| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_std_q31.c |
| * Description: Standard deviation 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 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. |
| * |
| */ |
| |
| void arm_std_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 */ |
| arm_sqrt_q31((meanOfSquares - squareOfMean) >> 15U, pResult); |
| } |
| |
| /** |
| * @} end of STD group |
| */ |