Diff: FilteringFunctions/arm_fir_decimate_fast_q31.c

Revision:

0:3d9c67d97d6f

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/FilteringFunctions/arm_fir_decimate_fast_q31.c	Mon Jul 28 15:03:15 2014 +0000
@@ -0,0 +1,351 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
+*    
+* $Date:        12. March 2014
+* $Revision: 	V1.4.3
+*    
+* Project: 	    CMSIS DSP Library    
+* Title:	    arm_fir_decimate_fast_q31.c    
+*    
+* Description:	Fast Q31 FIR Decimator.    
+*    
+* 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_decimate    
+ * @{    
+ */
+
+/**    
+ * @brief Processing function for the Q31 FIR decimator (fast variant) for Cortex-M3 and Cortex-M4.    
+ * @param[in] *S points to an instance of the Q31 FIR decimator 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 input 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 (where log2 is read as log to the base 2).    
+ *    
+ * \par    
+ * Refer to the function <code>arm_fir_decimate_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_decimate_init_q31()</code> to initialize the filter structure.    
+ */
+
+void arm_fir_decimate_fast_q31(
+  arm_fir_decimate_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, c0;                                  /* Temporary variables to hold state and coefficient values */
+  q31_t *px;                                     /* Temporary pointers for state buffer */
+  q31_t *pb;                                     /* Temporary pointers for coefficient buffer */
+  q31_t sum0;                                    /* Accumulator */
+  uint32_t numTaps = S->numTaps;                 /* Number of taps */
+  uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */
+  uint32_t blkCntN2;
+  q31_t x1;
+  q31_t acc0, acc1;
+  q31_t *px0, *px1;
+
+  /* S->pState buffer contains previous frame (numTaps - 1) samples */
+  /* pStateCurnt points to the location where the new input data should be written */
+  pStateCurnt = S->pState + (numTaps - 1u);
+
+  /* Total number of output samples to be computed */
+
+  blkCnt = outBlockSize / 2;
+  blkCntN2 = outBlockSize - (2 * blkCnt);
+
+  while(blkCnt > 0u)
+  {
+    /* Copy decimation factor number of new input samples into the state buffer */
+    i = 2 * S->M;
+
+    do
+    {
+      *pStateCurnt++ = *pSrc++;
+
+    } while(--i);
+
+    /* Set accumulator to zero */
+    acc0 = 0;
+    acc1 = 0;
+
+    /* Initialize state pointer */
+    px0 = pState;
+    px1 = pState + S->M;
+
+    /* Initialize coeff pointer */
+    pb = pCoeffs;
+
+    /* Loop unrolling.  Process 4 taps at a time. */
+    tapCnt = numTaps >> 2;
+
+    /* Loop over the number of taps.  Unroll by a factor of 4.       
+     ** Repeat until we've computed numTaps-4 coefficients. */
+    while(tapCnt > 0u)
+    {
+      /* Read the b[numTaps-1] coefficient */
+      c0 = *(pb);
+
+      /* Read x[n-numTaps-1] for sample 0 sample 1 */
+      x0 = *(px0);
+      x1 = *(px1);
+
+      /* Perform the multiply-accumulate */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* Read the b[numTaps-2] coefficient */
+      c0 = *(pb + 1u);
+
+      /* Read x[n-numTaps-2]  for sample 0 sample 1  */
+      x0 = *(px0 + 1u);
+      x1 = *(px1 + 1u);
+
+      /* Perform the multiply-accumulate */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* Read the b[numTaps-3] coefficient */
+      c0 = *(pb + 2u);
+
+      /* Read x[n-numTaps-3]  for sample 0 sample 1 */
+      x0 = *(px0 + 2u);
+      x1 = *(px1 + 2u);
+      pb += 4u;
+
+      /* Perform the multiply-accumulate */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* Read the b[numTaps-4] coefficient */
+      c0 = *(pb - 1u);
+
+      /* Read x[n-numTaps-4] for sample 0 sample 1 */
+      x0 = *(px0 + 3u);
+      x1 = *(px1 + 3u);
+
+
+      /* Perform the multiply-accumulate */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* update state pointers */
+      px0 += 4u;
+      px1 += 4u;
+
+      /* Decrement the loop counter */
+      tapCnt--;
+    }
+
+    /* If the filter length is not a multiple of 4, compute the remaining filter taps */
+    tapCnt = numTaps % 0x4u;
+
+    while(tapCnt > 0u)
+    {
+      /* Read coefficients */
+      c0 = *(pb++);
+
+      /* Fetch 1 state variable */
+      x0 = *(px0++);
+      x1 = *(px1++);
+
+      /* Perform the multiply-accumulate */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* Decrement the loop counter */
+      tapCnt--;
+    }
+
+    /* Advance the state pointer by the decimation factor       
+     * to process the next group of decimation factor number samples */
+    pState = pState + S->M * 2;
+
+    /* The result is in the accumulator, store in the destination buffer. */
+    *pDst++ = (q31_t) (acc0 << 1);
+    *pDst++ = (q31_t) (acc1 << 1);
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  while(blkCntN2 > 0u)
+  {
+    /* Copy decimation factor number of new input samples into the state buffer */
+    i = S->M;
+
+    do
+    {
+      *pStateCurnt++ = *pSrc++;
+
+    } while(--i);
+
+    /* Set accumulator to zero */
+    sum0 = 0;
+
+    /* Initialize state pointer */
+    px = pState;
+
+    /* Initialize coeff pointer */
+    pb = pCoeffs;
+
+    /* Loop unrolling.  Process 4 taps at a time. */
+    tapCnt = numTaps >> 2;
+
+    /* Loop over the number of taps.  Unroll by a factor of 4.       
+     ** Repeat until we've computed numTaps-4 coefficients. */
+    while(tapCnt > 0u)
+    {
+      /* Read the b[numTaps-1] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-1] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulate */
+      sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Read the b[numTaps-2] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-2] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulate */
+      sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Read the b[numTaps-3] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-3] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulate */
+      sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Read the b[numTaps-4] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-4] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulate */
+      sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Decrement the loop counter */
+      tapCnt--;
+    }
+
+    /* If the filter length is not a multiple of 4, compute the remaining filter taps */
+    tapCnt = numTaps % 0x4u;
+
+    while(tapCnt > 0u)
+    {
+      /* Read coefficients */
+      c0 = *(pb++);
+
+      /* Fetch 1 state variable */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulate */
+      sum0 = (q31_t) ((((q63_t) sum0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Decrement the loop counter */
+      tapCnt--;
+    }
+
+    /* Advance the state pointer by the decimation factor       
+     * to process the next group of decimation factor number samples */
+    pState = pState + S->M;
+
+    /* The result is in the accumulator, store in the destination buffer. */
+    *pDst++ = (q31_t) (sum0 << 1);
+
+    /* Decrement the loop counter */
+    blkCntN2--;
+  }
+
+  /* Processing is complete.       
+   ** Now copy the last numTaps - 1 samples to the satrt 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;
+
+  i = (numTaps - 1u) >> 2u;
+
+  /* copy data */
+  while(i > 0u)
+  {
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+
+    /* Decrement the loop counter */
+    i--;
+  }
+
+  i = (numTaps - 1u) % 0x04u;
+
+  /* copy data */
+  while(i > 0u)
+  {
+    *pStateCurnt++ = *pState++;
+
+    /* Decrement the loop counter */
+    i--;
+  }
+}
+
+/**    
+ * @} end of FIR_decimate group    
+ */