Diff: cmsis_dsp/FilteringFunctions/arm_biquad_cascade_df1_f32.c

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1:fdd22bb7aa52

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--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmsis_dsp/FilteringFunctions/arm_biquad_cascade_df1_f32.c	Wed Nov 28 12:30:09 2012 +0000
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+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision:     V1.1.0  
+*    
+* Project:         CMSIS DSP Library    
+* Title:        arm_biquad_cascade_df1_f32.c    
+*    
+* Description:    Processing function for the    
+*               floating-point Biquad cascade DirectFormI(DF1) filter.    
+*    
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*  
+* Version 1.1.0 2012/02/15 
+*    Updated with more optimizations, bug fixes and minor API changes.  
+*   
+* Version 1.0.10 2011/7/15  
+*    Big Endian support added and Merged M0 and M3/M4 Source code.   
+*    
+* 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    
+ */
+
+/**    
+ * @defgroup BiquadCascadeDF1 Biquad Cascade IIR Filters Using Direct Form I Structure    
+ *    
+ * This set of functions implements arbitrary order recursive (IIR) filters.    
+ * The filters are implemented as a cascade of second order Biquad sections.    
+ * The functions support Q15, Q31 and floating-point data types.  
+ * Fast version of Q15 and Q31 also supported on CortexM4 and Cortex-M3.    
+ *    
+ * The functions operate on blocks of input and output data and each call to the function    
+ * processes <code>blockSize</code> samples through the filter.    
+ * <code>pSrc</code> points to the array of input data and    
+ * <code>pDst</code> points to the array of output data.    
+ * Both arrays contain <code>blockSize</code> values.    
+ *    
+ * \par Algorithm    
+ * Each Biquad stage implements a second order filter using the difference equation:    
+ * <pre>    
+ *     y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]    
+ * </pre>    
+ * A Direct Form I algorithm is used with 5 coefficients and 4 state variables per stage.    
+ * \image html Biquad.gif "Single Biquad filter stage"    
+ * Coefficients <code>b0, b1 and b2 </code> multiply the input signal <code>x[n]</code> and are referred to as the feedforward coefficients.    
+ * Coefficients <code>a1</code> and <code>a2</code> multiply the output signal <code>y[n]</code> and are referred to as the feedback coefficients.    
+ * Pay careful attention to the sign of the feedback coefficients.    
+ * Some design tools use the difference equation    
+ * <pre>    
+ *     y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a2 * y[n-2]    
+ * </pre>    
+ * In this case the feedback coefficients <code>a1</code> and <code>a2</code> must be negated when used with the CMSIS DSP Library.    
+ *    
+ * \par    
+ * Higher order filters are realized as a cascade of second order sections.    
+ * <code>numStages</code> refers to the number of second order stages used.    
+ * For example, an 8th order filter would be realized with <code>numStages=4</code> second order stages.    
+ * \image html BiquadCascade.gif "8th order filter using a cascade of Biquad stages"    
+ * A 9th order filter would be realized with <code>numStages=5</code> second order stages with the coefficients for one of the stages configured as a first order filter (<code>b2=0</code> and <code>a2=0</code>).    
+ *    
+ * \par    
+ * The <code>pState</code> points to state variables array.    
+ * Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.    
+ * The state variables are arranged in the <code>pState</code> array as:    
+ * <pre>    
+ *     {x[n-1], x[n-2], y[n-1], y[n-2]}    
+ * </pre>    
+ *    
+ * \par    
+ * The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.    
+ * The state array has a total length of <code>4*numStages</code> values.    
+ * The state variables are updated after each block of data is processed, the coefficients are untouched.    
+ *    
+ * \par Instance Structure    
+ * The coefficients and state variables for a filter are stored together in an instance data structure.    
+ * A separate instance structure must be defined for each filter.    
+ * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.    
+ * There are separate instance structure declarations for each of the 3 supported data types.    
+ *    
+ * \par Init Functions    
+ * There is also an associated initialization function for each data type.    
+ * The initialization function performs following operations:    
+ * - Sets the values of the internal structure fields.    
+ * - Zeros out the values in the state buffer.    
+ *    
+ * \par    
+ * Use of the initialization function is optional.    
+ * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.    
+ * To place an instance structure into a const data section, the instance structure must be manually initialized.    
+ * Set the values in the state buffer to zeros before static initialization.    
+ * The code below statically initializes each of the 3 different data type filter instance structures    
+ * <pre>    
+ *     arm_biquad_casd_df1_inst_f32 S1 = {numStages, pState, pCoeffs};    
+ *     arm_biquad_casd_df1_inst_q15 S2 = {numStages, pState, pCoeffs, postShift};    
+ *     arm_biquad_casd_df1_inst_q31 S3 = {numStages, pState, pCoeffs, postShift};    
+ * </pre>    
+ * where <code>numStages</code> is the number of Biquad stages in the filter; <code>pState</code> is the address of the state buffer;    
+ * <code>pCoeffs</code> is the address of the coefficient buffer; <code>postShift</code> shift to be applied.    
+ *    
+ * \par Fixed-Point Behavior    
+ * Care must be taken when using the Q15 and Q31 versions of the Biquad Cascade filter functions.    
+ * Following issues must be considered:    
+ * - Scaling of coefficients    
+ * - Filter gain    
+ * - Overflow and saturation    
+ *    
+ * \par    
+ * <b>Scaling of coefficients: </b>    
+ * Filter coefficients are represented as fractional values and    
+ * coefficients are restricted to lie in the range <code>[-1 +1)</code>.    
+ * The fixed-point functions have an additional scaling parameter <code>postShift</code>    
+ * which allow the filter coefficients to exceed the range <code>[+1 -1)</code>.    
+ * At the output of the filter's accumulator is a shift register which shifts the result by <code>postShift</code> bits.    
+ * \image html BiquadPostshift.gif "Fixed-point Biquad with shift by postShift bits after accumulator"    
+ * This essentially scales the filter coefficients by <code>2^postShift</code>.    
+ * For example, to realize the coefficients    
+ * <pre>    
+ *    {1.5, -0.8, 1.2, 1.6, -0.9}    
+ * </pre>    
+ * set the pCoeffs array to:    
+ * <pre>    
+ *    {0.75, -0.4, 0.6, 0.8, -0.45}    
+ * </pre>    
+ * and set <code>postShift=1</code>    
+ *    
+ * \par    
+ * <b>Filter gain: </b>    
+ * The frequency response of a Biquad filter is a function of its coefficients.    
+ * It is possible for the gain through the filter to exceed 1.0 meaning that the filter increases the amplitude of certain frequencies.    
+ * This means that an input signal with amplitude < 1.0 may result in an output > 1.0 and these are saturated or overflowed based on the implementation of the filter.    
+ * To avoid this behavior the filter needs to be scaled down such that its peak gain < 1.0 or the input signal must be scaled down so that the combination of input and filter are never overflowed.    
+ *    
+ * \par    
+ * <b>Overflow and saturation: </b>    
+ * For Q15 and Q31 versions, it is described separately as part of the function specific documentation below.    
+ */
+
+/**    
+ * @addtogroup BiquadCascadeDF1    
+ * @{    
+ */
+
+/**    
+ * @param[in]  *S         points to an instance of the floating-point 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.    
+ *    
+ */
+
+void arm_biquad_cascade_df1_f32(
+  const arm_biquad_casd_df1_inst_f32 * S,
+  float32_t * pSrc,
+  float32_t * pDst,
+  uint32_t blockSize)
+{
+  float32_t *pIn = pSrc;                         /*  source pointer            */
+  float32_t *pOut = pDst;                        /*  destination pointer       */
+  float32_t *pState = S->pState;                 /*  pState pointer            */
+  float32_t *pCoeffs = S->pCoeffs;               /*  coefficient pointer       */
+  float32_t acc;                                 /*  Simulates the accumulator */
+  float32_t b0, b1, b2, a1, a2;                  /*  Filter coefficients       */
+  float32_t Xn1, Xn2, Yn1, Yn2;                  /*  Filter pState variables   */
+  float32_t Xn;                                  /*  temporary input           */
+  uint32_t sample, stage = S->numStages;         /*  loop counters             */
+
+
+#ifndef ARM_MATH_CM0
+
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  do
+  {
+    /* Reading the coefficients */
+    b0 = *pCoeffs++;
+    b1 = *pCoeffs++;
+    b2 = *pCoeffs++;
+    a1 = *pCoeffs++;
+    a2 = *pCoeffs++;
+
+    /* Reading the pState 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]    
+     *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1]   + a2 * y[n-2]    
+     *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1]   + a2 * y[n-2]    
+     *    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 first input */
+      Xn = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+      Yn2 = (b0 * Xn) + (b1 * Xn1) + (b2 * Xn2) + (a1 * Yn1) + (a2 * Yn2);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = Yn2;
+
+      /* 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   */
+
+      /* 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] */
+      Yn1 = (b0 * Xn2) + (b1 * Xn) + (b2 * Xn1) + (a1 * Yn2) + (a2 * Yn1);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = Yn1;
+
+      /* 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   */
+
+      /* 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] */
+      Yn2 = (b0 * Xn1) + (b1 * Xn2) + (b2 * Xn) + (a1 * Yn1) + (a2 * Yn2);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = Yn2;
+
+      /* 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   */
+
+      /* 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] */
+      Yn1 = (b0 * Xn) + (b1 * Xn1) + (b2 * Xn2) + (a1 * Yn2) + (a2 * Yn1);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = Yn1;
+
+      /* 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;
+
+      /* 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 * Xn) + (b1 * Xn1) + (b2 * Xn2) + (a1 * Yn1) + (a2 * Yn2);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = acc;
+
+      /* 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;
+
+      /* decrement the loop counter */
+      sample--;
+
+    }
+
+    /*  Store the updated state variables back into the pState array */
+    *pState++ = Xn1;
+    *pState++ = Xn2;
+    *pState++ = Yn1;
+    *pState++ = Yn2;
+
+    /*  The first stage goes from the input buffer to the output buffer. */
+    /*  Subsequent numStages  occur in-place in the output buffer */
+    pIn = pDst;
+
+    /* Reset the output pointer */
+    pOut = pDst;
+
+    /* decrement the loop counter */
+    stage--;
+
+  } while(stage > 0u);
+
+#else
+
+  /* Run the below code for Cortex-M0 */
+
+  do
+  {
+    /* Reading the coefficients */
+    b0 = *pCoeffs++;
+    b1 = *pCoeffs++;
+    b2 = *pCoeffs++;
+    a1 = *pCoeffs++;
+    a2 = *pCoeffs++;
+
+    /* Reading the pState values */
+    Xn1 = pState[0];
+    Xn2 = pState[1];
+    Yn1 = pState[2];
+    Yn2 = pState[3];
+
+    /*      The variables acc holds the output value that is computed:        
+     *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1]   + a2 * y[n-2]        
+     */
+
+    sample = blockSize;
+
+    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 * Xn) + (b1 * Xn1) + (b2 * Xn2) + (a1 * Yn1) + (a2 * Yn2);
+
+      /* Store the result in the accumulator in the destination buffer. */
+      *pOut++ = acc;
+
+      /* 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;
+
+      /* decrement the loop counter */
+      sample--;
+    }
+
+    /*  Store the updated state variables back into the pState array */
+    *pState++ = Xn1;
+    *pState++ = Xn2;
+    *pState++ = Yn1;
+    *pState++ = Yn2;
+
+    /*  The first stage goes from the input buffer to the output buffer. */
+    /*  Subsequent numStages  occur in-place in the output buffer */
+    pIn = pDst;
+
+    /* Reset the output pointer */
+    pOut = pDst;
+
+    /* decrement the loop counter */
+    stage--;
+
+  } while(stage > 0u);
+
+#endif /*   #ifndef ARM_MATH_CM0         */
+
+}
+
+
+  /**    
+   * @} end of BiquadCascadeDF1 group    
+   */