Diff: src/Cortex-M4-M3/FilteringFunctions/arm_fir_q31.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/FilteringFunctions/arm_fir_q31.c	Thu Mar 10 15:07:50 2011 +0000
@@ -0,0 +1,300 @@
+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:	    arm_fir_q31.c  
+*  
+* Description:	Q31 FIR filter processing function.  
+*  
+* Target Processor: Cortex-M4/Cortex-M3
+*  
+* 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  
+ */ 
+ 
+/**  
+ * @addtogroup FIR  
+ * @{  
+ */ 
+ 
+/**  
+ * @param[in] *S points to an instance of the Q31 FIR filter 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.  
+ *  
+ * @details  
+ * <b>Scaling and Overflow Behavior:</b>  
+ * \par  
+ * The function is implemented using an internal 64-bit accumulator.  
+ * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.  
+ * Thus, if the accumulator result overflows it wraps around rather than clip.  
+ * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.  
+ * After all multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format.  
+ *  
+ * \par  
+ * Refer to the function <code>arm_fir_fast_q31()</code> for a faster but less precise implementation of this filter.  
+ */ 
+ 
+void arm_fir_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 */ 
+  q63_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 state array 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 += ((q63_t) x0 * c0); 
+ 
+      /* acc1 +=  b[numTaps] * x[n-numTaps-1] */ 
+      acc1 += ((q63_t) x1 * c0); 
+ 
+      /* acc2 +=  b[numTaps] * x[n-numTaps-2] */ 
+      acc2 += ((q63_t) x2 * c0); 
+ 
+      /* acc3 +=  b[numTaps] * x[n-numTaps-3] */ 
+      acc3 += ((q63_t) x3 * c0); 
+ 
+      /* Read the b[numTaps-1] coefficient */ 
+      c0 = *(pb++); 
+ 
+      /* Read x[n-numTaps-4] sample */ 
+      x0 = *(px++); 
+ 
+      /* Perform the multiply-accumulates */ 
+      acc0 += ((q63_t) x1 * c0); 
+      acc1 += ((q63_t) x2 * c0); 
+      acc2 += ((q63_t) x3 * c0); 
+      acc3 += ((q63_t) x0 * c0); 
+ 
+      /* Read the b[numTaps-2] coefficient */ 
+      c0 = *(pb++); 
+ 
+      /* Read x[n-numTaps-5] sample */ 
+      x1 = *(px++); 
+ 
+      /* Perform the multiply-accumulates */ 
+      acc0 += ((q63_t) x2 * c0); 
+      acc1 += ((q63_t) x3 * c0); 
+      acc2 += ((q63_t) x0 * c0); 
+      acc3 += ((q63_t) x1 * c0); 
+      /* Read the b[numTaps-3] coefficients */ 
+      c0 = *(pb++); 
+ 
+      /* Read x[n-numTaps-6] sample */ 
+      x2 = *(px++); 
+ 
+      /* Perform the multiply-accumulates */ 
+      acc0 += ((q63_t) x3 * c0); 
+      acc1 += ((q63_t) x0 * c0); 
+      acc2 += ((q63_t) x1 * c0); 
+      acc3 += ((q63_t) 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 */ 
+      acc0 += ((q63_t) x0 * c0); 
+      acc1 += ((q63_t) x1 * c0); 
+      acc2 += ((q63_t) x2 * c0); 
+      acc3 += ((q63_t) 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 >> 31u); 
+    *pDst++ = (q31_t) (acc1 >> 31u); 
+    *pDst++ = (q31_t) (acc2 >> 31u); 
+    *pDst++ = (q31_t) (acc3 >> 31u); 
+ 
+    /* 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 += (q63_t) * (px++) * (*(pb++)); 
+      i--; 
+    } while(i > 0u); 
+ 
+    /* The result is in 2.62 format.  Convert to 1.31  
+     ** Then store the output in the destination buffer. */ 
+    *pDst++ = (q31_t) (acc0 >> 31u); 
+ 
+    /* 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  
+ */