pigweed / third_party / github / STMicroelectronics / cmsis_core / cb6d9400754e6c9050487dfa573949b61152ac99 / . / 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: 27. January 2017 | |

* $Revision: V.1.5.1 | |

* | |

* Target Processor: Cortex-M cores | |

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

/* | |

* Copyright (C) 2010-2017 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" | |

/** | |

* @addtogroup RMS | |

* @{ | |

*/ | |

/** | |

* @brief Root Mean Square 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 rms 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_rms_q31( | |

q31_t * pSrc, | |

uint32_t blockSize, | |

q31_t * pResult) | |

{ | |

q63_t sum = 0; /* accumulator */ | |

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

uint32_t blkCnt; /* loop counter */ | |

#if defined (ARM_MATH_DSP) | |

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

q31_t in1, in2, in3, in4; /* Temporary input variables */ | |

/*loop Unrolling */ | |

blkCnt = blockSize >> 2U; | |

/* First part of the processing with loop unrolling. Compute 8 outputs at a time. | |

** a second loop below computes the remaining 1 to 7 samples. */ | |

while (blkCnt > 0U) | |

{ | |

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

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

/* read two samples from source buffer */ | |

in1 = pSrc[0]; | |

in2 = pSrc[1]; | |

/* calculate power and accumulate to accumulator */ | |

sum += (q63_t) in1 *in1; | |

sum += (q63_t) in2 *in2; | |

/* read two samples from source buffer */ | |

in3 = pSrc[2]; | |

in4 = pSrc[3]; | |

/* calculate power and accumulate to accumulator */ | |

sum += (q63_t) in3 *in3; | |

sum += (q63_t) in4 *in4; | |

/* update source buffer to process next samples */ | |

pSrc += 4U; | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* If the blockSize is not a multiple of 8, compute any remaining output samples here. | |

** No loop unrolling is used. */ | |

blkCnt = blockSize % 0x4U; | |

#else | |

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

blkCnt = blockSize; | |

#endif /* #if defined (ARM_MATH_DSP) */ | |

while (blkCnt > 0U) | |

{ | |

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

/* Compute sum of the squares and then store the results in a temporary variable, sum */ | |

in = *pSrc++; | |

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

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

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

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

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

} | |

/** | |

* @} end of RMS group | |

*/ |