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- /* ----------------------------------------------------------------------
- * Project: CMSIS DSP Library
- * Title: arm_rms_q15.c
- * Description: Root Mean Square of the elements of a Q15 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"
- /**
- * @addtogroup RMS
- * @{
- */
- /**
- * @brief Root Mean Square 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 rms 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_rms_q15(
- q15_t * pSrc,
- uint32_t blockSize,
- q15_t * pResult)
- {
- q63_t sum = 0; /* accumulator */
- #if defined (ARM_MATH_DSP)
- /* Run the below code for Cortex-M4 and Cortex-M3 */
- q31_t in; /* temporary variable to store the input value */
- q15_t in1; /* temporary variable to store the input value */
- uint32_t blkCnt; /* loop counter */
- /* 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 the squares and then store the results 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 the squares and then store the results in a temporary variable, sum */
- in1 = *pSrc++;
- sum = __SMLALD(in1, in1, sum);
- /* Decrement the loop counter */
- blkCnt--;
- }
- /* Truncating and saturating the accumulator to 1.15 format */
- /* Store the result in the destination */
- arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
- #else
- /* Run the below code for Cortex-M0 */
- q15_t in; /* temporary variable to store the input value */
- uint32_t blkCnt; /* loop counter */
- /* 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 the squares and then store the results in a temporary variable, sum */
- in = *pSrc++;
- sum += ((q31_t) in * in);
- /* Decrement the loop counter */
- blkCnt--;
- }
- /* Truncating and saturating the accumulator to 1.15 format */
- /* Store the result in the destination */
- arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult);
- #endif /* #if defined (ARM_MATH_DSP) */
- }
- /**
- * @} end of RMS group
- */
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