Diff: src/Cortex-M4-M3/FilteringFunctions/arm_fir_fast_q15.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/FilteringFunctions/arm_fir_fast_q15.c	Thu Mar 10 15:07:50 2011 +0000
@@ -0,0 +1,267 @@
+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:        arm_fir_fast_q15.c  
+*  
+* Description:  Q15 Fast 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 0.0.9  2010/08/16   
+*    Initial version  
+*  
+* -------------------------------------------------------------------- */ 
+ 
+#include "arm_math.h" 
+ 
+/**  
+ * @ingroup groupFilters  
+ */ 
+ 
+/**  
+ * @addtogroup FIR  
+ * @{  
+ */ 
+ 
+/**  
+ * @param[in] *S points to an instance of the Q15 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.  
+ *  
+ * <b>Scaling and Overflow Behavior:</b>  
+ * \par  
+ * This fast version uses a 32-bit accumulator with 2.30 format.  
+ * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit.  
+ * Thus, if the accumulator result overflows it wraps around and distorts the result.  
+ * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits.  
+ * The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result.  
+ *  
+ * \par  
+ * Refer to the function <code>arm_fir_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion.  Both the slow and the fast versions use the same instance structure.  
+ * Use the function <code>arm_fir_init_q15()</code> to initialize the filter structure.  
+ */ 
+ 
+void arm_fir_fast_q15( 
+  const arm_fir_instance_q15 * S, 
+  q15_t * pSrc, 
+  q15_t * pDst, 
+  uint32_t blockSize) 
+{ 
+  q15_t *pState = S->pState;                     /* State pointer */ 
+  q15_t *pCoeffs = S->pCoeffs;                   /* Coefficient pointer */ 
+  q15_t *pStateCurnt;                            /* Points to the current sample of the state */ 
+  q15_t *px1;                                    /* Temporary q15 pointer for state buffer */ 
+  q31_t *pb;                                     /* Temporary pointer for coefficient buffer */ 
+  q31_t *px2;                                    /* Temporary q31 pointer for SIMD state buffer accesses */ 
+  q31_t x0, x1, x2, x3, c0;                      /* Temporary variables to hold SIMD state and coefficient values */ 
+  q31_t acc0, acc1, acc2, acc3;                  /* Accumulators */ 
+  uint32_t numTaps = S->numTaps;                 /* Number of taps in the filter */ 
+  uint32_t 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.  
+     ** Use 32-bit SIMD to move the 16-bit data.  Only requires two copies. */ 
+    *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; 
+    *__SIMD32(pStateCurnt)++ = *__SIMD32(pSrc)++; 
+ 
+    /* Set all accumulators to zero */ 
+    acc0 = 0; 
+    acc1 = 0; 
+    acc2 = 0; 
+    acc3 = 0; 
+ 
+    /* Initialize state pointer of type q15 */ 
+    px1 = pState; 
+ 
+    /* Initialize coeff pointer of type q31 */ 
+    pb = (q31_t *) (pCoeffs); 
+ 
+    /* Read the first two samples from the state buffer:  x[n-N], x[n-N-1] */ 
+    x0 = *(q31_t *) (px1++); 
+ 
+    /* Read the third and forth samples from the state buffer: x[n-N-1], x[n-N-2] */ 
+    x1 = *(q31_t *) (px1++); 
+ 
+    /* Loop over the number of taps.  Unroll by a factor of 4.  
+     ** Repeat until we've computed numTaps-4 coefficients. */ 
+    tapCnt = numTaps >> 2; 
+    do 
+    { 
+      /* Read the first two coefficients using SIMD:  b[N] and b[N-1] coefficients */ 
+      c0 = *(pb++); 
+ 
+      /* acc0 +=  b[N] * x[n-N] + b[N-1] * x[n-N-1] */ 
+      acc0 = __SMLAD(x0, c0, acc0); 
+ 
+      /* acc1 +=  b[N] * x[n-N-1] + b[N-1] * x[n-N-2] */ 
+      acc1 = __SMLAD(x1, c0, acc1); 
+ 
+      /* Read state x[n-N-2], x[n-N-3] */ 
+      x2 = *(q31_t *) (px1++); 
+ 
+      /* Read state x[n-N-3], x[n-N-4] */ 
+      x3 = *(q31_t *) (px1++); 
+ 
+      /* acc2 +=  b[N] * x[n-N-2] + b[N-1] * x[n-N-3] */ 
+      acc2 = __SMLAD(x2, c0, acc2); 
+ 
+      /* acc3 +=  b[N] * x[n-N-3] + b[N-1] * x[n-N-4] */ 
+      acc3 = __SMLAD(x3, c0, acc3); 
+ 
+      /* Read coefficients b[N-2], b[N-3] */ 
+      c0 = *(pb++); 
+ 
+      /* acc0 +=  b[N-2] * x[n-N-2] + b[N-3] * x[n-N-3] */ 
+      acc0 = __SMLAD(x2, c0, acc0); 
+ 
+      /* acc1 +=  b[N-2] * x[n-N-3] + b[N-3] * x[n-N-4] */ 
+      acc1 = __SMLAD(x3, c0, acc1); 
+ 
+      /* Read state x[n-N-4], x[n-N-5] */ 
+      x0 = *(q31_t *) (px1++); 
+ 
+      /* Read state x[n-N-5], x[n-N-6] */ 
+      x1 = *(q31_t *) (px1++); 
+ 
+      /* acc2 +=  b[N-2] * x[n-N-4] + b[N-3] * x[n-N-5] */ 
+      acc2 = __SMLAD(x0, c0, acc2); 
+ 
+      /* acc3 +=  b[N-2] * x[n-N-5] + b[N-3] * x[n-N-6] */ 
+      acc3 = __SMLAD(x1, c0, acc3); 
+      tapCnt--; 
+ 
+    } 
+    while(tapCnt > 0u); 
+ 
+    /* If the filter length is not a multiple of 4, compute the remaining filter taps.  
+     ** This is always 2 taps since the filter length is always even. */ 
+    if((numTaps & 0x3u) != 0u) 
+    { 
+      /* Read 2 coefficients */ 
+      c0 = *(pb++); 
+      /* Fetch 4 state variables */ 
+      x2 = *(q31_t *) (px1++); 
+      x3 = *(q31_t *) (px1++); 
+ 
+      /* Perform the multiply-accumulates */ 
+      acc0 = __SMLAD(x0, c0, acc0); 
+      acc1 = __SMLAD(x1, c0, acc1); 
+      acc2 = __SMLAD(x2, c0, acc2); 
+      acc3 = __SMLAD(x3, c0, acc3); 
+    } 
+ 
+    /* The results in the 4 accumulators are in 2.30 format.  Convert to 1.15 with saturation.  
+     ** Then store the 4 outputs in the destination buffer. */ 
+    *__SIMD32(pDst)++ = __PKHBT((acc0 >> 15), (acc1 >> 15), 16u); 
+    *__SIMD32(pDst)++ = __PKHBT((acc2 >> 15), (acc3 >> 15), 16u); 
+ 
+ 
+    /* Advance the state pointer by 4 to process the next group of 4 samples */ 
+    pState = pState + 4; 
+ 
+    /* Decrement the 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 % 0x4u; 
+  while(blkCnt > 0u) 
+  { 
+    /* Copy two samples into state buffer */ 
+    *pStateCurnt++ = *pSrc++; 
+ 
+    /* Set the accumulator to zero */ 
+    acc0 = 0; 
+ 
+    /* Use SIMD to hold states and coefficients */ 
+    px2 = (q31_t *) pState; 
+    pb = (q31_t *) (pCoeffs); 
+    tapCnt = numTaps >> 1; 
+ 
+    do 
+    { 
+      acc0 = __SMLAD(*px2++, *(pb++), acc0); 
+      tapCnt--; 
+    } 
+    while(tapCnt > 0u); 
+ 
+    /* The result is in 2.30 format.  Convert to 1.15 with saturation.  
+     ** Then store the output in the destination buffer. */ 
+    *pDst++ = (q15_t) ((acc0 >> 15)); 
+ 
+    /* Advance state pointer by 1 for the next sample */ 
+    pState = pState + 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; 
+  /* Calculation of count for copying integer writes */ 
+  tapCnt = (numTaps - 1u) >> 2; 
+ 
+  while(tapCnt > 0u) 
+  { 
+    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 
+    *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 
+ 
+    tapCnt--; 
+  } 
+ 
+  /* Calculation of count for remaining q15_t data */ 
+  tapCnt = (numTaps - 1u) % 0x4u; 
+ 
+  /* copy remaining data */ 
+  while(tapCnt > 0u) 
+  { 
+    *pStateCurnt++ = *pState++; 
+ 
+    /* Decrement the loop counter */ 
+    tapCnt--; 
+  } 
+} 
+ 
+/**  
+ * @} end of FIR group  
+ */