CMSIS-DSP/Source/TransformFunctions/arm_mfcc_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_mfcc_q15.c
 * Description:  MFCC function for the q15 version
 *
 * $Date:        07 September 2021
 * $Revision:    V1.10.0
 *
 * Target Processor: Cortex-M and Cortex-A cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2021 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */



#include "dsp/transform_functions.h"
#include "dsp/statistics_functions.h"
#include "dsp/basic_math_functions.h"
#include "dsp/complex_math_functions.h"
#include "dsp/fast_math_functions.h"
#include "dsp/matrix_functions.h"

/* Constants for Q15 implementation */
#define LOG2TOLOG_Q15 0x02C5C860
#define MICRO_Q15 0x00000219
#define SHIFT_MELFILTER_SATURATION_Q15 10
/**
  @ingroup groupTransforms
 */


/**
  @defgroup MFCC MFCC

  MFCC Transform

  There are separate functions for floating-point, Q15, and Q15 data types.
 */



/**
  @addtogroup MFCC
  @{
 */

/**
  @brief         MFCC Q15
  @param[in]    S       points to the mfcc instance structure
  @param[in]     pSrc points to the input samples in Q15
  @param[out]     pDst  points to the output MFCC values in q8.7 format
  @param[inout]     pTmp  points to a temporary buffer of complex

  @return        none

  @par           Description
                   The number of input samples if the FFT length used
                   when initializing the instance data structure.

                   The temporary buffer has a 2*fft length.

                   The source buffer is modified by this function.

 */

arm_status arm_mfcc_q15(
  const arm_mfcc_instance_q15 * S,
  q15_t *pSrc,
  q15_t *pDst,
  q31_t *pTmp
  )
{
    q15_t m;
    uint32_t index;
    uint32_t fftShift=0;
    q31_t logExponent;
    q63_t result;
    arm_matrix_instance_q15 pDctMat;
    uint32_t i;
    uint32_t coefsPos;
    uint32_t filterLimit;
    q15_t *pTmp2=(q15_t*)pTmp;

    arm_status status = ARM_MATH_SUCCESS;
    
    // q15
    arm_absmax_q15(pSrc,S->fftLen,&m,&index);

    if (m !=0)
    {
       q15_t quotient;
       int16_t shift;

       status = arm_divide_q15(0x7FFF,m,&quotient,&shift);
       if (status != ARM_MATH_SUCCESS)
       {
          return(status);
       }
 
       arm_scale_q15(pSrc,quotient,shift,pSrc,S->fftLen);
    }


    // q15
    arm_mult_q15(pSrc,S->windowCoefs, pSrc, S->fftLen);


    /* Compute spectrum magnitude 
    */
    fftShift = 31 - __CLZ(S->fftLen);
#if defined(ARM_MFCC_CFFT_BASED)
    /* some HW accelerator for CMSIS-DSP used in some boards
       are only providing acceleration for CFFT.
       With ARM_MFCC_CFFT_BASED enabled, CFFT is used and the MFCC
       will be accelerated on those boards.
 
       The default is to use RFFT
    */
    /* Convert from real to complex */
    for(i=0; i < S->fftLen ; i++)
    {
      pTmp2[2*i] = pSrc[i];
      pTmp2[2*i+1] = 0;
    }
    arm_cfft_q15(&(S->cfft),pTmp2,0,1);
#else
    /* Default RFFT based implementation */
    arm_rfft_q15(&(S->rfft),pSrc,pTmp2);
#endif
    filterLimit = 1 + (S->fftLen >> 1);


    // q15 - fftShift
    arm_cmplx_mag_q15(pTmp2,pSrc,filterLimit);
    // q14 - fftShift

    /* Apply MEL filters */
    coefsPos = 0;
    for(i=0; i<S->nbMelFilters; i++)
    {
      arm_dot_prod_q15(pSrc+S->filterPos[i],
        &(S->filterCoefs[coefsPos]),
        S->filterLengths[i],
        &result);

      coefsPos += S->filterLengths[i];

      // q34.29 - fftShift
      result += MICRO_Q15;
      result >>= SHIFT_MELFILTER_SATURATION_Q15;
      // q34.29 - fftShift - satShift
      pTmp[i] = __SSAT(result,31) ;

    }


    // q34.29 - fftShift - satShift
    /* Compute the log */
    arm_vlog_q31(pTmp,pTmp,S->nbMelFilters);


    // q5.26
   
    logExponent = fftShift + 2 + SHIFT_MELFILTER_SATURATION_Q15;
    logExponent = logExponent * LOG2TOLOG_Q15;


    // q8.26
    arm_offset_q31(pTmp,logExponent,pTmp,S->nbMelFilters);
    arm_shift_q31(pTmp,-19,pTmp,S->nbMelFilters);
    for(i=0; i<S->nbMelFilters; i++)
    { 
      pSrc[i] = __SSAT((q15_t)pTmp[i],16);
    }

    // q8.7

    pDctMat.numRows=S->nbDctOutputs;
    pDctMat.numCols=S->nbMelFilters;
    pDctMat.pData=(q15_t*)S->dctCoefs;

    arm_mat_vec_mult_q15(&pDctMat, pSrc, pDst);

    return(status);
}

/**
  @} end of MFCC group
 */