Diff: src/Cortex-M4-M3/StatisticsFunctions/arm_rms_q31.c

Revision:

0:1014af42efd9

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Cortex-M4-M3/StatisticsFunctions/arm_rms_q31.c	Thu Mar 10 15:07:50 2011 +0000
@@ -0,0 +1,115 @@
+/* ----------------------------------------------------------------------  
+* Copyright (C) 2010 ARM Limited. All rights reserved.  
+*  
+* $Date:        29. November 2010  
+* $Revision: 	V1.0.3  
+*  
+* Project: 	    CMSIS DSP Library  
+* Title:		arm_rms_q31.c  
+*  
+* Description:	root mean square value of an array of Q31 type  
+*  
+* Target Processor: Cortex-M4/Cortex-M3
+*  
+* Version 1.0.3 2010/11/29 
+*    Re-organized the CMSIS folders and updated documentation.  
+*   
+* Version 1.0.2 2010/11/11  
+*    Documentation updated.   
+*  
+* Version 1.0.1 2010/10/05   
+*    Production release and review comments incorporated.  
+*  
+* Version 1.0.0 2010/09/20   
+*    Production release and review comments incorporated.  
+* ---------------------------------------------------------------------------- */ 
+ 
+#include "arm_math.h" 
+ 
+/**  
+ * @addtogroup RMS  
+ * @{  
+ */ 
+ 
+ 
+/**  
+ * @brief Root Mean Square of the elements of a Q31 vector.  
+ * @param[in]       *pSrc points to the input vector  
+ * @param[in]       blockSize length of the input vector  
+ * @param[out]      *pResult rms value returned here  
+ * @return none.  
+ *  
+ * @details  
+ * <b>Scaling and Overflow Behavior:</b>  
+ *  
+ *\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 accumulator maintains full precision of the intermediate multiplication results,   
+ * but provides only a single guard bit.  
+ * 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.  
+ *  
+ */ 
+ 
+void arm_rms_q31( 
+  q31_t * pSrc, 
+  uint32_t blockSize, 
+  q31_t * pResult) 
+{ 
+  q31_t *pIn1 = pSrc;                            /* SrcA pointer */ 
+  q63_t sum = 0;                                 /* accumulator */ 
+  q31_t in;                                      /* Temporary variable to store the input */ 
+  uint32_t blkCnt;                               /* loop counter */ 
+ 
+  /*loop Unrolling */ 
+  blkCnt = blockSize >> 2u; 
+ 
+  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
+   ** a second loop below computes the remaining 1 to 3 samples. */ 
+  while(blkCnt > 0u) 
+  { 
+    /* C = A[0] * A[0] + A[1] * A[1] + A[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */ 
+    /* Compute sum of the squares and then store the result in a temporary variable, sum */ 
+    in = *pIn1++; 
+    sum += (q63_t) in *in; 
+    in = *pIn1++; 
+    sum += (q63_t) in *in; 
+    in = *pIn1++; 
+    sum += (q63_t) in *in; 
+    in = *pIn1++; 
+    sum += (q63_t) in *in; 
+ 
+    /* Decrement the loop counter */ 
+    blkCnt--; 
+  } 
+ 
+  /* 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[2] * A[2] + ... + A[blockSize-1] * A[blockSize-1] */ 
+    /* Compute sum of the squares and then store the results in a temporary variable, sum */ 
+    in = *pIn1++; 
+    sum += (q63_t) in *in; 
+ 
+    /* Decrement the loop counter */ 
+    blkCnt--; 
+  } 
+ 
+  /* Convert data in 2.62 to 1.31 by 31 right shifts */ 
+  sum = sum >> 31; 
+ 
+  /* Compute Rms and store the result in the destination vector */ 
+  arm_sqrt_q31((q31_t) (sum / (int32_t) blockSize), pResult); 
+} 
+ 
+/**  
+ * @} end of RMS group  
+ */