pigweed / third_party / github / STMicroelectronics / cmsis_core / refs/heads/cm4 / . / DSP / Source / StatisticsFunctions / arm_rms_q31.c

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

* Project: CMSIS DSP Library | |

* Title: arm_rms_q31.c | |

* Description: Root Mean Square of the elements of a Q31 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 RMS | |

@{ | |

*/ | |

/** | |

@brief Root Mean Square of the elements of a Q31 vector. | |

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

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

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

@return none | |

@par Scaling and Overflow Behavior | |

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_rms_q31( | |

const q31_t * pSrc, | |

uint32_t blockSize, | |

q31_t * pResult) | |

{ | |

uint32_t blkCnt; /* Loop counter */ | |

uint64_t sum = 0; /* Temporary result storage (can get never negative. changed type from q63 to uint64 */ | |

q31_t in; /* Temporary variable to store input value */ | |

#if defined (ARM_MATH_LOOPUNROLL) | |

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

blkCnt = blockSize >> 2U; | |

while (blkCnt > 0U) | |

{ | |

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

in = *pSrc++; | |

/* Compute sum of squares and store result in a temporary variable, sum. */ | |

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 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[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1] */ | |

in = *pSrc++; | |

/* Compute sum of squares and store result in a temporary variable. */ | |

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

/* Decrement loop counter */ | |

blkCnt--; | |

} | |

/* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */ | |

/* Compute Rms and store result in destination vector */ | |

arm_sqrt_q31(clip_q63_to_q31((sum / (q63_t) blockSize) >> 31), pResult); | |

} | |

/** | |

@} end of RMS group | |

*/ |