arm_std_q15.c
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CLexer
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r16 | /* ---------------------------------------------------------------------- | ||
* Copyright (C) 2010 ARM Limited. All rights reserved. | ||||
* | ||||
* $Date: 29. November 2010 | ||||
* $Revision: V1.0.3 | ||||
* | ||||
* Project: CMSIS DSP Library | ||||
* Title: arm_std_q15.c | ||||
* | ||||
* Description: Standard deviation of an array of Q15 type. | ||||
* | ||||
* Target Processor: Cortex-M4/Cortex-M3 | ||||
* | ||||
* 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 Q15 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 a 64-bit internal accumulator. | ||||
* The input is represented in 1.15 format. | ||||
* Intermediate multiplication yields a 2.30 format, and this | ||||
* result is added without saturation to a 64-bit accumulator in 34.30 format. | ||||
* With 33 guard bits in the accumulator, there is no risk of overflow, and the | ||||
* full precision of the intermediate multiplication is preserved. | ||||
* Finally, the 34.30 result is truncated to 34.15 format by discarding the lower | ||||
* 15 bits, and then saturated to yield a result in 1.15 format. | ||||
*/ | ||||
void arm_std_q15( | ||||
q15_t * pSrc, | ||||
uint32_t blockSize, | ||||
q15_t * pResult) | ||||
{ | ||||
q63_t sum = 0; /* Accumulator */ | ||||
q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ | ||||
q15_t mean; /* mean */ | ||||
q31_t in; /* input value */ | ||||
q15_t in1; /* input value */ | ||||
uint32_t blkCnt; /* loop counter */ | ||||
q15_t t; /* Temporary variable */ | ||||
q15_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 = *__SIMD32(pSrc)++; | ||||
sum = __SMLALD(in, in, sum); | ||||
in = *__SIMD32(pSrc)++; | ||||
sum = __SMLALD(in, in, sum); | ||||
/* 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. */ | ||||
in1 = *pSrc++; | ||||
sum = __SMLALD(in1, in1, sum); | ||||
/* Decrement the loop counter */ | ||||
blkCnt--; | ||||
} | ||||
/* Compute Mean of squares of the input samples | ||||
* and then store the result in a temporary variable, meanOfSquares. */ | ||||
t = (q15_t) ((1.0 / (blockSize - 1)) * 16384LL); | ||||
sum = __SSAT((sum >> 15u), 16u); | ||||
meanOfSquares = (q31_t) ((sum * t) >> 14u); | ||||
/* 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--; | ||||
} | ||||
/* Compute mean of all input values */ | ||||
t = (q15_t) ((1.0 / (blockSize * (blockSize - 1))) * 32768LL); | ||||
mean = (q15_t) __SSAT(sum, 16u); | ||||
/* Compute square of mean */ | ||||
squareOfMean = ((q31_t) mean * mean) >> 15; | ||||
squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15); | ||||
/* mean of the squares minus the square of the mean. */ | ||||
in1 = (q15_t) (meanOfSquares - squareOfMean); | ||||
/* Compute standard deviation and store the result to the destination */ | ||||
arm_sqrt_q15(in1, pResult); | ||||
} | ||||
/** | ||||
* @} end of STD group | ||||
*/ | ||||