/* ----------------------------------------------------------------------  
* 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_fast_q31.c  
*  
* Description:	Processing function for the  
*				Q31 Fast Biquad cascade DirectFormI(DF1) 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 0.0.9  2010/08/27   
*    Initial version  
*  
* -------------------------------------------------------------------- */ 
 
#include "arm_math.h" 
 
/**  
 * @ingroup groupFilters  
 */ 
 
/**  
 * @addtogroup BiquadCascadeDF1  
 * @{  
 */ 
 
/**  
 * @details  
 *  
 * @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  
 * This function is optimized for speed at the expense of fixed-point precision and overflow protection.  
 * The result of each 1.31 x 1.31 multiplication is truncated to 2.30 format.  
 * These intermediate results are added to a 2.30 accumulator.  
 * Finally, the accumulator is saturated and converted to a 1.31 result.  
 * The fast version has the same overflow behavior as the standard version and provides less precision since it discards the low 32 bits of each multiplication result.  
 * In order to avoid overflows completely the input signal must be scaled down by two bits and lie in the range [-0.25 +0.25). Use the intialization function  
 * arm_biquad_cascade_df1_init_q31() to initialize filter structure.  
 *  
 * \par  
 * Refer to the function <code>arm_biquad_cascade_df1_q31()</code> for a slower implementation of this function which uses 64-bit accumulation to provide higher precision.  Both the slow and the fast versions use the same instance structure.  
 * Use the function <code>arm_biquad_cascade_df1_init_q31()</code> to initialize the filter structure.  
 */ 
 
void arm_biquad_cascade_df1_fast_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  */ 
  q31_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               */ 
  int32_t shift = (int32_t) S->postShift + 1;    /*  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 variables acc ... acc3 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 = (q31_t) (((q63_t) b0 * Xn) >> 32); 
      /* acc +=  b1 * x[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32); 
      /* acc +=  b[2] * x[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32); 
      /* acc +=  a1 * y[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32); 
      /* acc +=  a2 * y[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32); 
 
      /* The result is converted to 1.31 , Yn2 variable is reused */ 
      Yn2 = 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 = (q31_t) (((q63_t) b0 * (Xn2)) >> 32); 
      /* acc +=  b1 * x[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn))) >> 32); 
      /* acc +=  b[2] * x[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn1))) >> 32); 
      /* acc +=  a1 * y[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn2))) >> 32); 
      /* acc +=  a2 * y[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn1))) >> 32); 
 
      /* The result is converted to 1.31, Yn1 variable is reused  */ 
      Yn1 = 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 = (q31_t) (((q63_t) b0 * (Xn1)) >> 32); 
      /* acc +=  b1 * x[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn2))) >> 32); 
      /* acc +=  b[2] * x[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn))) >> 32); 
      /* acc +=  a1 * y[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32); 
      /* acc +=  a2 * y[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32); 
 
      /* The result is converted to 1.31, Yn2 variable is reused  */ 
      Yn2 = 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 = (q31_t) (((q63_t) b0 * (Xn)) >> 32); 
      /* acc +=  b1 * x[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32); 
      /* acc +=  b[2] * x[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32); 
      /* acc +=  a1 * y[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn2))) >> 32); 
      /* acc +=  a2 * y[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn1))) >> 32); 
 
      /* The result is converted to 1.31, Yn1 variable is reused  */ 
      Yn1 = 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 = (q31_t) (((q63_t) b0 * (Xn)) >> 32); 
      /* acc +=  b1 * x[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b1 * (Xn1))) >> 32); 
      /* acc +=  b[2] * x[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) b2 * (Xn2))) >> 32); 
      /* acc +=  a1 * y[n-1] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a1 * (Yn1))) >> 32); 
      /* acc +=  a2 * y[n-2] */ 
      acc = (q31_t) ((((q63_t) acc << 32) + ((q63_t) a2 * (Yn2))) >> 32); 
      /* 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 = acc; 
 
      /* Store the output in the destination buffer. */ 
      *pOut++ = 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  
  */ 
