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Drivers/CMSIS/DSP/Source/StatisticsFunctions/arm_power_q31.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_power_q31.c
+ * Description:  Sum of the squares of the elements of a Q31 vector
+ *
+ * $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 power
+ * @{
+ */
+
+/**
+ * @brief Sum of the squares 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 sum of the squares 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 1.31 format.
+ * Intermediate multiplication yields a 2.62 format, and this
+ * result is truncated to 2.48 format by discarding the lower 14 bits.
+ * The 2.48 result is then added without saturation to a 64-bit accumulator in 16.48 format.
+ * With 15 guard bits in the accumulator, there is no risk of overflow, and the
+ * full precision of the intermediate multiplication is preserved.
+ * Finally, the return result is in 16.48 format.
+ *
+ */
+
+void arm_power_q31(
+  q31_t * pSrc,
+  uint32_t blockSize,
+  q63_t * pResult)
+{
+  q63_t sum = 0;                                 /* Temporary result storage */
+  q31_t in;
+  uint32_t blkCnt;                               /* loop counter */
+
+
+#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[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
+    /* Compute Power then shift intermediate results by 14 bits to maintain 16.48 format and then store the result in a temporary variable sum, providing 15 guard bits. */
+    in = *pSrc++;
+    sum += ((q63_t) in * in) >> 14U;
+
+    in = *pSrc++;
+    sum += ((q63_t) in * in) >> 14U;
+
+    in = *pSrc++;
+    sum += ((q63_t) in * in) >> 14U;
+
+    in = *pSrc++;
+    sum += ((q63_t) in * in) >> 14U;
+
+    /* 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;
+
+#else
+  /* Run the below code for Cortex-M0 */
+
+  /* Loop over blockSize number of values */
+  blkCnt = blockSize;
+
+#endif /* #if defined (ARM_MATH_DSP) */
+
+  while (blkCnt > 0U)
+  {
+    /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */
+    /* Compute Power and then store the result in a temporary variable, sum. */
+    in = *pSrc++;
+    sum += ((q63_t) in * in) >> 14U;
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* Store the results in 16.48 format  */
+  *pResult = sum;
+}
+
+/**
+ * @} end of power group
+ */