arm_var_f32.c

00001 /* ----------------------------------------------------------------------    
00002 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
00003 *    
00004 * $Date:        12. March 2014
00005 * $Revision:    V1.4.3  
00006 *    
00007 * Project:      CMSIS DSP Library    
00008 * Title:        arm_var_f32.c    
00009 *    
00010 * Description:  Variance of the elements of a floating-point vector.    
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  * @defgroup variance  Variance    
00049  *    
00050  * Calculates the variance of the elements in the input vector.    
00051  * The underlying algorithm is used:    
00052  *    
00053  * <pre>    
00054  *  Result = (sumOfSquares - sum<sup>2</sup> / blockSize) / (blockSize - 1)   
00055  *   
00056  *     where, sumOfSquares = pSrc[0] * pSrc[0] + pSrc[1] * pSrc[1] + ... + pSrc[blockSize-1] * pSrc[blockSize-1]   
00057  *   
00058  *                     sum = pSrc[0] + pSrc[1] + pSrc[2] + ... + pSrc[blockSize-1]   
00059  * </pre>   
00060  *    
00061  * There are separate functions for floating point, Q31, and Q15 data types.    
00062  */
00063 
00064 /**    
00065  * @addtogroup variance    
00066  * @{    
00067  */
00068 
00069 
00070 /**    
00071  * @brief Variance of the elements of a floating-point vector.    
00072  * @param[in]       *pSrc points to the input vector    
00073  * @param[in]       blockSize length of the input vector    
00074  * @param[out]      *pResult variance value returned here    
00075  * @return none.    
00076  *    
00077  */
00078 
00079 
00080 void arm_var_f32(
00081   float32_t * pSrc,
00082   uint32_t blockSize,
00083   float32_t * pResult)
00084 {
00085 
00086   float32_t sum = 0.0f;                          /* Temporary result storage */
00087   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
00088   float32_t in;                                  /* input value */
00089   uint32_t blkCnt;                               /* loop counter */
00090   
00091 #ifndef ARM_MATH_CM0_FAMILY
00092    
00093   /* Run the below code for Cortex-M4 and Cortex-M3 */
00094 
00095   float32_t meanOfSquares, mean, squareOfMean;   /* Temporary variables */
00096 
00097     if(blockSize == 1)
00098     {
00099         *pResult = 0;
00100         return;
00101     }
00102 
00103   /*loop Unrolling */
00104   blkCnt = blockSize >> 2u;
00105 
00106   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
00107    ** a second loop below computes the remaining 1 to 3 samples. */
00108   while(blkCnt > 0u)
00109   {
00110     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
00111     /* Compute Sum of squares of the input samples    
00112      * and then store the result in a temporary variable, sum. */
00113     in = *pSrc++;
00114     sum += in;
00115     sumOfSquares += in * in;
00116     in = *pSrc++;
00117     sum += in;
00118     sumOfSquares += in * in;
00119     in = *pSrc++;
00120     sum += in;
00121     sumOfSquares += in * in;
00122     in = *pSrc++;
00123     sum += in;
00124     sumOfSquares += in * in;
00125 
00126     /* Decrement the loop counter */
00127     blkCnt--;
00128   }
00129 
00130   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
00131    ** No loop unrolling is used. */
00132   blkCnt = blockSize % 0x4u;
00133 
00134   while(blkCnt > 0u)
00135   {
00136     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
00137     /* Compute Sum of squares of the input samples    
00138      * and then store the result in a temporary variable, sum. */
00139     in = *pSrc++;
00140     sum += in;
00141     sumOfSquares += in * in;
00142 
00143     /* Decrement the loop counter */
00144     blkCnt--;
00145   }
00146 
00147   /* Compute Mean of squares of the input samples    
00148    * and then store the result in a temporary variable, meanOfSquares. */
00149   meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
00150 
00151   /* Compute mean of all input values */
00152   mean = sum / (float32_t) blockSize;
00153 
00154   /* Compute square of mean */
00155   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
00156                                   ((float32_t) blockSize - 1.0f));
00157 
00158   /* Compute variance and then store the result to the destination */
00159   *pResult = meanOfSquares - squareOfMean;
00160 
00161 #else
00162 
00163   /* Run the below code for Cortex-M0 */
00164   float32_t squareOfSum;                         /* Square of Sum */
00165 
00166     if(blockSize == 1)
00167     {
00168         *pResult = 0;
00169         return;
00170     }
00171 
00172   /* Loop over blockSize number of values */
00173   blkCnt = blockSize;
00174 
00175   while(blkCnt > 0u)
00176   {
00177     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
00178     /* Compute Sum of squares of the input samples     
00179      * and then store the result in a temporary variable, sumOfSquares. */
00180     in = *pSrc++;
00181     sumOfSquares += in * in;
00182 
00183     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
00184     /* Compute Sum of the input samples     
00185      * and then store the result in a temporary variable, sum. */
00186     sum += in;
00187 
00188     /* Decrement the loop counter */
00189     blkCnt--;
00190   }
00191 
00192   /* Compute the square of sum */
00193   squareOfSum = ((sum * sum) / (float32_t) blockSize);
00194 
00195   /* Compute the variance */
00196   *pResult = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
00197 
00198 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
00199 
00200 }
00201 
00202 /**    
00203  * @} end of variance group    
00204  */