File content as of revision 0:1014af42efd9:

/* ----------------------------------------------------------------------  
* Copyright (C) 2010 ARM Limited. All rights reserved.  
*  
* $Date:        29. November 2010  
* $Revision: 	V1.0.3  
*  
* Project: 	    CMSIS DSP Library  
* Title:	    arm_biquad_cascade_df1_q31.c  
*  
* Description:	Processing function for the  
*				Q31 Biquad cascade filter  
*  
* Target Processor: Cortex-M4/Cortex-M3
*  
* Version 1.0.3 2010/11/29 
*    Re-organized the CMSIS folders and updated documentation.  
*   
* Version 1.0.2 2010/11/11  
*    Documentation updated.   
*  
* Version 1.0.1 2010/10/05   
*    Production release and review comments incorporated.  
*  
* Version 1.0.0 2010/09/20   
*    Production release and review comments incorporated.  
*  
* Version 0.0.5  2010/04/26   
* 	 incorporated review comments and updated with latest CMSIS layer  
*  
* Version 0.0.3  2010/03/10   
*    Initial version  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @addtogroup BiquadCascadeDF1  
 * @{  
 */ 
 
/**  
 * @brief Processing function for the Q31 Biquad cascade filter.  
 * @param[in]  *S         points to an instance of the Q31 Biquad cascade structure.  
 * @param[in]  *pSrc      points to the block of input data.  
 * @param[out] *pDst      points to the block of output data.  
 * @param[in]  blockSize  number of samples to process per call.  
 * @return none.  
 *  
 * <b>Scaling and Overflow Behavior:</b>  
 * \par  
 * The function is implemented using an internal 64-bit accumulator.  
 * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.  
 * Thus, if the accumulator result overflows it wraps around rather than clip.  
 * In order to avoid overflows completely the input signal must be scaled down by 2 bits and lie in the range [-0.25 +0.25).  
 * After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by <code>postShift</code> bits and the result truncated to  
 * 1.31 format by discarding the low 32 bits.  
 *  
 * \par  
 * Refer to the function <code>arm_biquad_cascade_df1_fast_q31()</code> for a faster but less precise implementation of this filter.  
 */ 
 
void arm_biquad_cascade_df1_q31( 
  const arm_biquad_casd_df1_inst_q31 * S, 
  q31_t * pSrc, 
  q31_t * pDst, 
  uint32_t blockSize) 
{ 
  q31_t *pIn = pSrc;                             /*  input pointer initialization  */ 
  q31_t *pOut = pDst;                            /*  output pointer initialization */ 
  q31_t *pState = S->pState;                     /*  pState pointer initialization */ 
  q31_t *pCoeffs = S->pCoeffs;                   /*  coeff pointer initialization  */ 
  q63_t acc;                                     /*  accumulator                   */ 
  q31_t Xn1, Xn2, Yn1, Yn2;                      /*  Filter state variables        */ 
  q31_t b0, b1, b2, a1, a2;                      /*  Filter coefficients           */ 
  q31_t Xn;                                      /*  temporary input               */ 
  uint32_t shift = 32u - ((uint32_t) S->postShift + 1u);        /*  Shift to be applied to the output */ 
  uint32_t sample, stage = S->numStages;         /*  loop counters                     */ 
 
 
  do 
  { 
    /* Reading the coefficients */ 
    b0 = *pCoeffs++; 
    b1 = *pCoeffs++; 
    b2 = *pCoeffs++; 
    a1 = *pCoeffs++; 
    a2 = *pCoeffs++; 
 
    /* Reading the state values */ 
    Xn1 = pState[0]; 
    Xn2 = pState[1]; 
    Yn1 = pState[2]; 
    Yn2 = pState[3]; 
 
    /* Apply loop unrolling and compute 4 output values simultaneously. */ 
    /*      The variable acc hold output values that are being computed:  
     *  
     *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]  
     */ 
 
    sample = blockSize >> 2u; 
 
    /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
     ** a second loop below computes the remaining 1 to 3 samples. */ 
    while(sample > 0u) 
    { 
      /* Read the input */ 
      Xn = *pIn++; 
 
      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 
 
      /* acc =  b0 * x[n] */ 
      acc = (q63_t) b0 *Xn; 
      /* acc +=  b1 * x[n-1] */ 
      acc += (q63_t) b1 *Xn1; 
      /* acc +=  b[2] * x[n-2] */ 
      acc += (q63_t) b2 *Xn2; 
      /* acc +=  a1 * y[n-1] */ 
      acc += (q63_t) a1 *Yn1; 
      /* acc +=  a2 * y[n-2] */ 
      acc += (q63_t) a2 *Yn2; 
 
      /* The result is converted to 1.31 , Yn2 variable is reused */ 
      Yn2 = (q31_t) (acc >> shift); 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = Yn2; 
 
      /* Read the second input */ 
      Xn2 = *pIn++; 
 
      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 
 
      /* acc =  b0 * x[n] */ 
      acc = (q63_t) b0 *Xn2; 
      /* acc +=  b1 * x[n-1] */ 
      acc += (q63_t) b1 *Xn; 
      /* acc +=  b[2] * x[n-2] */ 
      acc += (q63_t) b2 *Xn1; 
      /* acc +=  a1 * y[n-1] */ 
      acc += (q63_t) a1 *Yn2; 
      /* acc +=  a2 * y[n-2] */ 
      acc += (q63_t) a2 *Yn1; 
 
 
      /* The result is converted to 1.31, Yn1 variable is reused  */ 
      Yn1 = (q31_t) (acc >> shift); 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = Yn1; 
 
      /* Read the third input  */ 
      Xn1 = *pIn++; 
 
      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 
 
      /* acc =  b0 * x[n] */ 
      acc = (q63_t) b0 *Xn1; 
      /* acc +=  b1 * x[n-1] */ 
      acc += (q63_t) b1 *Xn2; 
      /* acc +=  b[2] * x[n-2] */ 
      acc += (q63_t) b2 *Xn; 
      /* acc +=  a1 * y[n-1] */ 
      acc += (q63_t) a1 *Yn1; 
      /* acc +=  a2 * y[n-2] */ 
      acc += (q63_t) a2 *Yn2; 
 
      /* The result is converted to 1.31, Yn2 variable is reused  */ 
      Yn2 = (q31_t) (acc >> shift); 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = Yn2; 
 
      /* Read the forth input */ 
      Xn = *pIn++; 
 
      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 
 
      /* acc =  b0 * x[n] */ 
      acc = (q63_t) b0 *Xn; 
      /* acc +=  b1 * x[n-1] */ 
      acc += (q63_t) b1 *Xn1; 
      /* acc +=  b[2] * x[n-2] */ 
      acc += (q63_t) b2 *Xn2; 
      /* acc +=  a1 * y[n-1] */ 
      acc += (q63_t) a1 *Yn2; 
      /* acc +=  a2 * y[n-2] */ 
      acc += (q63_t) a2 *Yn1; 
 
      /* The result is converted to 1.31, Yn1 variable is reused  */ 
      Yn1 = (q31_t) (acc >> shift); 
 
      /* Every time after the output is computed state should be updated. */ 
      /* The states should be updated as:  */ 
      /* Xn2 = Xn1    */ 
      /* Xn1 = Xn     */ 
      /* Yn2 = Yn1    */ 
      /* Yn1 = acc    */ 
      Xn2 = Xn1; 
      Xn1 = Xn; 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = Yn1; 
 
      /* decrement the loop counter */ 
      sample--; 
    } 
 
    /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
     ** No loop unrolling is used. */ 
    sample = (blockSize & 0x3u); 
 
    while(sample > 0u) 
    { 
      /* Read the input */ 
      Xn = *pIn++; 
 
      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */ 
 
      /* acc =  b0 * x[n] */ 
      acc = (q63_t) b0 *Xn; 
      /* acc +=  b1 * x[n-1] */ 
      acc += (q63_t) b1 *Xn1; 
      /* acc +=  b[2] * x[n-2] */ 
      acc += (q63_t) b2 *Xn2; 
      /* acc +=  a1 * y[n-1] */ 
      acc += (q63_t) a1 *Yn1; 
      /* acc +=  a2 * y[n-2] */ 
      acc += (q63_t) a2 *Yn2; 
 
      /* The result is converted to 1.31  */ 
      acc = acc >> shift; 
 
      /* Every time after the output is computed state should be updated. */ 
      /* The states should be updated as:  */ 
      /* Xn2 = Xn1    */ 
      /* Xn1 = Xn     */ 
      /* Yn2 = Yn1    */ 
      /* Yn1 = acc    */ 
      Xn2 = Xn1; 
      Xn1 = Xn; 
      Yn2 = Yn1; 
      Yn1 = (q31_t) acc; 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = (q31_t) acc; 
 
      /* decrement the loop counter */ 
      sample--; 
    } 
 
    /*  The first stage goes from the input buffer to the output buffer. */ 
    /*  Subsequent stages occur in-place in the output buffer */ 
    pIn = pDst; 
 
    /* Reset to destination pointer */ 
    pOut = pDst; 
 
    /*  Store the updated state variables back into the pState array */ 
    *pState++ = Xn1; 
    *pState++ = Xn2; 
    *pState++ = Yn1; 
    *pState++ = Yn2; 
 
  } while(--stage); 
} 
 
/**  
  * @} end of BiquadCascadeDF1 group  
  */