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rational.h (6283B)

---

/*
* rational numbers
* Copyright (c) 2003 Michael Niedermayer <michaelni@gmx.at>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

/**
* @file
* @ingroup lavu_math_rational
* Utilties for rational number calculation.
* @author Michael Niedermayer <michaelni@gmx.at>
*/

#ifndef AVUTIL_RATIONAL_H
#define AVUTIL_RATIONAL_H

#include <stdint.h>
#include <limits.h>
#include "attributes.h"

/**
* @defgroup lavu_math_rational AVRational
* @ingroup lavu_math
* Rational number calculation.
*
* While rational numbers can be expressed as floating-point numbers, the
* conversion process is a lossy one, so are floating-point operations. On the
* other hand, the nature of FFmpeg demands highly accurate calculation of
* timestamps. This set of rational number utilities serves as a generic
* interface for manipulating rational numbers as pairs of numerators and
* denominators.
*
* Many of the functions that operate on AVRational's have the suffix `_q`, in
* reference to the mathematical symbol "ℚ" (Q) which denotes the set of all
* rational numbers.
*
* @{
*/

/**
* Rational number (pair of numerator and denominator).
*/
typedef struct AVRational {
 int num;  ///< Numerator
 int den;  ///< Denominator
} AVRational;

/**
* Create an AVRational.
*
* Useful for compilers that do not support compound literals.
*
* @note The return value is not reduced.
* @see av_reduce()
*/
static inline AVRational av_make_q(int num, int den) {
 AVRational r = {num, den};
 return r;
}

/**
* Compare two rationals.
*
* @param a First rational
* @param b Second rational
*
* @return One of the following values:
*         - 0 if `a == b`
*         - 1 if `a > b`
*         - -1 if `a < b`
*         - `INT_MIN` if one of the values is of the form `0 / 0`
*/
static inline int av_cmp_q(AVRational a, AVRational b) {
 const int64_t tmp = a.num * (int64_t)b.den - b.num * (int64_t)a.den;

 if (tmp)
   return (int)((tmp ^ a.den ^ b.den) >> 63) | 1;
 else if (b.den && a.den)
   return 0;
 else if (a.num && b.num)
   return (a.num >> 31) - (b.num >> 31);
 else
   return INT_MIN;
}

/**
* Convert an AVRational to a `double`.
* @param a AVRational to convert
* @return `a` in floating-point form
* @see av_d2q()
*/
static inline double av_q2d(AVRational a) { return a.num / (double)a.den; }

/**
* Reduce a fraction.
*
* This is useful for framerate calculations.
*
* @param[out] dst_num Destination numerator
* @param[out] dst_den Destination denominator
* @param[in]      num Source numerator
* @param[in]      den Source denominator
* @param[in]      max Maximum allowed values for `dst_num` & `dst_den`
* @return 1 if the operation is exact, 0 otherwise
*/
int av_reduce(int* dst_num, int* dst_den, int64_t num, int64_t den,
             int64_t max);

/**
* Multiply two rationals.
* @param b First rational
* @param c Second rational
* @return b*c
*/
AVRational av_mul_q(AVRational b, AVRational c) av_const;

/**
* Divide one rational by another.
* @param b First rational
* @param c Second rational
* @return b/c
*/
AVRational av_div_q(AVRational b, AVRational c) av_const;

/**
* Add two rationals.
* @param b First rational
* @param c Second rational
* @return b+c
*/
AVRational av_add_q(AVRational b, AVRational c) av_const;

/**
* Subtract one rational from another.
* @param b First rational
* @param c Second rational
* @return b-c
*/
AVRational av_sub_q(AVRational b, AVRational c) av_const;

/**
* Invert a rational.
* @param q value
* @return 1 / q
*/
static av_always_inline AVRational av_inv_q(AVRational q) {
 AVRational r = {q.den, q.num};
 return r;
}

/**
* Convert a double precision floating point number to a rational.
*
* In case of infinity, the returned value is expressed as `{1, 0}` or
* `{-1, 0}` depending on the sign.
*
* In general rational numbers with |num| <= 1<<26 && |den| <= 1<<26
* can be recovered exactly from their double representation.
* (no exceptions were found within 1B random ones)
*
* @param d   `double` to convert
* @param max Maximum allowed numerator and denominator
* @return `d` in AVRational form
* @see av_q2d()
*/
AVRational av_d2q(double d, int max) av_const;

/**
* Find which of the two rationals is closer to another rational.
*
* @param q     Rational to be compared against
* @param q1    Rational to be tested
* @param q2    Rational to be tested
* @return One of the following values:
*         - 1 if `q1` is nearer to `q` than `q2`
*         - -1 if `q2` is nearer to `q` than `q1`
*         - 0 if they have the same distance
*/
int av_nearer_q(AVRational q, AVRational q1, AVRational q2);

/**
* Find the value in a list of rationals nearest a given reference rational.
*
* @param q      Reference rational
* @param q_list Array of rationals terminated by `{0, 0}`
* @return Index of the nearest value found in the array
*/
int av_find_nearest_q_idx(AVRational q, const AVRational* q_list);

/**
* Convert an AVRational to a IEEE 32-bit `float` expressed in fixed-point
* format.
*
* @param q Rational to be converted
* @return Equivalent floating-point value, expressed as an unsigned 32-bit
*         integer.
* @note The returned value is platform-indepedant.
*/
uint32_t av_q2intfloat(AVRational q);

/**
* Return the best rational so that a and b are multiple of it.
* If the resulting denominator is larger than max_den, return def.
*/
AVRational av_gcd_q(AVRational a, AVRational b, int max_den, AVRational def);

/**
* @}
*/

#endif /* AVUTIL_RATIONAL_H */