Diff: FilteringFunctions/arm_fir_fast_q31.c

Revision:

0:3d9c67d97d6f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FilteringFunctions/arm_fir_fast_q31.c	Mon Jul 28 15:03:15 2014 +0000
@@ -0,0 +1,299 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
+*    
+* $Date:        12. March 2014  
+* $Revision: 	V1.4.3  
+*    
+* Project: 	    CMSIS DSP Library    
+* Title:	    arm_fir_fast_q31.c    
+*    
+* Description:	Processing function for the Q31 Fast FIR filter.    
+*    
+* Target Processor: Cortex-M4/Cortex-M3
+*  
+* Redistribution and use in source and binary forms, with or without 
+* modification, are permitted provided that the following conditions
+* are met:
+*   - Redistributions of source code must retain the above copyright
+*     notice, this list of conditions and the following disclaimer.
+*   - Redistributions in binary form must reproduce the above copyright
+*     notice, this list of conditions and the following disclaimer in
+*     the documentation and/or other materials provided with the 
+*     distribution.
+*   - Neither the name of ARM LIMITED nor the names of its contributors
+*     may be used to endorse or promote products derived from this
+*     software without specific prior written permission.
+*
+* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
+* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+* POSSIBILITY OF SUCH DAMAGE.    
+* -------------------------------------------------------------------- */
+
+#include "arm_math.h"
+
+/**    
+ * @ingroup groupFilters    
+ */
+
+/**    
+ * @addtogroup FIR    
+ * @{    
+ */
+
+/**    
+ * @param[in] *S points to an instance of the Q31 structure.    
+ * @param[in] *pSrc points to the block of input data.    
+ * @param[out] *pDst points to the block 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 log2(numTaps) bits.    
+ *    
+ * \par    
+ * Refer to the function <code>arm_fir_q31()</code> for a slower implementation of this function which uses a 64-bit accumulator to provide higher precision.  Both the slow and the fast versions use the same instance structure.    
+ * Use the function <code>arm_fir_init_q31()</code> to initialize the filter structure.    
+ */
+
+IAR_ONLY_LOW_OPTIMIZATION_ENTER
+void arm_fir_fast_q31(
+  const arm_fir_instance_q31 * S,
+  q31_t * pSrc,
+  q31_t * pDst,
+  uint32_t blockSize)
+{
+  q31_t *pState = S->pState;                     /* State pointer */
+  q31_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */
+  q31_t *pStateCurnt;                            /* Points to the current sample of the state */
+  q31_t x0, x1, x2, x3;                          /* Temporary variables to hold state */
+  q31_t c0;                                      /* Temporary variable to hold coefficient value */
+  q31_t *px;                                     /* Temporary pointer for state */
+  q31_t *pb;                                     /* Temporary pointer for coefficient buffer */
+  q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */
+  uint32_t numTaps = S->numTaps;                 /* Number of filter coefficients in the filter */
+  uint32_t i, tapCnt, blkCnt;                    /* Loop counters */
+
+  /* S->pState points to buffer which contains previous frame (numTaps - 1) samples */
+  /* pStateCurnt points to the location where the new input data should be written */
+  pStateCurnt = &(S->pState[(numTaps - 1u)]);
+
+  /* Apply loop unrolling and compute 4 output values simultaneously.    
+   * The variables acc0 ... acc3 hold output values that are being computed:    
+   *    
+   *    acc0 =  b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0]    
+   *    acc1 =  b[numTaps-1] * x[n-numTaps] +   b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1]    
+   *    acc2 =  b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] +   b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2]    
+   *    acc3 =  b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps]   +...+ b[0] * x[3]    
+   */
+  blkCnt = blockSize >> 2;
+
+  /* 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(blkCnt > 0u)
+  {
+    /* Copy four new input samples into the state buffer */
+    *pStateCurnt++ = *pSrc++;
+    *pStateCurnt++ = *pSrc++;
+    *pStateCurnt++ = *pSrc++;
+    *pStateCurnt++ = *pSrc++;
+
+    /* Set all accumulators to zero */
+    acc0 = 0;
+    acc1 = 0;
+    acc2 = 0;
+    acc3 = 0;
+
+    /* Initialize state pointer */
+    px = pState;
+
+    /* Initialize coefficient pointer */
+    pb = pCoeffs;
+
+    /* Read the first three samples from the state buffer:    
+     *  x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */
+    x0 = *(px++);
+    x1 = *(px++);
+    x2 = *(px++);
+
+    /* Loop unrolling.  Process 4 taps at a time. */
+    tapCnt = numTaps >> 2;
+    i = tapCnt;
+
+    while(i > 0u)
+    {
+      /* Read the b[numTaps] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-3] sample */
+      x3 = *(px++);
+
+      /* acc0 +=  b[numTaps] * x[n-numTaps] */
+      multAcc_32x32_keep32_R(acc0, x0, c0);
+
+      /* acc1 +=  b[numTaps] * x[n-numTaps-1] */
+      multAcc_32x32_keep32_R(acc1, x1, c0);
+
+      /* acc2 +=  b[numTaps] * x[n-numTaps-2] */
+      multAcc_32x32_keep32_R(acc2, x2, c0);
+
+      /* acc3 +=  b[numTaps] * x[n-numTaps-3] */
+      multAcc_32x32_keep32_R(acc3, x3, c0);
+
+      /* Read the b[numTaps-1] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-4] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulates */      
+      multAcc_32x32_keep32_R(acc0, x1, c0);
+      multAcc_32x32_keep32_R(acc1, x2, c0);
+      multAcc_32x32_keep32_R(acc2, x3, c0);
+      multAcc_32x32_keep32_R(acc3, x0, c0);
+
+      /* Read the b[numTaps-2] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-5] sample */
+      x1 = *(px++);
+
+      /* Perform the multiply-accumulates */      
+      multAcc_32x32_keep32_R(acc0, x2, c0);
+      multAcc_32x32_keep32_R(acc1, x3, c0);
+      multAcc_32x32_keep32_R(acc2, x0, c0);
+      multAcc_32x32_keep32_R(acc3, x1, c0);
+
+      /* Read the b[numTaps-3] coefficients */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-6] sample */
+      x2 = *(px++);
+
+      /* Perform the multiply-accumulates */      
+      multAcc_32x32_keep32_R(acc0, x3, c0);
+      multAcc_32x32_keep32_R(acc1, x0, c0);
+      multAcc_32x32_keep32_R(acc2, x1, c0);
+      multAcc_32x32_keep32_R(acc3, x2, c0);
+      i--;
+    }
+
+    /* If the filter length is not a multiple of 4, compute the remaining filter taps */
+
+    i = numTaps - (tapCnt * 4u);
+    while(i > 0u)
+    {
+      /* Read coefficients */
+      c0 = *(pb++);
+
+      /* Fetch 1 state variable */
+      x3 = *(px++);
+
+      /* Perform the multiply-accumulates */      
+      multAcc_32x32_keep32_R(acc0, x0, c0);
+      multAcc_32x32_keep32_R(acc1, x1, c0);
+      multAcc_32x32_keep32_R(acc2, x2, c0);
+      multAcc_32x32_keep32_R(acc3, x3, c0);
+
+      /* Reuse the present sample states for next sample */
+      x0 = x1;
+      x1 = x2;
+      x2 = x3;
+
+      /* Decrement the loop counter */
+      i--;
+    }
+
+    /* Advance the state pointer by 4 to process the next group of 4 samples */
+    pState = pState + 4;
+
+    /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.31    
+     ** Then store the 4 outputs in the destination buffer. */
+    *pDst++ = (q31_t) (acc0 << 1);
+    *pDst++ = (q31_t) (acc1 << 1);
+    *pDst++ = (q31_t) (acc2 << 1);
+    *pDst++ = (q31_t) (acc3 << 1);
+
+    /* Decrement the samples loop counter */
+    blkCnt--;
+  }
+
+
+  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
+   ** No loop unrolling is used. */
+  blkCnt = blockSize % 4u;
+
+  while(blkCnt > 0u)
+  {
+    /* Copy one sample at a time into state buffer */
+    *pStateCurnt++ = *pSrc++;
+
+    /* Set the accumulator to zero */
+    acc0 = 0;
+
+    /* Initialize state pointer */
+    px = pState;
+
+    /* Initialize Coefficient pointer */
+    pb = (pCoeffs);
+
+    i = numTaps;
+
+    /* Perform the multiply-accumulates */
+    do
+    {
+      multAcc_32x32_keep32_R(acc0, (*px++), (*(pb++)));
+      i--;
+    } while(i > 0u);
+
+    /* The result is in 2.30 format.  Convert to 1.31    
+     ** Then store the output in the destination buffer. */
+    *pDst++ = (q31_t) (acc0 << 1);
+
+    /* Advance state pointer by 1 for the next sample */
+    pState = pState + 1;
+
+    /* Decrement the samples loop counter */
+    blkCnt--;
+  }
+
+  /* Processing is complete.    
+   ** Now copy the last numTaps - 1 samples to the start of the state buffer.    
+   ** This prepares the state buffer for the next function call. */
+
+  /* Points to the start of the state buffer */
+  pStateCurnt = S->pState;
+
+  /* Calculate remaining number of copies */
+  tapCnt = (numTaps - 1u);
+
+  /* Copy the remaining q31_t data */
+  while(tapCnt > 0u)
+  {
+    *pStateCurnt++ = *pState++;
+
+    /* Decrement the loop counter */
+    tapCnt--;
+  }
+
+
+}
+IAR_ONLY_LOW_OPTIMIZATION_EXIT
+/**    
+ * @} end of FIR group    
+ */