Diff: src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_q31.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_q31.c	Thu Mar 10 15:07:50 2011 +0000
@@ -0,0 +1,217 @@
+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:	    arm_fir_decimate_fast_q31.c  
+*  
+* Description:	Fast Q31 FIR Decimator.  
+*  
+* 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.  
+* -------------------------------------------------------------------- */ 
+ 
+#include "arm_math.h" 
+ 
+/**  
+ * @ingroup groupFilters  
+ */ 
+ 
+/**  
+ * @addtogroup FIR_decimate  
+ * @{  
+ */ 
+ 
+/**  
+ * @brief Processing function for the Q31 FIR decimator (fast variant).  
+ * @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 */ 
+  q63_t sum0;                                    /* Accumulator */ 
+  uint32_t numTaps = S->numTaps;                 /* Number of taps */ 
+  uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M;  /* Loop counters */ 
+ 
+ 
+  /* 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; 
+ 
+  while(blkCnt > 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) x0 * c0) + (sum0 << 32)) >> 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) x0 * c0) + (sum0 << 32)) >> 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) x0 * c0) + (sum0 << 32)) >> 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) x0 * c0) + (sum0 << 32)) >> 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) x0 * c0) + (sum0 << 32)) >> 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 */ 
+    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; 
+ 
+  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  
+ */