Diff: src/Cortex-M4-M3/StatisticsFunctions/arm_var_q15.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/StatisticsFunctions/arm_var_q15.c	Thu Mar 10 15:07:50 2011 +0000
@@ -0,0 +1,172 @@
+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:		arm_var_q15.c  
+*  
+* Description:	Variance of an array of Q15 type.  
+*  
+* 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 groupStats  
+ */ 
+ 
+/**  
+ * @addtogroup variance  
+ * @{  
+ */ 
+ 
+/**  
+ * @brief Variance of the elements of a Q15 vector.  
+ * @param[in]       *pSrc points to the input vector  
+ * @param[in]       blockSize length of the input vector  
+ * @param[out]      *pResult variance value returned here  
+ * @return none.  
+ *  
+ * @details  
+ * <b>Scaling and Overflow Behavior:</b>  
+ *  
+ * \par  
+ * The function is implemented using a 64-bit internal accumulator.  
+ * The input is represented in 1.15 format. 
+ * Intermediate multiplication yields a 2.30 format, and this  
+ * result is added without saturation to a 64-bit accumulator in 34.30 format.  
+ * With 33 guard bits in the accumulator, there is no risk of overflow, and the  
+ * full precision of the intermediate multiplication is preserved.  
+ * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower   
+ * 15 bits, and then saturated to yield a result in 1.15 format.  
+ *  
+ */ 
+ 
+ 
+void arm_var_q15( 
+  q15_t * pSrc, 
+  uint32_t blockSize, 
+  q31_t * pResult) 
+{ 
+  q63_t sum = 0;                                 /* Accumulator */ 
+  q31_t meanOfSquares, squareOfMean;             /* Mean of square and square of mean */ 
+  q15_t mean;                                    /* mean */ 
+  q31_t in;                                      /* Input variable */ 
+  q15_t in1;                                     /* Temporary variable */ 
+  uint32_t blkCnt;                               /* loop counter */ 
+  q15_t t;                                       /* Temporary variable */ 
+  q15_t *pIn;									 /* Temporary pointer */ 
+ 
+  pIn = pSrc; 
+ 
+  /*loop Unrolling */ 
+  blkCnt = blockSize >> 2u; 
+ 
+  /* 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) 
+  { 
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */ 
+    /* Compute Sum of squares of the input samples  
+     * and then store the result in a temporary variable, sum. */ 
+    in = *__SIMD32(pSrc)++; 
+    sum = __SMLALD(in, in, sum); 
+    in = *__SIMD32(pSrc)++; 
+    sum = __SMLALD(in, in, sum); 
+ 
+    /* 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) 
+  { 
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 
+    /* Compute Sum of squares of the input samples  
+     * and then store the result in a temporary variable, sum. */ 
+    in1 = *pSrc++; 
+    sum = __SMLALD(in1, in1, sum); 
+ 
+    /* Decrement the loop counter */ 
+    blkCnt--; 
+  } 
+ 
+  /* Compute Mean of squares of the input samples  
+   * and then store the result in a temporary variable, meanOfSquares. */ 
+  t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384); 
+  sum = __SSAT((sum >> 15u), 16u); 
+ 
+  meanOfSquares = (q31_t) ((sum * t) >> 14u); 
+ 
+  /* Reset the accumulator */ 
+  sum = 0; 
+ 
+  /*loop Unrolling */ 
+  blkCnt = blockSize >> 2u; 
+ 
+  /* Reset the input working pointer */ 
+  pSrc = pIn; 
+ 
+  /* 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) 
+  { 
+    /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ 
+    /* Compute sum of all input values and then store the result in a temporary variable, sum. */ 
+    sum += *pSrc++; 
+    sum += *pSrc++; 
+    sum += *pSrc++; 
+    sum += *pSrc++; 
+ 
+    /* 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) 
+  { 
+    /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ 
+    /* Compute sum of all input values and then store the result in a temporary variable, sum. */ 
+    sum += *pSrc++; 
+ 
+    /* Decrement the loop counter */ 
+    blkCnt--; 
+  } 
+ 
+  /* Compute mean of all input values */ 
+  t = (q15_t) ((1.0f / (float32_t) (blockSize * (blockSize - 1u))) * 32768); 
+  mean = __SSAT(sum, 16u); 
+ 
+  /* Compute square of mean */ 
+  squareOfMean = ((q31_t) mean * mean) >> 15; 
+  squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15); 
+ 
+  /* Compute variance and then store the result to the destination */ 
+  *pResult = (meanOfSquares - squareOfMean); 
+ 
+} 
+ 
+/**  
+ * @} end of variance group  
+ */