| /* ---------------------------------------------------------------------- |
| * Project: CMSIS DSP Library |
| * Title: arm_std_f32.c |
| * Description: Standard deviation of the elements of a floating-point 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 |
| */ |
| |
| /** |
| * @defgroup STD Standard deviation |
| * |
| * Calculates the standard deviation of the elements in the input vector. |
| * The underlying algorithm is used: |
| * |
| * <pre> |
| * Result = sqrt((sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1)) |
| * |
| * where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1] |
| * |
| * sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1] |
| * </pre> |
| * |
| * There are separate functions for floating point, Q31, and Q15 data types. |
| */ |
| |
| /** |
| * @addtogroup STD |
| * @{ |
| */ |
| |
| |
| /** |
| * @brief Standard deviation of the elements of a floating-point 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. |
| */ |
| |
| void arm_std_f32( |
| float32_t * pSrc, |
| uint32_t blockSize, |
| float32_t * pResult) |
| { |
| float32_t sum = 0.0f; /* Temporary result storage */ |
| float32_t sumOfSquares = 0.0f; /* Sum of squares */ |
| float32_t in; /* input value */ |
| uint32_t blkCnt; /* loop counter */ |
| #if defined (ARM_MATH_DSP) |
| float32_t meanOfSquares, mean, squareOfMean; /* Temporary variables */ |
| #else |
| float32_t squareOfSum; /* Square of Sum */ |
| float32_t var; /* Temporary varaince storage */ |
| #endif |
| |
| 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++; |
| sum += in; |
| sumOfSquares += in * in; |
| in = *pSrc++; |
| sum += in; |
| sumOfSquares += in * in; |
| in = *pSrc++; |
| sum += in; |
| sumOfSquares += in * in; |
| in = *pSrc++; |
| sum += in; |
| sumOfSquares += 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++; |
| sum += in; |
| sumOfSquares += 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 / ((float32_t) blockSize - 1.0f); |
| |
| /* Compute mean of all input values */ |
| mean = sum / (float32_t) blockSize; |
| |
| /* Compute square of mean */ |
| squareOfMean = (mean * mean) * (((float32_t) blockSize) / |
| ((float32_t) blockSize - 1.0f)); |
| |
| /* Compute standard deviation and then store the result to the destination */ |
| arm_sqrt_f32((meanOfSquares - squareOfMean), pResult); |
| |
| #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++; |
| sumOfSquares += in * in; |
| |
| /* C = (A[0] + A[1] + ... + A[blockSize-1]) */ |
| /* Compute Sum of the input samples |
| * and then store the result in a temporary variable, sum. */ |
| sum += in; |
| |
| /* Decrement the loop counter */ |
| blkCnt--; |
| } |
| |
| /* Compute the square of sum */ |
| squareOfSum = ((sum * sum) / (float32_t) blockSize); |
| |
| /* Compute the variance */ |
| var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f)); |
| |
| /* Compute standard deviation and then store the result to the destination */ |
| arm_sqrt_f32(var, pResult); |
| |
| #endif /* #if defined (ARM_MATH_DSP) */ |
| } |
| |
| /** |
| * @} end of STD group |
| */ |