Diff: cmsis_dsp/FilteringFunctions/arm_fir_decimate_fast_q31.c

Revision:

1:fdd22bb7aa52

Child:

2:da51fb522205

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmsis_dsp/FilteringFunctions/arm_fir_decimate_fast_q31.c	Wed Nov 28 12:30:09 2012 +0000
@@ -0,0 +1,343 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision:     V1.1.0  
+*    
+* Project:         CMSIS DSP Library    
+* Title:        arm_fir_decimate_fast_q31.c    
+*    
+* Description:    Fast Q31 FIR Decimator.    
+*    
+* Target Processor: Cortex-M4/Cortex-M3
+*  
+* 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.    
+* -------------------------------------------------------------------- */
+
+#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    
+ */