Diff: cmsis_dsp/StatisticsFunctions/arm_var_q31.c

Revision:

5:3762170b6d4d

Parent:

3:7a284390b0ce

--- a/cmsis_dsp/StatisticsFunctions/arm_var_q31.c	Mon Jun 23 09:30:09 2014 +0100
+++ b/cmsis_dsp/StatisticsFunctions/arm_var_q31.c	Fri Nov 20 08:45:18 2015 +0000
@@ -1,8 +1,8 @@
 /* ----------------------------------------------------------------------    
-* Copyright (C) 2010-2013 ARM Limited. All rights reserved.    
+* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
 *    
-* $Date:        17. January 2013
-* $Revision: 	V1.4.1  
+* $Date:        19. March 2015
+* $Revision: 	V.1.4.5  
 *    
 * Project: 	    CMSIS DSP Library    
 * Title:		arm_var_q31.c    
@@ -61,15 +61,16 @@
  *        
  *\par        
  * The function is implemented using an internal 64-bit accumulator.        
- * The input is represented in 1.31 format, and intermediate multiplication        
- * yields a 2.62 format.        
+ * The input is represented in 1.31 format, which is then downshifted by 8 bits
+ * which yields 1.23, and intermediate multiplication yields a 2.46 format.        
  * The accumulator maintains full precision of the intermediate multiplication results,         
- * but provides only a single guard bit.        
+ * but provides only a 16 guard bits.        
  * There is no saturation on intermediate additions.        
  * If the accumulator overflows it wraps around and distorts the result.        
  * In order to avoid overflows completely the input signal must be scaled down by         
- * log2(blockSize) bits, as a total of blockSize additions are performed internally.         
- * Finally, the 2.62 accumulator is right shifted by 31 bits to yield a 1.31 format value.        
+ * log2(blockSize)-8 bits, as a total of blockSize additions are performed internally.  
+ * After division, internal variables should be Q18.46 
+ * Finally, the 18.46 accumulator is right shifted by 15 bits to yield a 1.31 format value.        
  *        
  */
 
@@ -77,20 +78,23 @@
 void arm_var_q31(
   q31_t * pSrc,
   uint32_t blockSize,
-  q63_t * pResult)
+  q31_t * pResult)
 {
-  q63_t sum = 0, sumSquare = 0;                  /* Accumulator */
-  q31_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
-  q31_t mean;                                    /* mean */
+  q63_t sum = 0;                                 /* Accumulator */
+  q63_t meanOfSquares, squareOfMean;             /* square of mean and mean of square */
   q31_t in;                                      /* input value */
-  q31_t t;                                       /* Temporary variable */
   uint32_t blkCnt;                               /* loop counter */
+  q63_t sumOfSquares = 0;                        /* Accumulator */
 
+	if(blockSize == 1)
+	{
+		*pResult = 0;
+		return;
+	}
+   
 #ifndef ARM_MATH_CM0_FAMILY
 
   /* Run the below code for Cortex-M4 and Cortex-M3 */
-  q63_t sumSquare1 = 0;                          /* Accumulator */
-  q31_t in1, in2, in3, in4;                      /* Temporary input variables */
 
   /*loop Unrolling */
   blkCnt = blockSize >> 2u;
@@ -100,76 +104,81 @@
   while(blkCnt > 0u)
   {
     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1])  */
-    /* Compute Sum of squares of the input samples        
+    /* Compute Sum of squares of the input samples    
      * and then store the result in a temporary variable, sum. */
-    /* read input samples from source buffer */
-    in1 = pSrc[0];
-    in2 = pSrc[1];
-
-    /* calculate sum of inputs */
-    sum += in1;
-    /* calculate sum of squares */
-    sumSquare += ((q63_t) (in1) * (in1));
-    in3 = pSrc[2];
-    sum += in2;
-    sumSquare1 += ((q63_t) (in2) * (in2));
-    in4 = pSrc[3];
-    sum += in3;
-    sumSquare += ((q63_t) (in3) * (in3));
-    sum += in4;
-    sumSquare1 += ((q63_t) (in4) * (in4));
-
-    /* update input pointer to process next samples */
-    pSrc += 4u;
+    in = *pSrc++ >> 8;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++ >> 8;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++ >> 8;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+    in = *pSrc++ >> 8;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
 
     /* Decrement the loop counter */
     blkCnt--;
   }
 
-  /* add two accumulators */
-  sumSquare = sumSquare + sumSquare1;
-
   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
    ** No loop unrolling is used. */
   blkCnt = blockSize % 0x4u;
 
+  while(blkCnt > 0u)
+  {
+    /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
+    /* Compute Sum of squares of the input samples    
+     * and then store the result in a temporary variable, sum. */
+    in = *pSrc++ >> 8;
+    sum += in;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* Decrement the loop counter */
+    blkCnt--;
+  }
+
+  /* Compute Mean of squares of the input samples    
+   * and then store the result in a temporary variable, meanOfSquares. */
+  meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1);
+
 #else
 
   /* Run the below code for Cortex-M0 */
+
+  /* Loop over blockSize number of values */
   blkCnt = blockSize;
 
-#endif /* #ifndef ARM_MATH_CM0_FAMILY */
-
   while(blkCnt > 0u)
   {
     /* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
-    /* Compute Sum of squares of the input samples        
-     * and then store the result in a temporary variable, sum. */
-    in = *pSrc++;
-    sumSquare += ((q63_t) (in) * (in));
+    /* Compute Sum of squares of the input samples     
+     * and then store the result in a temporary variable, sumOfSquares. */
+    in = *pSrc++ >> 8;
+    sumOfSquares += ((q63_t) (in) * (in));
+
+    /* C = (A[0] + A[1] + A[2] + ... + A[blockSize-1]) */
+    /* Compute sum of all input values and then store the result in a temporary variable, sum. */
     sum += in;
 
     /* Decrement the loop counter */
     blkCnt--;
   }
 
-  t = (q31_t) ((1.0f / (float32_t) (blockSize - 1u)) * 1073741824.0f);
-
-  /* Compute Mean of squares of the input samples        
+  /* Compute Mean of squares of the input samples     
    * and then store the result in a temporary variable, meanOfSquares. */
-  sumSquare = (sumSquare >> 31);
-  meanOfSquares = (q31_t) ((sumSquare * t) >> 30);
+  meanOfSquares = sumOfSquares / (q63_t)(blockSize - 1);
 
-  /* Compute mean of all input values */
-  t = (q31_t) ((1.0f / (blockSize * (blockSize - 1u))) * 2147483648.0f);
-  mean = (q31_t) (sum);
+#endif /* #ifndef ARM_MATH_CM0_FAMILY */
 
   /* Compute square of mean */
-  squareOfMean = (q31_t) (((q63_t) mean * mean) >> 31);
-  squareOfMean = (q31_t) (((q63_t) squareOfMean * t) >> 31);
+  squareOfMean = sum * sum / (q63_t)(blockSize * (blockSize - 1u));
+
 
-  /* Compute variance and then store the result to the destination */
-  *pResult = (q63_t) meanOfSquares - squareOfMean;
+  /* Compute standard deviation and then store the result to the destination */
+  *pResult = (meanOfSquares - squareOfMean) >> 15;
 
 }