pigweed / third_party / github / STMicroelectronics / cmsis_core / 7dd288b23bf605a3a2fafa81a29d2c96a2fd83ce / . / DSP_Lib / Source / StatisticsFunctions / arm_rms_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_rms_q15.c | |

* | |

* Description: Root Mean Square of the elements 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 | |

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

#include "arm_math.h" | |

/** | |

* @addtogroup RMS | |

* @{ | |

*/ | |

/** | |

* @brief Root Mean Square 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 rms 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_rms_q15( | |

q15_t * pSrc, | |

uint32_t blockSize, | |

q15_t * pResult) | |

{ | |

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

#ifndef ARM_MATH_CM0_FAMILY | |

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

q31_t in; /* temporary variable to store the input value */ | |

q15_t in1; /* temporary variable to store the input value */ | |

uint32_t blkCnt; /* loop counter */ | |

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

in1 = *pSrc++; | |

sum = __SMLALD(in1, in1, sum); | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* Truncating and saturating the accumulator to 1.15 format */ | |

/* Store the result in the destination */ | |

arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult); | |

#else | |

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

q15_t in; /* temporary variable to store the input value */ | |

uint32_t blkCnt; /* loop counter */ | |

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

blkCnt = blockSize; | |

while(blkCnt > 0u) | |

{ | |

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

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

in = *pSrc++; | |

sum += ((q31_t) in * in); | |

/* Decrement the loop counter */ | |

blkCnt--; | |

} | |

/* Truncating and saturating the accumulator to 1.15 format */ | |

/* Store the result in the destination */ | |

arm_sqrt_q15(__SSAT((sum / (q63_t)blockSize) >> 15, 16), pResult); | |

#endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |

} | |

/** | |

* @} end of RMS group | |

*/ |