arm_std_q31.c
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CLexer
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r41 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 15. July 2011 | ||||
* $Revision: V1.0.10 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_std_q31.c | ||||
* | ||||
* Description: Standard deviation of an array of Q31 type. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | ||||
* | ||||
* Version 1.0.10 2011/7/15 | ||||
* Big Endian support added and Merged M0 and M3/M4 Source code. | ||||
* | ||||
* Version 1.0.3 2010/11/29 | ||||
* Re-organized the CMSIS folders and updated documentation. | ||||
* | ||||
* Version 1.0.2 2010/11/11 | ||||
* Documentation updated. | ||||
* | ||||
* Version 1.0.1 2010/10/05 | ||||
* Production release and review comments incorporated. | ||||
* | ||||
* Version 1.0.0 2010/09/20 | ||||
* Production release and review comments incorporated. | ||||
* -------------------------------------------------------------------- */ | ||||
#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, and intermediate multiplication | ||||
* yields a 2.62 format. | ||||
* The accumulator maintains full precision of the intermediate multiplication results, | ||||
* but provides only a single guard bit. | ||||
* 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) bits, as a total of blockSize additions are performed internally. | ||||
* Finally, the 2.62 accumulator is right shifted by 31 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 */ | ||||
q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ | ||||
q31_t mean; /* mean */ | ||||
q31_t in; /* input value */ | ||||
q31_t t; /* Temporary variable */ | ||||
uint32_t blkCnt; /* loop counter */ | ||||
#ifndef ARM_MATH_CM0 | ||||
/* Run the below code for Cortex-M4 and Cortex-M3 */ | ||||
q31_t *pIn; /* Temporary pointer */ | ||||
pIn = pSrc; | ||||
/*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 += ((q63_t) (in) * (in)); | ||||
in = *pSrc++; | ||||
sum += ((q63_t) (in) * (in)); | ||||
in = *pSrc++; | ||||
sum += ((q63_t) (in) * (in)); | ||||
in = *pSrc++; | ||||
sum += ((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++; | ||||
sum += ((q63_t) (in) * (in)); | ||||
/* Decrement the loop counter */ | ||||
blkCnt--; | ||||
} | ||||
t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); | ||||
/* Compute Mean of squares of the input samples | ||||
* and then store the result in a temporary variable, meanOfSquares. */ | ||||
sum = (sum >> 31); | ||||
meanOfSquares = (q31_t) ((sum * t) >> 30); | ||||
/* Reset the accumulator */ | ||||
sum = 0; | ||||
/*loop Unrolling */ | ||||
blkCnt = blockSize >> 2u; | ||||
/* Reset the input working pointer */ | ||||
pSrc = pIn; | ||||
/* 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[1] + A[2] + ... + A[blockSize-1]) */ | ||||
/* Compute sum of all input values and then store the result in a temporary variable, sum. */ | ||||
sum += *pSrc++; | ||||
sum += *pSrc++; | ||||
sum += *pSrc++; | ||||
sum += *pSrc++; | ||||
/* 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[1] + A[2] + ... + A[blockSize-1]) */ | ||||
/* Compute sum of all input values and then store the result in a temporary variable, sum. */ | ||||
sum += *pSrc++; | ||||
/* Decrement the loop counter */ | ||||
blkCnt--; | ||||
} | ||||
#else | ||||
/* Run the below code for Cortex-M0 */ | ||||
q63_t sumOfSquares = 0; /* Accumulator */ | ||||
/* 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 += ((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. */ | ||||
t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); | ||||
sumOfSquares = (sumOfSquares >> 31); | ||||
meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30); | ||||
#endif /* #ifndef ARM_MATH_CM0 */ | ||||
/* Compute mean of all input values */ | ||||
t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f); | ||||
mean = (q31_t) (sum); | ||||
/* Compute square of mean */ | ||||
squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31); | ||||
squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31); | ||||
/* Compute standard deviation and then store the result to the destination */ | ||||
arm_sqrt_q31(meanOfSquares - squareOfMean, pResult); | ||||
} | ||||
/** | ||||
* @} end of STD group | ||||
*/ | ||||