pigweed / third_party / github / STMicroelectronics / cmsis_core / 7dd288b23bf605a3a2fafa81a29d2c96a2fd83ce / . / DSP_Lib / Source / StatisticsFunctions / arm_mean_q15.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_mean_q15.c | |

* | |

* Description: Mean value of a Q15 vector. | |

* | |

* 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; | |

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

#include "arm_math.h" | |

/** | |

* @ingroup groupStats | |

*/ | |

/** | |

* @addtogroup mean | |

* @{ | |

*/ | |

/** | |

* @brief Mean value of a Q15 vector. | |

* @param[in] *pSrc points to the input vector | |

* @param[in] blockSize length of the input vector | |

* @param[out] *pResult mean value returned here | |

* @return none. | |

* | |

* @details | |

* <b>Scaling and Overflow Behavior:</b> | |

* \par | |

* The function is implemented using a 32-bit internal accumulator. | |

* The input is represented in 1.15 format and is accumulated in a 32-bit | |

* accumulator in 17.15 format. | |

* There is no risk of internal overflow with this approach, and the | |

* full precision of intermediate result is preserved. | |

* Finally, the accumulator is saturated and truncated to yield a result of 1.15 format. | |

* | |

*/ | |

void arm_mean_q15( | |

q15_t * pSrc, | |

uint32_t blockSize, | |

q15_t * pResult) | |

{ | |

q31_t sum = 0; /* Temporary result storage */ | |

uint32_t blkCnt; /* loop counter */ | |

#ifndef ARM_MATH_CM0_FAMILY | |

/* Run the below code for Cortex-M4 and Cortex-M3 */ | |

q31_t in; | |

/*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[1] + A[2] + ... + A[blockSize-1]) */ | |

in = *__SIMD32(pSrc)++; | |

sum += ((in << 16) >> 16); | |

sum += (in >> 16); | |

in = *__SIMD32(pSrc)++; | |

sum += ((in << 16) >> 16); | |

sum += (in >> 16); | |

/* 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; | |

#else | |

/* Run the below code for Cortex-M0 */ | |

/* Loop over blockSize number of values */ | |

blkCnt = blockSize; | |

#endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |

while(blkCnt > 0u) | |

{ | |

/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ | |

sum += *pSrc++; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) / blockSize */ | |

/* Store the result to the destination */ | |

*pResult = (q15_t) (sum / (q31_t)blockSize); | |

} | |

/** | |

* @} end of mean group | |

*/ |