given_denominator.
  23 + *
  24 + * for theoretical background, see:
  25 + * http://en.wikipedia.org/wiki/Continued_fraction
  26 + */
  27 +
  28 +void rational_best_approximation(
  29 + unsigned long given_numerator, unsigned long given_denominator,
  30 + unsigned long max_numerator, unsigned long max_denominator,
  31 + unsigned long *best_numerator, unsigned long *best_denominator)
  32 +{
  33 + unsigned long n, d, n0, d0, n1, d1;
  34 + n = given_numerator;
  35 + d = given_denominator;
  36 + n0 = d1 = 0;
  37 + n1 = d0 = 1;
  38 + for (;;) {
  39 + unsigned long t, a;
  40 + if ((n1 > max_numerator) || (d1 > max_denominator)) {
  41 + n1 = n0;
  42 + d1 = d0;
  43 + break;
  44 + }
  45 + if (d == 0)
  46 + break;
  47 + t = d;
  48 + a = n / d;
  49 + d = n % d;
  50 + n = t;
  51 + t = n0 + a * n1;
  52 + n0 = n1;
  53 + n1 = t;
  54 + t = d0 + a * d1;
  55 + d0 = d1;
  56 + d1 = t;
  57 + }
  58 + *best_numerator = n1;
  59 + *best_denominator = d1;
  60 +}
  61 +
  62 +EXPORT_SYMBOL(rational_best_approximation);