Diff: cmsis_dsp/StatisticsFunctions/arm_std_q31.c

Revision:

1:fdd22bb7aa52

Child:

2:da51fb522205

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmsis_dsp/StatisticsFunctions/arm_std_q31.c	Wed Nov 28 12:30:09 2012 +0000
@@ -0,0 +1,184 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision:     V1.1.0  
+*    
+* Project:         CMSIS DSP Library    
+* Title:        arm_std_q31.c    
+*    
+* Description:    Standard deviation of an array of Q31 type.    
+*    
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*  
+* 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.    
+* -------------------------------------------------------------------- */
+
+#include "arm_math.h"
+
+/**    
+ * @ingroup groupStats    
+ */
+
+/**    
+ * @addtogroup STD    
+ * @{    
+ */
+
+
+/**    
+ * @brief Standard deviation of the elements of a Q31 vector.    
+ * @param[in]       *pSrc points to the input vector    
+ * @param[in]       blockSize length of the input vector    
+ * @param[out]      *pResult standard deviation value returned here    
+ * @return none.    
+ * @details    
+ * <b>Scaling and Overflow Behavior:</b>    
+ *    
+ *\par    
+ * The function is implemented using an internal 64-bit accumulator.    
+ * The input is represented in 1.31 format, and intermediate multiplication    
+ * yields a 2.62 format.    
+ * The accumulator maintains full precision of the intermediate multiplication results,     
+ * but provides only a single guard bit.    
+ * There is no saturation on intermediate additions.    
+ * If the accumulator overflows it wraps around and distorts the result.    
+ * In order to avoid overflows completely the input signal must be scaled down by     
+ * log2(blockSize) bits, as a total of blockSize additions are performed internally.     
+ * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.    
+ *    
+ */
+
+
+void arm_std_q31(
+  q31_t * pSrc,
+  uint32_t blockSize,
+  q31_t * pResult)
+{
+  q63_t sum = 0;                                 /* Accumulator */
+  q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
+  q31_t mean;                                    /* mean */
+  q31_t in;                                      /* input value */
+  q31_t t;                                       /* Temporary variable */
+  uint32_t blkCnt;                               /* loop counter */
+  q63_t sumOfSquares = 0;                        /* Accumulator */
+
+#ifndef ARM_MATH_CM0
+
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  /*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 = *pSrc++;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* 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. */
+    in = *pSrc++;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
+
+  /* Compute Mean of squares of the input samples    
+   * and then store the result in a temporary variable, meanOfSquares. */
+  sumOfSquares = (sumOfSquares >> 31);
+  meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
+
+#else
+
+  /* Run the below code for Cortex-M0 */
+
+  /* Loop over blockSize number of values */
+  blkCnt = blockSize;
+
+  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, sumOfSquares. */
+    in = *pSrc++;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* 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 += in;
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* Compute Mean of squares of the input samples     
+   * and then store the result in a temporary variable, meanOfSquares. */
+  t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
+  sumOfSquares = (sumOfSquares >> 31);
+  meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
+
+#endif /* #ifndef ARM_MATH_CM0 */
+
+  /* Compute mean of all input values */
+  t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
+  mean = (q31_t) (sum);
+
+  /* Compute square of mean */
+  squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
+  squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
+
+
+  /* Compute standard deviation and then store the result to the destination */
+  arm_sqrt_q31(meanOfSquares - squareOfMean, pResult);
+
+}
+
+/**    
+ * @} end of STD group    
+ */