arm_std_f32.c

00001 /* ----------------------------------------------------------------------    
00002 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
00003 *    
00004 * $Date:        19. March 2015
00005 * $Revision:    V.1.4.5  
00006 *    
00007 * Project:      CMSIS DSP Library    
00008 * Title:        arm_std_f32.c    
00009 *    
00010 * Description:  Standard deviation 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 STD Standard deviation    
00049  *    
00050  * Calculates the standard deviation of the elements in the input vector.     
00051  * The underlying algorithm is used:    
00052  *   
00053  * <pre>    
00054  *  Result = sqrt((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 STD    
00066  * @{    
00067  */
00068 
00069 
00070 /**    
00071  * @brief Standard deviation 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 standard deviation value returned here    
00075  * @return none.    
00076  *    
00077  */
00078 
00079 
00080 void arm_std_f32(
00081   float32_t * pSrc,
00082   uint32_t blockSize,
00083   float32_t * pResult)
00084 {
00085   float32_t sum = 0.0f;                          /* Temporary result storage */
00086   float32_t sumOfSquares = 0.0f;                 /* Sum of squares */
00087   float32_t in;                                  /* input value */
00088   uint32_t blkCnt;                               /* loop counter */
00089    
00090 #ifndef ARM_MATH_CM0_FAMILY
00091 
00092   /* Run the below code for Cortex-M4 and Cortex-M3 */
00093 
00094   float32_t meanOfSquares, mean, squareOfMean;
00095 
00096     if(blockSize == 1)
00097     {
00098         *pResult = 0;
00099         return;
00100     }
00101 
00102   /*loop Unrolling */
00103   blkCnt = blockSize >> 2u;
00104 
00105   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
00106    ** a second loop below computes the remaining 1 to 3 samples. */
00107   while(blkCnt > 0u)
00108   {
00109     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
00110     /* Compute Sum of squares of the input samples    
00111      * and then store the result in a temporary variable, sum. */
00112     in = *pSrc++;
00113     sum += in;
00114     sumOfSquares += in * in;
00115     in = *pSrc++;
00116     sum += in;
00117     sumOfSquares += in * in;
00118     in = *pSrc++;
00119     sum += in;
00120     sumOfSquares += in * in;
00121     in = *pSrc++;
00122     sum += in;
00123     sumOfSquares += in * in;
00124 
00125     /* Decrement the loop counter */
00126     blkCnt--;
00127   }
00128 
00129   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
00130    ** No loop unrolling is used. */
00131   blkCnt = blockSize % 0x4u;
00132 
00133   while(blkCnt > 0u)
00134   {
00135     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
00136     /* Compute Sum of squares of the input samples    
00137      * and then store the result in a temporary variable, sum. */
00138     in = *pSrc++;
00139     sum += in;
00140     sumOfSquares += in * in;
00141 
00142     /* Decrement the loop counter */
00143     blkCnt--;
00144   }
00145 
00146   /* Compute Mean of squares of the input samples    
00147    * and then store the result in a temporary variable, meanOfSquares. */
00148   meanOfSquares = sumOfSquares / ((float32_t) blockSize - 1.0f);
00149 
00150   /* Compute mean of all input values */
00151   mean = sum / (float32_t) blockSize;
00152 
00153   /* Compute square of mean */
00154   squareOfMean = (mean * mean) * (((float32_t) blockSize) /
00155                                   ((float32_t) blockSize - 1.0f));
00156 
00157   /* Compute standard deviation and then store the result to the destination */
00158   arm_sqrt_f32((meanOfSquares - squareOfMean), pResult);
00159 
00160 #else
00161 
00162   /* Run the below code for Cortex-M0 */
00163 
00164   float32_t squareOfSum;                         /* Square of Sum */
00165   float32_t var;                                 /* Temporary varaince storage */
00166 
00167     if(blockSize == 1)
00168     {
00169         *pResult = 0;
00170         return;
00171     }
00172 
00173   /* Loop over blockSize number of values */
00174   blkCnt = blockSize;
00175 
00176   while(blkCnt > 0u)
00177   {
00178     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
00179     /* Compute Sum of squares of the input samples     
00180      * and then store the result in a temporary variable, sumOfSquares. */
00181     in = *pSrc++;
00182     sumOfSquares += in * in;
00183 
00184     /* C = (A[0] + A[1] + ... + A[blockSize-1]) */
00185     /* Compute Sum of the input samples     
00186      * and then store the result in a temporary variable, sum. */
00187     sum += in;
00188 
00189     /* Decrement the loop counter */
00190     blkCnt--;
00191   }
00192 
00193   /* Compute the square of sum */
00194   squareOfSum = ((sum * sum) / (float32_t) blockSize);
00195 
00196   /* Compute the variance */
00197   var = ((sumOfSquares - squareOfSum) / (float32_t) (blockSize - 1.0f));
00198 
00199   /* Compute standard deviation and then store the result to the destination */
00200   arm_sqrt_f32(var, pResult);
00201 
00202 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
00203 
00204 }
00205 
00206 /**    
00207  * @} end of STD group    
00208  */