38235bc145
Add MetaFraction, which consists of two integers, the numerator an the denominator. The utility function to convert a double to a MetaFraction comes from gstreamer. https://bugzilla.gnome.org/show_bug.cgi?id=784199
134 lines
3 KiB
C
134 lines
3 KiB
C
/*
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* Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
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* 2000 Wim Taymans <wtay@chello.be>
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* 2002 Thomas Vander Stichele <thomas@apestaart.org>
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the
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* Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
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* Boston, MA 02110-1301, USA.
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*
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* Fraction utility functions in this file comes from gstutils.c in gstreamer.
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*/
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#include "config.h"
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#include "core/meta-fraction.h"
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#include <glib.h>
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#include <math.h>
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#define MAX_TERMS 30
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#define MIN_DIVISOR 1.0e-10
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#define MAX_ERROR 1.0e-20
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static int
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greatest_common_divisor (int a,
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int b)
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{
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while (b != 0)
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{
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int temp = a;
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a = b;
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b = temp % b;
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}
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return ABS (a);
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}
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MetaFraction
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meta_fraction_from_double (double src)
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{
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double V, F; /* double being converted */
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int N, D; /* will contain the result */
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int A; /* current term in continued fraction */
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int64_t N1, D1; /* numerator, denominator of last approx */
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int64_t N2, D2; /* numerator, denominator of previous approx */
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int i;
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int gcd;
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gboolean negative = FALSE;
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/* initialize fraction being converted */
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F = src;
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if (F < 0.0)
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{
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F = -F;
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negative = TRUE;
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}
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V = F;
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/* initialize fractions with 1/0, 0/1 */
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N1 = 1;
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D1 = 0;
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N2 = 0;
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D2 = 1;
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N = 1;
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D = 1;
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for (i = 0; i < MAX_TERMS; i++)
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{
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/* get next term */
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A = (gint) F; /* no floor() needed, F is always >= 0 */
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/* get new divisor */
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F = F - A;
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/* calculate new fraction in temp */
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N2 = N1 * A + N2;
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D2 = D1 * A + D2;
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/* guard against overflow */
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if (N2 > G_MAXINT || D2 > G_MAXINT)
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break;
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N = N2;
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D = D2;
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/* save last two fractions */
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N2 = N1;
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D2 = D1;
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N1 = N;
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D1 = D;
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/* quit if dividing by zero or close enough to target */
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if (F < MIN_DIVISOR || fabs (V - ((gdouble) N) / D) < MAX_ERROR)
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break;
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/* Take reciprocal */
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F = 1 / F;
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}
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/* fix for overflow */
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if (D == 0)
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{
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N = G_MAXINT;
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D = 1;
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}
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/* fix for negative */
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if (negative)
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N = -N;
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/* simplify */
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gcd = greatest_common_divisor (N, D);
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if (gcd)
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{
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N /= gcd;
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D /= gcd;
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}
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return (MetaFraction) {
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.num = N,
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.denom = D
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};
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}
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