CMSIS DSP library
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arm_var_q31.c
00001 /* ---------------------------------------------------------------------- 00002 * Copyright (C) 2010-2013 ARM Limited. All rights reserved. 00003 * 00004 * $Date: 17. January 2013 00005 * $Revision: V1.4.1 00006 * 00007 * Project: CMSIS DSP Library 00008 * Title: arm_var_q31.c 00009 * 00010 * Description: Variance of an array of Q31 type. 00011 * 00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 00013 * 00014 * Redistribution and use in source and binary forms, with or without 00015 * modification, are permitted provided that the following conditions 00016 * are met: 00017 * - Redistributions of source code must retain the above copyright 00018 * notice, this list of conditions and the following disclaimer. 00019 * - Redistributions in binary form must reproduce the above copyright 00020 * notice, this list of conditions and the following disclaimer in 00021 * the documentation and/or other materials provided with the 00022 * distribution. 00023 * - Neither the name of ARM LIMITED nor the names of its contributors 00024 * may be used to endorse or promote products derived from this 00025 * software without specific prior written permission. 00026 * 00027 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 00028 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 00029 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 00030 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 00031 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 00032 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 00033 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 00034 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 00035 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 00036 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 00037 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 00038 * POSSIBILITY OF SUCH DAMAGE. 00039 * -------------------------------------------------------------------- */ 00040 00041 #include "arm_math.h" 00042 00043 /** 00044 * @ingroup groupStats 00045 */ 00046 00047 /** 00048 * @addtogroup variance 00049 * @{ 00050 */ 00051 00052 /** 00053 * @brief Variance of the elements of a Q31 vector. 00054 * @param[in] *pSrc points to the input vector 00055 * @param[in] blockSize length of the input vector 00056 * @param[out] *pResult variance value returned here 00057 * @return none. 00058 * 00059 * @details 00060 * <b>Scaling and Overflow Behavior:</b> 00061 * 00062 *\par 00063 * The function is implemented using an internal 64-bit accumulator. 00064 * The input is represented in 1.31 format, and intermediate multiplication 00065 * yields a 2.62 format. 00066 * The accumulator maintains full precision of the intermediate multiplication results, 00067 * but provides only a single guard bit. 00068 * There is no saturation on intermediate additions. 00069 * If the accumulator overflows it wraps around and distorts the result. 00070 * In order to avoid overflows completely the input signal must be scaled down by 00071 * log2(blockSize) bits, as a total of blockSize additions are performed internally. 00072 * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value. 00073 * 00074 */ 00075 00076 00077 void arm_var_q31( 00078 q31_t * pSrc, 00079 uint32_t blockSize, 00080 q63_t * pResult) 00081 { 00082 q63_t sum = 0, sumSquare = 0; /* Accumulator */ 00083 q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ 00084 q31_t mean; /* mean */ 00085 q31_t in; /* input value */ 00086 q31_t t; /* Temporary variable */ 00087 uint32_t blkCnt; /* loop counter */ 00088 00089 #ifndef ARM_MATH_CM0_FAMILY 00090 00091 /* Run the below code for Cortex-M4 and Cortex-M3 */ 00092 q63_t sumSquare1 = 0; /* Accumulator */ 00093 q31_t in1, in2, in3, in4; /* Temporary input variables */ 00094 00095 /*loop Unrolling */ 00096 blkCnt = blockSize >> 2u; 00097 00098 /* First part of the processing with loop unrolling. Compute 4 outputs at a time. 00099 ** a second loop below computes the remaining 1 to 3 samples. */ 00100 while(blkCnt > 0u) 00101 { 00102 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00103 /* Compute Sum of squares of the input samples 00104 * and then store the result in a temporary variable, sum. */ 00105 /* read input samples from source buffer */ 00106 in1 = pSrc[0]; 00107 in2 = pSrc[1]; 00108 00109 /* calculate sum of inputs */ 00110 sum += in1; 00111 /* calculate sum of squares */ 00112 sumSquare += ((q63_t) (in1) * (in1)); 00113 in3 = pSrc[2]; 00114 sum += in2; 00115 sumSquare1 += ((q63_t) (in2) * (in2)); 00116 in4 = pSrc[3]; 00117 sum += in3; 00118 sumSquare += ((q63_t) (in3) * (in3)); 00119 sum += in4; 00120 sumSquare1 += ((q63_t) (in4) * (in4)); 00121 00122 /* update input pointer to process next samples */ 00123 pSrc += 4u; 00124 00125 /* Decrement the loop counter */ 00126 blkCnt--; 00127 } 00128 00129 /* add two accumulators */ 00130 sumSquare = sumSquare + sumSquare1; 00131 00132 /* If the blockSize is not a multiple of 4, compute any remaining output samples here. 00133 ** No loop unrolling is used. */ 00134 blkCnt = blockSize % 0x4u; 00135 00136 #else 00137 00138 /* Run the below code for Cortex-M0 */ 00139 blkCnt = blockSize; 00140 00141 #endif /* #ifndef ARM_MATH_CM0_FAMILY */ 00142 00143 while(blkCnt > 0u) 00144 { 00145 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00146 /* Compute Sum of squares of the input samples 00147 * and then store the result in a temporary variable, sum. */ 00148 in = *pSrc++; 00149 sumSquare += ((q63_t) (in) * (in)); 00150 sum += in; 00151 00152 /* Decrement the loop counter */ 00153 blkCnt--; 00154 } 00155 00156 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); 00157 00158 /* Compute Mean of squares of the input samples 00159 * and then store the result in a temporary variable, meanOfSquares. */ 00160 sumSquare = (sumSquare >> 31); 00161 meanOfSquares = (q31_t) ((sumSquare * t) >> 30); 00162 00163 /* Compute mean of all input values */ 00164 t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f); 00165 mean = (q31_t) (sum); 00166 00167 /* Compute square of mean */ 00168 squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31); 00169 squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31); 00170 00171 /* Compute variance and then store the result to the destination */ 00172 *pResult = (q63_t) meanOfSquares - squareOfMean; 00173 00174 } 00175 00176 /** 00177 * @} end of variance group 00178 */
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