CMSIS DSP library
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arm_std_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_std_q31.c 00009 * 00010 * Description: Standard deviation 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 STD 00049 * @{ 00050 */ 00051 00052 00053 /** 00054 * @brief Standard deviation of the elements of a Q31 vector. 00055 * @param[in] *pSrc points to the input vector 00056 * @param[in] blockSize length of the input vector 00057 * @param[out] *pResult standard deviation value returned here 00058 * @return none. 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_std_q31( 00078 q31_t * pSrc, 00079 uint32_t blockSize, 00080 q31_t * pResult) 00081 { 00082 q63_t sum = 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 q63_t sumOfSquares = 0; /* Accumulator */ 00089 00090 #ifndef ARM_MATH_CM0_FAMILY 00091 00092 /* Run the below code for Cortex-M4 and Cortex-M3 */ 00093 00094 /*loop Unrolling */ 00095 blkCnt = blockSize >> 2u; 00096 00097 /* First part of the processing with loop unrolling. Compute 4 outputs at a time. 00098 ** a second loop below computes the remaining 1 to 3 samples. */ 00099 while(blkCnt > 0u) 00100 { 00101 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00102 /* Compute Sum of squares of the input samples 00103 * and then store the result in a temporary variable, sum. */ 00104 in = *pSrc++; 00105 sum += in; 00106 sumOfSquares += ((q63_t) (in) * (in)); 00107 in = *pSrc++; 00108 sum += in; 00109 sumOfSquares += ((q63_t) (in) * (in)); 00110 in = *pSrc++; 00111 sum += in; 00112 sumOfSquares += ((q63_t) (in) * (in)); 00113 in = *pSrc++; 00114 sum += in; 00115 sumOfSquares += ((q63_t) (in) * (in)); 00116 00117 /* Decrement the loop counter */ 00118 blkCnt--; 00119 } 00120 00121 /* If the blockSize is not a multiple of 4, compute any remaining output samples here. 00122 ** No loop unrolling is used. */ 00123 blkCnt = blockSize % 0x4u; 00124 00125 while(blkCnt > 0u) 00126 { 00127 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00128 /* Compute Sum of squares of the input samples 00129 * and then store the result in a temporary variable, sum. */ 00130 in = *pSrc++; 00131 sum += in; 00132 sumOfSquares += ((q63_t) (in) * (in)); 00133 00134 /* Decrement the loop counter */ 00135 blkCnt--; 00136 } 00137 00138 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); 00139 00140 /* Compute Mean of squares of the input samples 00141 * and then store the result in a temporary variable, meanOfSquares. */ 00142 sumOfSquares = (sumOfSquares >> 31); 00143 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30); 00144 00145 #else 00146 00147 /* Run the below code for Cortex-M0 */ 00148 00149 /* Loop over blockSize number of values */ 00150 blkCnt = blockSize; 00151 00152 while(blkCnt > 0u) 00153 { 00154 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00155 /* Compute Sum of squares of the input samples 00156 * and then store the result in a temporary variable, sumOfSquares. */ 00157 in = *pSrc++; 00158 sumOfSquares += ((q63_t) (in) * (in)); 00159 00160 /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */ 00161 /* Compute sum of all input values and then store the result in a temporary variable, sum. */ 00162 sum += in; 00163 00164 /* Decrement the loop counter */ 00165 blkCnt--; 00166 } 00167 00168 /* Compute Mean of squares of the input samples 00169 * and then store the result in a temporary variable, meanOfSquares. */ 00170 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); 00171 sumOfSquares = (sumOfSquares >> 31); 00172 meanOfSquares = (q31_t) ((sumOfSquares * t) >> 30); 00173 00174 #endif /* #ifndef ARM_MATH_CM0_FAMILY */ 00175 00176 /* Compute mean of all input values */ 00177 t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f); 00178 mean = (q31_t) (sum); 00179 00180 /* Compute square of mean */ 00181 squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31); 00182 squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31); 00183 00184 00185 /* Compute standard deviation and then store the result to the destination */ 00186 arm_sqrt_q31(meanOfSquares - squareOfMean, pResult); 00187 00188 } 00189 00190 /** 00191 * @} end of STD group 00192 */
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