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 MFCC
 */



/**
  @addtogroup MFCCQ15
  @{
 */

/**
  @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        error status
  
  @par           Description
                   The number of input samples is 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.

                   The function may saturate. If the FFT length is too
                   big and the number of MEL filters too small then the fixed
                   point computations may saturate.

 */
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) && (m != 0x7FFF))
    {
       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) ;

    }

    if ((m != 0) && (m != 0x7FFF))
    {
      arm_scale_q31(pTmp,m<<16,0,pTmp,S->nbMelFilters);
    }
   
    // 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 MFCCQ15 group
 */