arm_var_q31.c
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00001 /* ---------------------------------------------------------------------- 00002 * Copyright (C) 2011 ARM Limited. All rights reserved. 00003 * 00004 * $Date: 15. December 2011 00005 * $Revision: V2.0.0 00006 * 00007 * Project: Cortex-R DSP Library 00008 * Title: arm_var_q31.c 00009 * 00010 * Description: Variance of an array of Q31 type. 00011 * 00012 * Target Processor: Cortex-R4/R5 00013 * 00014 * Version 1.0.0 2011/03/08 00015 * Alpha release. 00016 * 00017 * Version 1.0.1 2011/09/30 00018 * Beta release. 00019 * 00020 * Version 2.0.0 2011/12/15 00021 * Final release. 00022 * 00023 * -------------------------------------------------------------------- */ 00024 #include "arm_math.h" 00025 00060 void arm_var_q31( 00061 q31_t * pSrc, 00062 uint32_t blockSize, 00063 q63_t * pResult) 00064 { 00065 q63_t sum = 0, sumSquare = 0, sumSquare1 = 0; /* Accumulator */ 00066 q31_t meanOfSquares, squareOfMean; /* square of mean and mean of square */ 00067 q31_t mean; /* mean */ 00068 q31_t in; /* input value */ 00069 q31_t t; /* Temporary variable */ 00070 uint32_t blkCnt; /* loop counter */ 00071 q31_t in1, in2, in3, in4; /* Temporary input variables */ 00072 00073 /*loop Unrolling */ 00074 blkCnt = blockSize >> 3u; 00075 00076 /* First part of the processing with loop unrolling. Compute 8 outputs at a time. 00077 ** a second loop below computes the remaining 1 to 7 samples. */ 00078 while(blkCnt > 0u) 00079 { 00080 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00081 /* Compute Sum of squares of the input samples 00082 * and then store the result in a temporary variable, sum. */ 00083 /* read input samples from source buffer */ 00084 in1 = pSrc[0]; 00085 in2 = pSrc[1]; 00086 00087 /* calculate sum of inputs */ 00088 sum += in1; 00089 /* calculate sum of squares */ 00090 sumSquare += ((q63_t) (in1) * (in1)); 00091 in3 = pSrc[2]; 00092 sum += in2; 00093 sumSquare1 += ((q63_t) (in2) * (in2)); 00094 in4 = pSrc[3]; 00095 sum += in3; 00096 sumSquare += ((q63_t) (in3) * (in3)); 00097 in1 = pSrc[4]; 00098 sum += in4; 00099 sumSquare1 += ((q63_t) (in4) * (in4)); 00100 in2 = pSrc[5]; 00101 sum += in1; 00102 sumSquare += ((q63_t) (in1) * (in1)); 00103 in3 = pSrc[6]; 00104 sum += in2; 00105 sumSquare1 += ((q63_t) (in2) * (in2)); 00106 in4 = pSrc[7]; 00107 sum += in3; 00108 sumSquare += ((q63_t) (in3) * (in3)); 00109 sum += in4; 00110 sumSquare1 += ((q63_t) (in4) * (in4)); 00111 00112 /* update input pointer to process next samples */ 00113 pSrc += 8u; 00114 00115 /* Decrement the loop counter */ 00116 blkCnt--; 00117 } 00118 00119 /* add two accumulators */ 00120 sumSquare = sumSquare + sumSquare1; 00121 00122 /* If the blockSize is not a multiple of 8, compute any remaining output samples here. 00123 ** No loop unrolling is used. */ 00124 blkCnt = blockSize % 0x8u; 00125 00126 while(blkCnt > 0u) 00127 { 00128 /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */ 00129 /* Compute Sum of squares of the input samples 00130 * and then store the result in a temporary variable, sum. */ 00131 in = *pSrc++; 00132 sumSquare += ((q63_t) (in) * (in)); 00133 sum += in; 00134 00135 /* Decrement the loop counter */ 00136 blkCnt--; 00137 } 00138 00139 t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f); 00140 00141 /* Compute Mean of squares of the input samples 00142 * and then store the result in a temporary variable, meanOfSquares. */ 00143 sumSquare = (sumSquare >> 31); 00144 meanOfSquares = (q31_t) ((sumSquare * t) >> 30); 00145 00146 /* Compute mean of all input values */ 00147 t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f); 00148 mean = (q31_t) (sum); 00149 00150 /* Compute square of mean */ 00151 squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31); 00152 squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31); 00153 00154 /* Compute variance and then store the result to the destination */ 00155 *pResult = (q63_t) meanOfSquares - squareOfMean; 00156 00157 } 00158
