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CMSIS DSP library

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cmsis_dsp/StatisticsFunctions/arm_var_q15.c@2:da51fb522205, 2013-05-30 (annotated)

Committer:
emilmont
Date:
Thu May 30 17:10:11 2013 +0100
Revision:
2:da51fb522205
Parent:
1:fdd22bb7aa52
Child:
3:7a284390b0ce
Keep "cmsis-dsp" module in synch with its source

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 2:da51fb522205 5 * $Revision: V1.1.0
emilmont 1:fdd22bb7aa52 6 *
emilmont 2:da51fb522205 7 * Project: CMSIS DSP Library
emilmont 2:da51fb522205 8 * Title: arm_var_q15.c
emilmont 1:fdd22bb7aa52 9 *
emilmont 2:da51fb522205 10 * Description: Variance of an array of Q15 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 variance
emilmont 1:fdd22bb7aa52 41 * @{
emilmont 1:fdd22bb7aa52 42 */
emilmont 1:fdd22bb7aa52 43
emilmont 1:fdd22bb7aa52 44 /**
emilmont 1:fdd22bb7aa52 45 * @brief Variance of the elements of a Q15 vector.
emilmont 1:fdd22bb7aa52 46 * @param[in] *pSrc points to the input vector
emilmont 1:fdd22bb7aa52 47 * @param[in] blockSize length of the input vector
emilmont 1:fdd22bb7aa52 48 * @param[out] *pResult variance value returned here
emilmont 1:fdd22bb7aa52 49 * @return none.
emilmont 1:fdd22bb7aa52 50 *
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 a 64-bit internal accumulator.
emilmont 1:fdd22bb7aa52 56 * The input is represented in 1.15 format.
emilmont 1:fdd22bb7aa52 57 * Intermediate multiplication yields a 2.30 format, and this
emilmont 1:fdd22bb7aa52 58 * result is added without saturation to a 64-bit accumulator in 34.30 format.
emilmont 1:fdd22bb7aa52 59 * With 33 guard bits in the accumulator, there is no risk of overflow, and the
emilmont 1:fdd22bb7aa52 60 * full precision of the intermediate multiplication is preserved.
emilmont 1:fdd22bb7aa52 61 * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
emilmont 1:fdd22bb7aa52 62 * 15 bits, and then saturated to yield a result in 1.15 format.
emilmont 1:fdd22bb7aa52 63 *
emilmont 1:fdd22bb7aa52 64 */
emilmont 1:fdd22bb7aa52 65
emilmont 1:fdd22bb7aa52 66
emilmont 1:fdd22bb7aa52 67 void arm_var_q15(
emilmont 1:fdd22bb7aa52 68 q15_t * pSrc,
emilmont 1:fdd22bb7aa52 69 uint32_t blockSize,
emilmont 1:fdd22bb7aa52 70 q31_t * pResult)
emilmont 1:fdd22bb7aa52 71 {
emilmont 1:fdd22bb7aa52 72 q31_t sum = 0; /* Accumulator */
emilmont 1:fdd22bb7aa52 73 q31_t meanOfSquares, squareOfMean; /* Mean of square and square of mean */
emilmont 1:fdd22bb7aa52 74 q15_t mean; /* mean */
emilmont 1:fdd22bb7aa52 75 uint32_t blkCnt; /* loop counter */
emilmont 1:fdd22bb7aa52 76 q15_t t; /* Temporary variable */
emilmont 1:fdd22bb7aa52 77 q63_t sumOfSquares = 0; /* Accumulator */
emilmont 1:fdd22bb7aa52 78
emilmont 1:fdd22bb7aa52 79 #ifndef ARM_MATH_CM0
emilmont 1:fdd22bb7aa52 80
emilmont 1:fdd22bb7aa52 81 /* Run the below code for Cortex-M4 and Cortex-M3 */
emilmont 1:fdd22bb7aa52 82
emilmont 1:fdd22bb7aa52 83 q31_t in; /* Input variable */
emilmont 1:fdd22bb7aa52 84 q15_t in1; /* Temporary variable */
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 = *__SIMD32(pSrc)++;
emilmont 1:fdd22bb7aa52 97 sum += ((in << 16) >> 16);
emilmont 1:fdd22bb7aa52 98 sum += (in >> 16);
emilmont 1:fdd22bb7aa52 99 sumOfSquares = __SMLALD(in, in, sumOfSquares);
emilmont 1:fdd22bb7aa52 100 in = *__SIMD32(pSrc)++;
emilmont 1:fdd22bb7aa52 101 sum += ((in << 16) >> 16);
emilmont 1:fdd22bb7aa52 102 sum += (in >> 16);
emilmont 1:fdd22bb7aa52 103 sumOfSquares = __SMLALD(in, in, sumOfSquares);
emilmont 1:fdd22bb7aa52 104
emilmont 1:fdd22bb7aa52 105 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 106 blkCnt--;
emilmont 1:fdd22bb7aa52 107 }
emilmont 1:fdd22bb7aa52 108
emilmont 1:fdd22bb7aa52 109 /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
emilmont 1:fdd22bb7aa52 110 ** No loop unrolling is used. */
emilmont 1:fdd22bb7aa52 111 blkCnt = blockSize % 0x4u;
emilmont 1:fdd22bb7aa52 112
emilmont 1:fdd22bb7aa52 113 while(blkCnt > 0u)
emilmont 1:fdd22bb7aa52 114 {
emilmont 1:fdd22bb7aa52 115 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 116 /* Compute Sum of squares of the input samples
emilmont 1:fdd22bb7aa52 117 * and then store the result in a temporary variable, sum. */
emilmont 1:fdd22bb7aa52 118 in1 = *pSrc++;
emilmont 1:fdd22bb7aa52 119 sum += in1;
emilmont 1:fdd22bb7aa52 120 sumOfSquares = __SMLALD(in1, in1, sumOfSquares);
emilmont 1:fdd22bb7aa52 121
emilmont 1:fdd22bb7aa52 122 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 123 blkCnt--;
emilmont 1:fdd22bb7aa52 124 }
emilmont 1:fdd22bb7aa52 125
emilmont 1:fdd22bb7aa52 126 /* Compute Mean of squares of the input samples
emilmont 1:fdd22bb7aa52 127 * and then store the result in a temporary variable, meanOfSquares. */
emilmont 1:fdd22bb7aa52 128 t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
emilmont 1:fdd22bb7aa52 129 sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u);
emilmont 1:fdd22bb7aa52 130
emilmont 1:fdd22bb7aa52 131 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u);
emilmont 1:fdd22bb7aa52 132
emilmont 1:fdd22bb7aa52 133 #else
emilmont 1:fdd22bb7aa52 134
emilmont 1:fdd22bb7aa52 135 /* Run the below code for Cortex-M0 */
emilmont 1:fdd22bb7aa52 136
emilmont 1:fdd22bb7aa52 137 q15_t in; /* Temporary variable */
emilmont 1:fdd22bb7aa52 138 /* Loop over blockSize number of values */
emilmont 1:fdd22bb7aa52 139 blkCnt = blockSize;
emilmont 1:fdd22bb7aa52 140
emilmont 1:fdd22bb7aa52 141 while(blkCnt > 0u)
emilmont 1:fdd22bb7aa52 142 {
emilmont 1:fdd22bb7aa52 143 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 144 /* Compute Sum of squares of the input samples
emilmont 1:fdd22bb7aa52 145 * and then store the result in a temporary variable, sumOfSquares. */
emilmont 1:fdd22bb7aa52 146 in = *pSrc++;
emilmont 1:fdd22bb7aa52 147 sumOfSquares += (in * in);
emilmont 1:fdd22bb7aa52 148
emilmont 1:fdd22bb7aa52 149 /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
emilmont 1:fdd22bb7aa52 150 /* Compute sum of all input values and then store the result in a temporary variable, sum. */
emilmont 1:fdd22bb7aa52 151 sum += in;
emilmont 1:fdd22bb7aa52 152
emilmont 1:fdd22bb7aa52 153 /* Decrement the loop counter */
emilmont 1:fdd22bb7aa52 154 blkCnt--;
emilmont 1:fdd22bb7aa52 155 }
emilmont 1:fdd22bb7aa52 156
emilmont 1:fdd22bb7aa52 157 /* Compute Mean of squares of the input samples
emilmont 1:fdd22bb7aa52 158 * and then store the result in a temporary variable, meanOfSquares. */
emilmont 1:fdd22bb7aa52 159 t = (q15_t) ((1.0f / (float32_t) (blockSize - 1u)) * 16384);
emilmont 1:fdd22bb7aa52 160 sumOfSquares = __SSAT((sumOfSquares >> 15u), 16u);
emilmont 1:fdd22bb7aa52 161 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 14u);
emilmont 1:fdd22bb7aa52 162
emilmont 1:fdd22bb7aa52 163 #endif /* #ifndef ARM_MATH_CM0 */
emilmont 1:fdd22bb7aa52 164
emilmont 1:fdd22bb7aa52 165 /* Compute mean of all input values */
emilmont 1:fdd22bb7aa52 166 t = (q15_t) ((1.0f / (float32_t) (blockSize * (blockSize - 1u))) * 32768);
emilmont 1:fdd22bb7aa52 167 mean = __SSAT(sum, 16u);
emilmont 1:fdd22bb7aa52 168
emilmont 1:fdd22bb7aa52 169 /* Compute square of mean */
emilmont 1:fdd22bb7aa52 170 squareOfMean = ((q31_t) mean * mean) >> 15;
emilmont 1:fdd22bb7aa52 171 squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 15);
emilmont 1:fdd22bb7aa52 172
emilmont 1:fdd22bb7aa52 173 /* Compute variance and then store the result to the destination */
emilmont 1:fdd22bb7aa52 174 *pResult = (meanOfSquares - squareOfMean);
emilmont 1:fdd22bb7aa52 175
emilmont 1:fdd22bb7aa52 176 }
emilmont 1:fdd22bb7aa52 177
emilmont 1:fdd22bb7aa52 178 /**
emilmont 1:fdd22bb7aa52 179 * @} end of variance group
emilmont 1:fdd22bb7aa52 180 */