pigweed / third_party / github / STMicroelectronics / cmsis_core / be0e91fb4ba19a2ee427ba8b6b75b43eb02b2810 / . / DSP / Source / StatisticsFunctions / arm_mean_q7.c

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

* Project: CMSIS DSP Library | |

* Title: arm_mean_q7.c | |

* Description: Mean value of a Q7 vector | |

* | |

* $Date: 18. March 2019 | |

* $Revision: V1.6.0 | |

* | |

* Target Processor: Cortex-M cores | |

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

/* | |

* Copyright (C) 2010-2019 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 "arm_math.h" | |

/** | |

@ingroup groupStats | |

*/ | |

/** | |

@addtogroup mean | |

@{ | |

*/ | |

/** | |

@brief Mean value of a Q7 vector. | |

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

@param[in] blockSize number of samples in input vector | |

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

@return none | |

@par Scaling and Overflow Behavior | |

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

The input is represented in 1.7 format and is accumulated in a 32-bit | |

accumulator in 25.7 format. | |

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

full precision of intermediate result is preserved. | |

Finally, the accumulator is truncated to yield a result of 1.7 format. | |

*/ | |

void arm_mean_q7( | |

const q7_t * pSrc, | |

uint32_t blockSize, | |

q7_t * pResult) | |

{ | |

uint32_t blkCnt; /* Loop counter */ | |

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

#if defined (ARM_MATH_LOOPUNROLL) | |

q31_t in; | |

#endif | |

#if defined (ARM_MATH_LOOPUNROLL) | |

/* Loop unrolling: Compute 4 outputs at a time */ | |

blkCnt = blockSize >> 2U; | |

while (blkCnt > 0U) | |

{ | |

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

in = read_q7x4_ia ((q7_t **) &pSrc); | |

sum += ((in << 24U) >> 24U); | |

sum += ((in << 16U) >> 24U); | |

sum += ((in << 8U) >> 24U); | |

sum += (in >> 24U); | |

/* Decrement the 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 += *pSrc++; | |

/* Decrement loop counter */ | |

blkCnt--; | |

} | |

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

/* Store result to destination */ | |

*pResult = (q7_t) (sum / (int32_t) blockSize); | |

} | |

/** | |

@} end of mean group | |

*/ |