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CMSIS DSP Lib

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cmsis_dsp/StatisticsFunctions/arm_std_q31.c@1:fdd22bb7aa52, 2012-11-28 (annotated)

Committer:
emilmont
Date:
Wed Nov 28 12:30:09 2012 +0000
Revision:
1:fdd22bb7aa52
Child:
2:da51fb522205
DSP library code

Who changed what in which revision?

UserRevisionLine numberNew contents of line
emilmont 1:fdd22bb7aa52 1 /* ----------------------------------------------------------------------
emilmont 1:fdd22bb7aa52 2 * Copyright (C) 2010 ARM Limited. All rights reserved.
emilmont 1:fdd22bb7aa52 3 *
emilmont 1:fdd22bb7aa52 4 * $Date: 15. February 2012
emilmont 1:fdd22bb7aa52 5 * $Revision: V1.1.0
emilmont 1:fdd22bb7aa52 6 *
emilmont 1:fdd22bb7aa52 7 * Project: CMSIS DSP Library
emilmont 1:fdd22bb7aa52 8 * Title: arm_std_q31.c
emilmont 1:fdd22bb7aa52 9 *
emilmont 1:fdd22bb7aa52 10 * Description: Standard deviation of an array of Q31 type.
emilmont 1:fdd22bb7aa52 11 *
emilmont 1:fdd22bb7aa52 12 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
emilmont 1:fdd22bb7aa52 13 *
emilmont 1:fdd22bb7aa52 14 * Version 1.1.0 2012/02/15
emilmont 1:fdd22bb7aa52 15 * Updated with more optimizations, bug fixes and minor API changes.
emilmont 1:fdd22bb7aa52 16 *
emilmont 1:fdd22bb7aa52 17 * Version 1.0.10 2011/7/15
emilmont 1:fdd22bb7aa52 18 * Big Endian support added and Merged M0 and M3/M4 Source code.
emilmont 1:fdd22bb7aa52 19 *
emilmont 1:fdd22bb7aa52 20 * Version 1.0.3 2010/11/29
emilmont 1:fdd22bb7aa52 21 * Re-organized the CMSIS folders and updated documentation.
emilmont 1:fdd22bb7aa52 22 *
emilmont 1:fdd22bb7aa52 23 * Version 1.0.2 2010/11/11
emilmont 1:fdd22bb7aa52 24 * Documentation updated.
emilmont 1:fdd22bb7aa52 25 *
emilmont 1:fdd22bb7aa52 26 * Version 1.0.1 2010/10/05
emilmont 1:fdd22bb7aa52 27 * Production release and review comments incorporated.
emilmont 1:fdd22bb7aa52 28 *
emilmont 1:fdd22bb7aa52 29 * Version 1.0.0 2010/09/20
emilmont 1:fdd22bb7aa52 30 * Production release and review comments incorporated.
emilmont 1:fdd22bb7aa52 31 * -------------------------------------------------------------------- */
emilmont 1:fdd22bb7aa52 32
emilmont 1:fdd22bb7aa52 33 #include "arm_math.h"
emilmont 1:fdd22bb7aa52 34
emilmont 1:fdd22bb7aa52 35 /**
emilmont 1:fdd22bb7aa52 36 * @ingroup groupStats
emilmont 1:fdd22bb7aa52 37 */
emilmont 1:fdd22bb7aa52 38
emilmont 1:fdd22bb7aa52 39 /**
emilmont 1:fdd22bb7aa52 40 * @addtogroup STD
emilmont 1:fdd22bb7aa52 41 * @{
emilmont 1:fdd22bb7aa52 42 */
emilmont 1:fdd22bb7aa52 43
emilmont 1:fdd22bb7aa52 44
emilmont 1:fdd22bb7aa52 45 /**
emilmont 1:fdd22bb7aa52 46 * @brief Standard deviation of the elements of a Q31 vector.
emilmont 1:fdd22bb7aa52 47 * @param[in] *pSrc points to the input vector
emilmont 1:fdd22bb7aa52 48 * @param[in] blockSize length of the input vector
emilmont 1:fdd22bb7aa52 49 * @param[out] *pResult standard deviation value returned here
emilmont 1:fdd22bb7aa52 50 * @return none.
emilmont 1:fdd22bb7aa52 51 * @details
emilmont 1:fdd22bb7aa52 52 * <b>Scaling and Overflow Behavior:</b>
emilmont 1:fdd22bb7aa52 53 *
emilmont 1:fdd22bb7aa52 54 *\par
emilmont 1:fdd22bb7aa52 55 * The function is implemented using an internal 64-bit accumulator.
emilmont 1:fdd22bb7aa52 56 * The input is represented in 1.31 format, and intermediate multiplication
emilmont 1:fdd22bb7aa52 57 * yields a 2.62 format.
emilmont 1:fdd22bb7aa52 58 * The accumulator maintains full precision of the intermediate multiplication results,
emilmont 1:fdd22bb7aa52 59 * but provides only a single guard bit.
emilmont 1:fdd22bb7aa52 60 * There is no saturation on intermediate additions.
emilmont 1:fdd22bb7aa52 61 * If the accumulator overflows it wraps around and distorts the result.
emilmont 1:fdd22bb7aa52 62 * In order to avoid overflows completely the input signal must be scaled down by
emilmont 1:fdd22bb7aa52 63 * log2(blockSize) bits, as a total of blockSize additions are performed internally.
emilmont 1:fdd22bb7aa52 64 * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.
emilmont 1:fdd22bb7aa52 65 *
emilmont 1:fdd22bb7aa52 66 */
emilmont 1:fdd22bb7aa52 67
emilmont 1:fdd22bb7aa52 68
emilmont 1:fdd22bb7aa52 69 void arm_std_q31(
emilmont 1:fdd22bb7aa52 70 q31_t * pSrc,
emilmont 1:fdd22bb7aa52 71 uint32_t blockSize,
emilmont 1:fdd22bb7aa52 72 q31_t * pResult)
emilmont 1:fdd22bb7aa52 73 {
emilmont 1:fdd22bb7aa52 74 q63_t sum = 0; /* Accumulator */
emilmont 1:fdd22bb7aa52 75 q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */
emilmont 1:fdd22bb7aa52 76 q31_t mean; /* mean */
emilmont 1:fdd22bb7aa52 77 q31_t in; /* input value */
emilmont 1:fdd22bb7aa52 78 q31_t t; /* Temporary variable */
emilmont 1:fdd22bb7aa52 79 uint32_t blkCnt; /* loop counter */
emilmont 1:fdd22bb7aa52 80 q63_t sumOfSquares = 0; /* Accumulator */
emilmont 1:fdd22bb7aa52 81
emilmont 1:fdd22bb7aa52 82 #ifndef ARM_MATH_CM0
emilmont 1:fdd22bb7aa52 83
emilmont 1:fdd22bb7aa52 84 /* Run the below code for Cortex-M4 and Cortex-M3 */
emilmont 1:fdd22bb7aa52 85
emilmont 1:fdd22bb7aa52 86 /*loop Unrolling */
emilmont 1:fdd22bb7aa52 87 blkCnt = blockSize >> 2u;
emilmont 1:fdd22bb7aa52 88
emilmont 1:fdd22bb7aa52 89 /* First part of the processing with loop unrolling. Compute 4 outputs at a time.
emilmont 1:fdd22bb7aa52 90 ** a second loop below computes the remaining 1 to 3 samples. */
emilmont 1:fdd22bb7aa52 91 while(blkCnt > 0u)
emilmont 1:fdd22bb7aa52 92 {
emilmont 1:fdd22bb7aa52 93 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 94 /* Compute Sum of squares of the input samples
emilmont 1:fdd22bb7aa52 95 * and then store the result in a temporary variable, sum. */
emilmont 1:fdd22bb7aa52 96 in = *pSrc++;
emilmont 1:fdd22bb7aa52 97 sum += in;
emilmont 1:fdd22bb7aa52 98 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 99 in = *pSrc++;
emilmont 1:fdd22bb7aa52 100 sum += in;
emilmont 1:fdd22bb7aa52 101 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 102 in = *pSrc++;
emilmont 1:fdd22bb7aa52 103 sum += in;
emilmont 1:fdd22bb7aa52 104 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 105 in = *pSrc++;
emilmont 1:fdd22bb7aa52 106 sum += in;
emilmont 1:fdd22bb7aa52 107 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 108
emilmont 1:fdd22bb7aa52 109 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 110 blkCnt--;
emilmont 1:fdd22bb7aa52 111 }
emilmont 1:fdd22bb7aa52 112
emilmont 1:fdd22bb7aa52 113 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
emilmont 1:fdd22bb7aa52 114 ** No loop unrolling is used. */
emilmont 1:fdd22bb7aa52 115 blkCnt = blockSize % 0x4u;
emilmont 1:fdd22bb7aa52 116
emilmont 1:fdd22bb7aa52 117 while(blkCnt > 0u)
emilmont 1:fdd22bb7aa52 118 {
emilmont 1:fdd22bb7aa52 119 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 120 /* Compute Sum of squares of the input samples
emilmont 1:fdd22bb7aa52 121 * and then store the result in a temporary variable, sum. */
emilmont 1:fdd22bb7aa52 122 in = *pSrc++;
emilmont 1:fdd22bb7aa52 123 sum += in;
emilmont 1:fdd22bb7aa52 124 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 125
emilmont 1:fdd22bb7aa52 126 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 127 blkCnt--;
emilmont 1:fdd22bb7aa52 128 }
emilmont 1:fdd22bb7aa52 129
emilmont 1:fdd22bb7aa52 130 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
emilmont 1:fdd22bb7aa52 131
emilmont 1:fdd22bb7aa52 132 /* Compute Mean of squares of the input samples
emilmont 1:fdd22bb7aa52 133 * and then store the result in a temporary variable, meanOfSquares. */
emilmont 1:fdd22bb7aa52 134 sumOfSquares = (sumOfSquares >> 31);
emilmont 1:fdd22bb7aa52 135 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
emilmont 1:fdd22bb7aa52 136
emilmont 1:fdd22bb7aa52 137 #else
emilmont 1:fdd22bb7aa52 138
emilmont 1:fdd22bb7aa52 139 /* Run the below code for Cortex-M0 */
emilmont 1:fdd22bb7aa52 140
emilmont 1:fdd22bb7aa52 141 /* Loop over blockSize number of values */
emilmont 1:fdd22bb7aa52 142 blkCnt = blockSize;
emilmont 1:fdd22bb7aa52 143
emilmont 1:fdd22bb7aa52 144 while(blkCnt > 0u)
emilmont 1:fdd22bb7aa52 145 {
emilmont 1:fdd22bb7aa52 146 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 147 /* Compute Sum of squares of the input samples
emilmont 1:fdd22bb7aa52 148 * and then store the result in a temporary variable, sumOfSquares. */
emilmont 1:fdd22bb7aa52 149 in = *pSrc++;
emilmont 1:fdd22bb7aa52 150 sumOfSquares += ((q63_t) (in) * (in));
emilmont 1:fdd22bb7aa52 151
emilmont 1:fdd22bb7aa52 152 /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 153 /* Compute sum of all input values and then store the result in a temporary variable, sum. */
emilmont 1:fdd22bb7aa52 154 sum += in;
emilmont 1:fdd22bb7aa52 155
emilmont 1:fdd22bb7aa52 156 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 157 blkCnt--;
emilmont 1:fdd22bb7aa52 158 }
emilmont 1:fdd22bb7aa52 159
emilmont 1:fdd22bb7aa52 160 /* Compute Mean of squares of the input samples
emilmont 1:fdd22bb7aa52 161 * and then store the result in a temporary variable, meanOfSquares. */
emilmont 1:fdd22bb7aa52 162 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
emilmont 1:fdd22bb7aa52 163 sumOfSquares = (sumOfSquares >> 31);
emilmont 1:fdd22bb7aa52 164 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30);
emilmont 1:fdd22bb7aa52 165
emilmont 1:fdd22bb7aa52 166 #endif /* #ifndef ARM_MATH_CM0 */
emilmont 1:fdd22bb7aa52 167
emilmont 1:fdd22bb7aa52 168 /* Compute mean of all input values */
emilmont 1:fdd22bb7aa52 169 t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
emilmont 1:fdd22bb7aa52 170 mean = (q31_t) (sum);
emilmont 1:fdd22bb7aa52 171
emilmont 1:fdd22bb7aa52 172 /* Compute square of mean */
emilmont 1:fdd22bb7aa52 173 squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
emilmont 1:fdd22bb7aa52 174 squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
emilmont 1:fdd22bb7aa52 175
emilmont 1:fdd22bb7aa52 176
emilmont 1:fdd22bb7aa52 177 /* Compute standard deviation and then store the result to the destination */
emilmont 1:fdd22bb7aa52 178 arm_sqrt_q31(meanOfSquares - squareOfMean, pResult);
emilmont 1:fdd22bb7aa52 179
emilmont 1:fdd22bb7aa52 180 }
emilmont 1:fdd22bb7aa52 181
emilmont 1:fdd22bb7aa52 182 /**
emilmont 1:fdd22bb7aa52 183 * @} end of STD group
emilmont 1:fdd22bb7aa52 184 */