/* ---------------------------------------------------------------------- * Project: CMSIS DSP Library * Title: arm_std_f32.c * Description: Standard deviation of the elements of a floating-point vector * * $Date: 18. March 2019 * $Revision: V1.6.0 * * Target Processor: Cortex-M cores * -------------------------------------------------------------------- */ /* * Copyright (C) 2010-2019 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:
      Result = sqrt((sumOfSquares - sum2 / blockSize) / (blockSize - 1))

      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]
  
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 number of samples in input vector @param[out] pResult standard deviation value returned here @return none */ #if defined(ARM_MATH_NEON_EXPERIMENTAL) void arm_std_f32( const float32_t * pSrc, uint32_t blockSize, float32_t * pResult) { float32_t var; arm_var_f32(pSrc,blockSize,&var); arm_sqrt_f32(var, pResult); } #else void arm_std_f32( const float32_t * pSrc, uint32_t blockSize, float32_t * pResult) { uint32_t blkCnt; /* Loop counter */ float32_t sum = 0.0f; /* Temporary result storage */ float32_t sumOfSquares = 0.0f; /* Sum of squares */ float32_t in; /* Temporary variable to store input value */ #ifndef ARM_MATH_CM0_FAMILY 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_LOOPUNROLL) /* Loop unrolling: Compute 4 outputs at a time */ blkCnt = blockSize >> 2U; while (blkCnt > 0U) { /* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */ /* C = A[0] + A[1] + ... + A[blockSize-1] */ in = *pSrc++; /* Compute sum of squares and store result in a temporary variable, sumOfSquares. */ sumOfSquares += in * in; /* Compute sum and store result in a temporary variable, sum. */ sum += in; in = *pSrc++; sumOfSquares += in * in; sum += in; in = *pSrc++; sumOfSquares += in * in; sum += in; in = *pSrc++; sumOfSquares += in * in; sum += in; /* Decrement loop counter */ blkCnt--; } /* Loop unrolling: Compute remaining outputs */ blkCnt = blockSize % 0x4U; #else /* Initialize blkCnt with number of samples */ blkCnt = blockSize; #endif /* #if defined (ARM_MATH_LOOPUNROLL) */ while (blkCnt > 0U) { /* C = A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */ /* C = A[0] + A[1] + ... + A[blockSize-1] */ in = *pSrc++; /* Compute sum of squares and store result in a temporary variable, sumOfSquares. */ sumOfSquares += ( in * in); /* Compute sum and store result in a temporary variable, sum. */ sum += in; /* Decrement loop counter */ blkCnt--; } #ifndef ARM_MATH_CM0_FAMILY /* Compute Mean of squares and store 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 store result to destination */ arm_sqrt_f32((meanOfSquares - squareOfMean), pResult); #else /* Run the below code for Cortex-M0 */ /* Compute square of sum */ squareOfSum = ((sum * sum) / (float32_t) blockSize); /* Compute variance */ var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f)); /* Compute standard deviation and store result in destination */ arm_sqrt_f32(var, pResult); #endif /* #ifndef ARM_MATH_CM0_FAMILY */ } #endif /* #if defined(ARM_MATH_NEON) */ /** @} end of STD group */