| 提交 | 用户 | age | ||
| bfc108 | 1 | /* ---------------------------------------------------------------------- |
| Q | 2 | * Copyright (C) 2010-2014 ARM Limited. All rights reserved. |
| 3 | * | |
| 4 | * $Date: 19. March 2015 | |
| 5 | * $Revision: V.1.4.5 | |
| 6 | * | |
| 7 | * Project: CMSIS DSP Library | |
| 8 | * Title: arm_std_q31.c | |
| 9 | * | |
| 10 | * Description: Standard deviation of an array of Q31 type. | |
| 11 | * | |
| 12 | * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 | |
| 13 | * | |
| 14 | * Redistribution and use in source and binary forms, with or without | |
| 15 | * modification, are permitted provided that the following conditions | |
| 16 | * are met: | |
| 17 | * - Redistributions of source code must retain the above copyright | |
| 18 | * notice, this list of conditions and the following disclaimer. | |
| 19 | * - Redistributions in binary form must reproduce the above copyright | |
| 20 | * notice, this list of conditions and the following disclaimer in | |
| 21 | * the documentation and/or other materials provided with the | |
| 22 | * distribution. | |
| 23 | * - Neither the name of ARM LIMITED nor the names of its contributors | |
| 24 | * may be used to endorse or promote products derived from this | |
| 25 | * software without specific prior written permission. | |
| 26 | * | |
| 27 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
| 28 | * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
| 29 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS | |
| 30 | * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE | |
| 31 | * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, | |
| 32 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, | |
| 33 | * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; | |
| 34 | * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER | |
| 35 | * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
| 36 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN | |
| 37 | * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE | |
| 38 | * POSSIBILITY OF SUCH DAMAGE. | |
| 39 | * -------------------------------------------------------------------- */ | |
| 40 | ||
| 41 | #include "arm_math.h" | |
| 42 | ||
| 43 | /** | |
| 44 | * @ingroup groupStats | |
| 45 | */ | |
| 46 | ||
| 47 | /** | |
| 48 | * @addtogroup STD | |
| 49 | * @{ | |
| 50 | */ | |
| 51 | ||
| 52 | ||
| 53 | /** | |
| 54 | * @brief Standard deviation of the elements of a Q31 vector. | |
| 55 | * @param[in] *pSrc points to the input vector | |
| 56 | * @param[in] blockSize length of the input vector | |
| 57 | * @param[out] *pResult standard deviation value returned here | |
| 58 | * @return none. | |
| 59 | * @details | |
| 60 | * <b>Scaling and Overflow Behavior:</b> | |
| 61 | * | |
| 62 | *\par | |
| 63 | * The function is implemented using an internal 64-bit accumulator. | |
| 64 | * The input is represented in 1.31 format, which is then downshifted by 8 bits | |
| 65 | * which yields 1.23, and intermediate multiplication yields a 2.46 format. | |
| 66 | * The accumulator maintains full precision of the intermediate multiplication results, | |
| 67 | * but provides only a 16 guard bits. | |
| 68 | * There is no saturation on intermediate additions. | |
| 69 | * If the accumulator overflows it wraps around and distorts the result. | |
| 70 | * In order to avoid overflows completely the input signal must be scaled down by | |
| 71 | * log2(blockSize)-8 bits, as a total of blockSize additions are performed internally. | |
| 72 | * After division, internal variables should be Q18.46 | |
| 73 | * Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value. | |
| 74 | * | |
| 75 | */ | |
| 76 | ||
| 77 | ||
| 78 | void arm_std_q31( | |
| 79 | q31_t * pSrc, | |
| 80 | uint32_t blockSize, | |
| 81 | q31_t * pResult) | |
| 82 | { | |
| 83 | q63_t sum = 0; /* Accumulator */ | |
| 84 | q63_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ | |
| 85 | q31_t in; /* input value */ | |
| 86 | uint32_t blkCnt; /* loop counter */ | |
| 87 | q63_t sumOfSquares = 0; /* Accumulator */ | |
| 88 | ||
| 89 | if(blockSize == 1) | |
| 90 | { | |
| 91 | *pResult = 0; | |
| 92 | return; | |
| 93 | } | |
| 94 | ||
| 95 | #ifndef ARM_MATH_CM0_FAMILY | |
| 96 | ||
| 97 | /* Run the below code for Cortex-M4 and Cortex-M3 */ | |
| 98 | ||
| 99 | /*loop Unrolling */ | |
| 100 | blkCnt = blockSize >> 2u; | |
| 101 | ||
| 102 | /* First part of the processing with loop unrolling. Compute 4 outputs at a time. | |
| 103 | ** a second loop below computes the remaining 1 to 3 samples. */ | |
| 104 | while(blkCnt > 0u) | |
| 105 | { | |
| 106 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ | |
| 107 | /* Compute Sum of squares of the input samples | |
| 108 | * and then store the result in a temporary variable, sum. */ | |
| 109 | in = *pSrc++ >> 8; | |
| 110 | sum += in; | |
| 111 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 112 | in = *pSrc++ >> 8; | |
| 113 | sum += in; | |
| 114 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 115 | in = *pSrc++ >> 8; | |
| 116 | sum += in; | |
| 117 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 118 | in = *pSrc++ >> 8; | |
| 119 | sum += in; | |
| 120 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 121 | ||
| 122 | /* Decrement the loop counter */ | |
| 123 | blkCnt--; | |
| 124 | } | |
| 125 | ||
| 126 | /* If the blockSize is not a multiple of 4, compute any remaining output samples here. | |
| 127 | ** No loop unrolling is used. */ | |
| 128 | blkCnt = blockSize % 0x4u; | |
| 129 | ||
| 130 | while(blkCnt > 0u) | |
| 131 | { | |
| 132 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ | |
| 133 | /* Compute Sum of squares of the input samples | |
| 134 | * and then store the result in a temporary variable, sum. */ | |
| 135 | in = *pSrc++ >> 8; | |
| 136 | sum += in; | |
| 137 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 138 | ||
| 139 | /* Decrement the loop counter */ | |
| 140 | blkCnt--; | |
| 141 | } | |
| 142 | ||
| 143 | /* Compute Mean of squares of the input samples | |
| 144 | * and then store the result in a temporary variable, meanOfSquares. */ | |
| 145 | meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1); | |
| 146 | ||
| 147 | #else | |
| 148 | ||
| 149 | /* Run the below code for Cortex-M0 */ | |
| 150 | ||
| 151 | /* Loop over blockSize number of values */ | |
| 152 | blkCnt = blockSize; | |
| 153 | ||
| 154 | while(blkCnt > 0u) | |
| 155 | { | |
| 156 | /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ | |
| 157 | /* Compute Sum of squares of the input samples | |
| 158 | * and then store the result in a temporary variable, sumOfSquares. */ | |
| 159 | in = *pSrc++ >> 8; | |
| 160 | sumOfSquares += ((q63_t) (in) * (in)); | |
| 161 | ||
| 162 | /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ | |
| 163 | /* Compute sum of all input values and then store the result in a temporary variable, sum. */ | |
| 164 | sum += in; | |
| 165 | ||
| 166 | /* Decrement the loop counter */ | |
| 167 | blkCnt--; | |
| 168 | } | |
| 169 | ||
| 170 | /* Compute Mean of squares of the input samples | |
| 171 | * and then store the result in a temporary variable, meanOfSquares. */ | |
| 172 | meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1); | |
| 173 | ||
| 174 | #endif /* #ifndef ARM_MATH_CM0_FAMILY */ | |
| 175 | ||
| 176 | /* Compute square of mean */ | |
| 177 | squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1u)); | |
| 178 | ||
| 179 | /* Compute standard deviation and then store the result to the destination */ | |
| 180 | arm_sqrt_q31((meanOfSquares - squareOfMean) >> 15, pResult); | |
| 181 | ||
| 182 | } | |
| 183 | ||
| 184 | /** | |
| 185 | * @} end of STD group | |
| 186 | */ | |
