/*
* Copyright (c) 2015-2020 Sergey Bakhurin
* Digital Signal Processing Library [http://dsplib.org]
*
* This file is part of DSPL.
*
* is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* DSPL 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
*/


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "dspl.h"



#ifdef DOXYGEN_ENGLISH
/*! ****************************************************************************
\ingroup FILTER_CONV_GROUP
\fn int conv(double* a, int na, double* b, int nb, double* c) 
\brief Real vectors linear convolution.

Function convolves two real vectors \f$ c = a * b\f$ length `na` and `nb`.
The output convolution is a vector `c` with length equal to  `na + nb - 1`. 

\param[in]  a
Pointer to the first vector `a`. \n
Vector size is `[na x 1]`. \n \n

\param[in]  na
Size of the first vector `a`. \n \n

\param[in]  b
Pointer to the second vector `b`. \n
Vector size is `[nb x 1]`. \n \n

\param[in]  nb
Size of the second vector `b`. \n \n

\param[out] c
Pointer to the convolution output vector  \f$ c = a * b\f$. \n
Vector size is `[na + nb - 1  x  1]`. \n
Memory must be allocated. \n \n

\return `RES_OK` if convolution is calculated successfully. \n
Else \ref ERROR_CODE_GROUP "code error".

\note If vectors `a` and `b` are coefficients of two polynomials,
then convolution of the vectors `a` and `b` returns polynomial product 
coefficients.

Example:
\code{.cpp}
    double ar[3] = {1.0, 2.0, 3.0};
    double br[4] = {3.0, -1.0, 2.0, 4.0};
    double cr[6];
    
    int n;
    
    conv(ar, 3, br, 4, cr);
    
    for(n = 0; n < 6; n++)
        printf("cr[%d] = %5.1f\n", n, cr[n]);

\endcode
\n

Output:
\verbatim
cr[0] =   3.0
cr[1] =   5.0
cr[2] =   9.0
cr[3] =   5.0
cr[4] =  14.0
cr[5] =  12.0
\endverbatim

\author Sergey Bakhurin www.dsplib.org
***************************************************************************** */
#endif
#ifdef DOXYGEN_RUSSIAN
/*! ****************************************************************************
\ingroup FILTER_CONV_GROUP
\fn int conv(double* a, int na, double* b, int nb, double* c) 
\brief Линейная свертка двух вещественных векторов

Функция рассчитывает линейную свертку двух векторов \f$ c = a * b\f$.

\param[in]  a
Указатель на первый вектор  \f$a\f$.  \n
Размер вектора `[na x 1]`.  \n \n 

\param[in]  na
Размер первого вектора. \n \n

\param[in]  b
Указатель на второй вектор \f$b\f$.  \n
Размер вектора `[nb x 1]`. \n  \n

\param[in]  nb
Размер второго вектора. \n \n

\param[out] c
Указатель на вектор свертки \f$ c = a * b\f$. \n
Размер вектора `[na + nb - 1  x  1]`. \n
Память должна быть выделена. \n \n

\return
`RES_OK` если свертка расчитана успешно. \n 
 В противном случае \ref ERROR_CODE_GROUP "код ошибки".

\note
Если вектора `a` и `b` представляют собой коэффициенты двух полиномов,
то результат линейной свертки представляет собой коэффициенты произведения
исходных полиномов.

Пример использования функции:

\code{.cpp}
    double ar[3] = {1.0, 2.0, 3.0};
    double br[4] = {3.0, -1.0, 2.0, 4.0};
    double cr[6];
    
    int n;
    
    conv(ar, 3, br, 4, cr);
    
    for(n = 0; n < 6; n++)
        printf("cr[%d] = %5.1f \n ", n, cr[n]);

\endcode
\n 

Результат работы:
\verbatim
cr[0] =   3.0
cr[1] =   5.0
cr[2] =   9.0
cr[3] =   5.0
cr[4] =  14.0
cr[5] =  12.0
\endverbatim

\author Бахурин Сергей. www.dsplib.org
***************************************************************************** */
#endif
int DSPL_API conv(double* a, int na, double* b, int nb, double* c)
{
    int k;
    int n;

    double *t;
    size_t bufsize;

    if(!a || !b || !c)
        return ERROR_PTR;
    if(na < 1 || nb < 1)
        return ERROR_SIZE;


    bufsize = (na + nb - 1) * sizeof(double);

    if((a != c) && (b != c))
        t = c;
    else
        t = (double*)malloc(bufsize);

    memset(t, 0, bufsize);

    for(k = 0; k < na; k++)
        for(n = 0; n < nb; n++)
            t[k+n] += a[k]*b[n];

    if(t!=c)
    {
        memcpy(c, t, bufsize);
        free(t);
    }
    return RES_OK;
}