Official ARM version: v5.6.0HEADmaster

1 files changed, 63 insertions, 85 deletions

diff --git a/DSP/Source/StatisticsFunctions/arm_std_q31.c b/DSP/Source/StatisticsFunctions/arm_std_q31.c
index f02cbdd..cfb6cb8 100644
--- a/DSP/Source/StatisticsFunctions/arm_std_q31.c
+++ b/DSP/Source/StatisticsFunctions/arm_std_q31.c
@@ -1,15 +1,15 @@
 /* ----------------------------------------------------------------------
  * Project:      CMSIS DSP Library
  * Title:        arm_std_q31.c
- * Description:  Standard deviation of an array of Q31 type.
+ * Description:  Standard deviation of the elements of a Q31 vector
  *
- * $Date:        27. January 2017
- * $Revision:    V.1.5.1
+ * $Date:        18. March 2019
+ * $Revision:    V1.6.0
  *
  * Target Processor: Cortex-M cores
  * -------------------------------------------------------------------- */
 /*
- * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
+ * Copyright (C) 2010-2019 ARM Limited or its affiliates. All rights reserved.
  *
  * SPDX-License-Identifier: Apache-2.0
  *
@@ -29,141 +29,119 @@
 #include "arm_math.h"
 
 /**
- * @ingroup groupStats
+  @ingroup groupStats
  */
 
 /**
- * @addtogroup STD
- * @{
+  @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, which is then downshifted by 8 bits
- * which yields 1.23, and intermediate multiplication yields a 2.46 format.
- * The accumulator maintains full precision of the intermediate multiplication results,
- * but provides only a 16 guard bits.
- * 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)-8 bits, as a total of blockSize additions are performed internally.
- * After division, internal variables should be Q18.46
- * Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value.
- *
+  @brief         Standard deviation of the elements of a Q31 vector.
+  @param[in]     pSrc       points to the input vector.
+  @param[in]     blockSize  number of samples in input vector.
+  @param[out]    pResult    standard deviation value returned here.
+  @return        none
+
+  @par           Scaling and Overflow Behavior
+                   The function is implemented using an internal 64-bit accumulator.
+                   The input is represented in 1.31 format, which is then downshifted by 8 bits
+                   which yields 1.23, and intermediate multiplication yields a 2.46 format.
+                   The accumulator maintains full precision of the intermediate multiplication results,
+                   but provides only a 16 guard bits.
+                   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)-8 bits, as a total of blockSize additions are performed internally.
+                   After division, internal variables should be Q18.46
+                   Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value.
  */
 
 void arm_std_q31(
-  q31_t * pSrc,
-  uint32_t blockSize,
-  q31_t * pResult)
+  const q31_t * pSrc,
+        uint32_t blockSize,
+        q31_t * pResult)
 {
-  q63_t sum = 0;                                 /* Accumulator */
-  q63_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
-  q31_t in;                                      /* input value */
-  uint32_t blkCnt;                               /* loop counter */
-  q63_t sumOfSquares = 0;                        /* Accumulator */
+        uint32_t blkCnt;                               /* Loop counter */
+        q63_t sum = 0;                                 /* Accumulator */
+        q63_t meanOfSquares, squareOfMean;             /* Square of mean and mean of square */
+        q63_t sumOfSquares = 0;                        /* Sum of squares */
+        q31_t in;                                      /* Temporary variable to store input value */
 
-  if (blockSize == 1U)
+  if (blockSize <= 1U)
   {
     *pResult = 0;
     return;
   }
 
-#if defined (ARM_MATH_DSP)
-  /* Run the below code for Cortex-M4 and Cortex-M3 */
+#if defined (ARM_MATH_LOOPUNROLL)
 
-  /*loop Unrolling */
+  /* Loop unrolling: Compute 4 outputs at a time */
   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. */
+    /* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
+    /* C = A[0] + A[1] + ... + A[blockSize-1] */
+
     in = *pSrc++ >> 8U;
-    sum += in;
+    /* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
     sumOfSquares += ((q63_t) (in) * (in));
-    in = *pSrc++ >> 8U;
+    /* Compute sum and store result in a temporary variable, sum. */
     sum += in;
-    sumOfSquares += ((q63_t) (in) * (in));
+
     in = *pSrc++ >> 8U;
-    sum += in;
     sumOfSquares += ((q63_t) (in) * (in));
-    in = *pSrc++ >> 8U;
     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++ >> 8U;
+    sumOfSquares += ((q63_t) (in) * (in));
     sum += in;
+
+    in = *pSrc++ >> 8U;
     sumOfSquares += ((q63_t) (in) * (in));
+    sum += in;
 
-    /* Decrement the loop counter */
+    /* Decrement loop counter */
     blkCnt--;
   }
 
-  /* Compute Mean of squares of the input samples
-   * and then store the result in a temporary variable, meanOfSquares. */
-  meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1U);
+  /* Loop unrolling: Compute remaining outputs */
+  blkCnt = blockSize % 0x4U;
 
 #else
-  /* Run the below code for Cortex-M0 */
 
-  /* Loop over blockSize number of values */
+  /* Initialize blkCnt with number of samples */
   blkCnt = blockSize;
 
+#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
+
   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. */
+    /* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */
+    /* C = A[0] + A[1] + ... + A[blockSize-1] */
+
     in = *pSrc++ >> 8U;
+    /* Compute sum of squares and store result in a temporary variable, sumOfSquares. */
     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. */
+    /* Compute sum and store result in a temporary variable, sum. */
     sum += in;
 
-    /* Decrement the loop counter */
+    /* Decrement loop counter */
     blkCnt--;
   }
 
-  /* Compute Mean of squares of the input samples
-   * and then store the result in a temporary variable, meanOfSquares. */
-  meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1U);
-
-#endif /* #if defined (ARM_MATH_DSP) */
+  /* Compute Mean of squares and store result in a temporary variable, meanOfSquares. */
+  meanOfSquares = (sumOfSquares / (q63_t)(blockSize - 1U));
 
   /* Compute square of mean */
-  squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1U));
+  squareOfMean = ( sum * sum / (q63_t)(blockSize * (blockSize - 1U)));
 
-  /* Compute standard deviation and then store the result to the destination */
+  /* Compute standard deviation and store result in destination */
   arm_sqrt_q31((meanOfSquares - squareOfMean) >> 15U, pResult);
 }
 
 /**
- * @} end of STD group
+  @} end of STD group
  */