/* ---------------------------------------------------------------------- * Project: CMSIS DSP Library * Title: arm_var_f32.c * Description: Variance of the elements of a floating-point vector * * $Date: 23 April 2021 * $Revision: V1.9.0 * * Target Processor: Cortex-M and Cortex-A cores * -------------------------------------------------------------------- */ /* * Copyright (C) 2010-2021 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 "dsp/statistics_functions.h" /** @ingroup groupStats */ /** @defgroup variance Variance Calculates the variance of the elements in the input vector. The underlying algorithm used is the direct method sometimes referred to as the two-pass method: 
      Result = sum(element - meanOfElements)^2) / numElement - 1

      meanOfElements = ( pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] ) / blockSize
There are separate functions for floating point, Q31, and Q15 data types. */ /** @addtogroup variance @{ */ /** @brief Variance 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 variance value returned here @return none */ #if defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) #include "arm_helium_utils.h" void arm_var_f32( const float32_t * pSrc, uint32_t blockSize, float32_t * pResult) { uint32_t blkCnt; /* loop counters */ f32x4_t vecSrc; f32x4_t sumVec = vdupq_n_f32(0.0f); float32_t fMean; float32_t sum = 0.0f; /* accumulator */ float32_t in; /* Temporary variable to store input value */ if (blockSize <= 1U) { *pResult = 0; return; } arm_mean_f32(pSrc, blockSize, &fMean); /* Compute 4 outputs at a time */ blkCnt = blockSize >> 2U; while (blkCnt > 0U) { vecSrc = vldrwq_f32(pSrc); /* * sum lanes */ vecSrc = vsubq(vecSrc, fMean); sumVec = vfmaq(sumVec, vecSrc, vecSrc); blkCnt --; pSrc += 4; } sum = vecAddAcrossF32Mve(sumVec); /* * tail */ blkCnt = blockSize & 0x3; while (blkCnt > 0U) { in = *pSrc++ - fMean; sum += in * in; /* Decrement loop counter */ blkCnt--; } /* Variance */ *pResult = sum / (float32_t) (blockSize - 1); } #else #if defined(ARM_MATH_NEON_EXPERIMENTAL) && !defined(ARM_MATH_AUTOVECTORIZE) void arm_var_f32( const float32_t * pSrc, uint32_t blockSize, float32_t * pResult) { float32_t mean; float32_t sum = 0.0f; /* accumulator */ float32_t in; /* Temporary variable to store input value */ uint32_t blkCnt; /* loop counter */ float32x4_t sumV = vdupq_n_f32(0.0f); /* Temporary result storage */ float32x2_t sumV2; float32x4_t inV; float32x4_t avg; arm_mean_f32(pSrc,blockSize,&mean); avg = vdupq_n_f32(mean); blkCnt = blockSize >> 2U; /* 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 and then store the result in a temporary variable, sum. */ inV = vld1q_f32(pSrc); inV = vsubq_f32(inV, avg); sumV = vmlaq_f32(sumV, inV, inV); pSrc += 4; /* Decrement the loop counter */ blkCnt--; } sumV2 = vpadd_f32(vget_low_f32(sumV),vget_high_f32(sumV)); sum = vget_lane_f32(sumV2, 0) + vget_lane_f32(sumV2, 1); /* 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[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */ /* compute power and then store the result in a temporary variable, sum. */ in = *pSrc++; in = in - mean; sum += in * in; /* Decrement the loop counter */ blkCnt--; } /* Variance */ *pResult = sum / (float32_t)(blockSize - 1.0f); } #else void arm_var_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 fSum = 0.0f; float32_t fMean, fValue; const float32_t * pInput = pSrc; if (blockSize <= 1U) { *pResult = 0; return; } #if defined (ARM_MATH_LOOPUNROLL) && !defined(ARM_MATH_AUTOVECTORIZE) /* Loop unrolling: Compute 4 outputs at a time */ blkCnt = blockSize >> 2U; while (blkCnt > 0U) { /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ sum += *pInput++; sum += *pInput++; sum += *pInput++; sum += *pInput++; /* 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[1] + A[2] + ... + A[blockSize-1]) */ sum += *pInput++; /* Decrement loop counter */ blkCnt--; } /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize */ fMean = sum / (float32_t) blockSize; pInput = pSrc; #if defined (ARM_MATH_LOOPUNROLL) && !defined(ARM_MATH_AUTOVECTORIZE) /* Loop unrolling: Compute 4 outputs at a time */ blkCnt = blockSize >> 2U; while (blkCnt > 0U) { fValue = *pInput++ - fMean; fSum += fValue * fValue; fValue = *pInput++ - fMean; fSum += fValue * fValue; fValue = *pInput++ - fMean; fSum += fValue * fValue; fValue = *pInput++ - fMean; fSum += fValue * fValue; /* 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) { fValue = *pInput++ - fMean; fSum += fValue * fValue; /* Decrement loop counter */ blkCnt--; } /* Variance */ *pResult = fSum / (float32_t)(blockSize - 1.0f); } #endif /* #if defined(ARM_MATH_NEON) */ #endif /* defined(ARM_MATH_MVEF) && !defined(ARM_MATH_AUTOVECTORIZE) */ /** @} end of variance group */