pigweed / third_party / github / STMicroelectronics / cmsis_core / 7dd288b23bf605a3a2fafa81a29d2c96a2fd83ce / . / DSP_Lib / Source / StatisticsFunctions / arm_var_q31.c

/* ---------------------------------------------------------------------- | |

* Copyright (C) 2010-2014 ARM Limited. All rights reserved. | |

* | |

* $Date: 19. March 2015 | |

* $Revision: V.1.4.5 | |

* | |

* Project: CMSIS DSP Library | |

* Title: arm_var_q31.c | |

* | |

* Description: Variance of an array of Q31 type. | |

* | |

* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | |

* | |

* Redistribution and use in source and binary forms, with or without | |

* modification, are permitted provided that the following conditions | |

* are met: | |

* - Redistributions of source code must retain the above copyright | |

* notice, this list of conditions and the following disclaimer. | |

* - Redistributions in binary form must reproduce the above copyright | |

* notice, this list of conditions and the following disclaimer in | |

* the documentation and/or other materials provided with the | |

* distribution. | |

* - Neither the name of ARM LIMITED nor the names of its contributors | |

* may be used to endorse or promote products derived from this | |

* software without specific prior written permission. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |

* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |

* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS | |

* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE | |

* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, | |

* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, | |

* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; | |

* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER | |

* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |

* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN | |

* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE | |

* POSSIBILITY OF SUCH DAMAGE. | |

* -------------------------------------------------------------------- */ | |

#include "arm_math.h" | |

/** | |

* @ingroup groupStats | |

*/ | |

/** | |

* @addtogroup variance | |

* @{ | |

*/ | |

/** | |

* @brief Variance 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 variance 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_var_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 == 1) | |

{ | |

*pResult = 0; | |

return; | |

} | |

#ifndef ARM_MATH_CM0_FAMILY | |

/* 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++ >> 8; | |

sum += in; | |

sumOfSquares += ((q63_t) (in) * (in)); | |

in = *pSrc++ >> 8; | |

sum += in; | |

sumOfSquares += ((q63_t) (in) * (in)); | |

in = *pSrc++ >> 8; | |

sum += in; | |

sumOfSquares += ((q63_t) (in) * (in)); | |

in = *pSrc++ >> 8; | |

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++ >> 8; | |

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 - 1); | |

#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++ >> 8; | |

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 - 1); | |

#endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |

/* Compute square of mean */ | |

squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1u)); | |

/* Compute standard deviation and then store the result to the destination */ | |

*pResult = (meanOfSquares - squareOfMean) >> 15; | |

} | |

/** | |

* @} end of variance group | |

*/ |