Diff: DSP/source/StatisticsFunctions/arm_var_q31.c

Revision:

0:eedb7d567a5d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DSP/source/StatisticsFunctions/arm_var_q31.c	Thu Apr 12 01:31:58 2018 +0000
@@ -0,0 +1,170 @@
+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_var_q31.c
+ * Description:  Variance of an array of Q31 type
+ *
+ * $Date:        27. January 2017
+ * $Revision:    V.1.5.1
+ *
+ * Target Processor: Cortex-M cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "arm_math.h"
+
+/**
+ * @ingroup groupStats
+ */
+
+/**
+ * @addtogroup variance
+ * @{
+ */
+
+/**
+ * @brief Variance 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 variance 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.
+ *
+ */
+
+void arm_var_q31(
+  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 */
+
+  if (blockSize == 1U)
+  {
+    *pResult = 0;
+    return;
+  }
+
+#if defined (ARM_MATH_DSP)
+  /* 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++ >> 8U;
+    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));
+    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;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* Decrement the 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);
+
+#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++ >> 8U;
+    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. */
+  meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1U);
+
+#endif /* #if defined (ARM_MATH_DSP) */
+
+  /* Compute square of mean */
+  squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1U));
+
+  /* Compute standard deviation and then store the result to the destination */
+  *pResult = (meanOfSquares - squareOfMean) >> 15U;
+}
+
+/**
+ * @} end of variance group
+ */
+