Diff: cmsis_dsp/FilteringFunctions/arm_fir_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_fast_q31.c	Wed Nov 28 12:30:09 2012 +0000
@@ -0,0 +1,309 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision:     V1.1.0  
+*    
+* 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
+*  
+* 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 0.0.9  2010/08/27     
+*    Initial version    
+* -------------------------------------------------------------------- */
+
+#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.    
+ */
+
+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] */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* acc1 +=  b[numTaps] * x[n-numTaps-1] */
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* acc2 +=  b[numTaps] * x[n-numTaps-2] */
+      acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
+
+      /* acc3 +=  b[numTaps] * x[n-numTaps-3] */
+      acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
+
+      /* Read the b[numTaps-1] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-4] sample */
+      x0 = *(px++);
+
+      /* Perform the multiply-accumulates */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x1 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x2 * c0)) >> 32);
+      acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x3 * c0)) >> 32);
+      acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x0 * c0)) >> 32);
+
+      /* Read the b[numTaps-2] coefficient */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-5] sample */
+      x1 = *(px++);
+
+      /* Perform the multiply-accumulates */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x2 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x3 * c0)) >> 32);
+      acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x1 * c0)) >> 32);
+
+      /* Read the b[numTaps-3] coefficients */
+      c0 = *(pb++);
+
+      /* Read x[n-numTaps-6] sample */
+      x2 = *(px++);
+
+      /* Perform the multiply-accumulates */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x3 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x1 * c0)) >> 32);
+      acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x2 * c0)) >> 32);
+      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 */
+      acc0 = (q31_t) ((((q63_t) acc0 << 32) + ((q63_t) x0 * c0)) >> 32);
+      acc1 = (q31_t) ((((q63_t) acc1 << 32) + ((q63_t) x1 * c0)) >> 32);
+      acc2 = (q31_t) ((((q63_t) acc2 << 32) + ((q63_t) x2 * c0)) >> 32);
+      acc3 = (q31_t) ((((q63_t) acc3 << 32) + ((q63_t) x3 * c0)) >> 32);
+
+      /* 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
+    {
+      acc0 =
+        (q31_t) ((((q63_t) acc0 << 32) +
+                  ((q63_t) (*px++) * (*(pb++)))) >> 32);
+      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 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;
+
+  tapCnt = (numTaps - 1u) >> 2u;
+
+  /* copy data */
+  while(tapCnt > 0u)
+  {
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+    *pStateCurnt++ = *pState++;
+
+    /* Decrement the loop counter */
+    tapCnt--;
+  }
+
+  /* Calculate remaining number of copies */
+  tapCnt = (numTaps - 1u) % 0x4u;
+
+  /* Copy the remaining q31_t data */
+  while(tapCnt > 0u)
+  {
+    *pStateCurnt++ = *pState++;
+
+    /* Decrement the loop counter */
+    tapCnt--;
+  }
+
+
+}
+
+/**    
+ * @} end of FIR group    
+ */