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+/* ----------------------------------------------------------------------
+* Copyright (C) 2010 ARM Limited. All rights reserved.
+*
+* $Date: 15. February 2012
+* $Revision: V1.1.0
+*
+* Project: CMSIS DSP Library
+* Title: arm_rms_q31.c
+*
+* Description: Root Mean Square of the elements of a Q31 vector.
+*
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*
+* Version 1.1.0 2012/02/15
+* Updated with more optimizations, bug fixes and minor API changes.
+*
+* Version 1.0.10 2011/7/15
+* Big Endian support added and Merged M0 and M3/M4 Source code.
+*
+* 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)
+{
+ q63_t sum = 0; /* accumulator */
+ q31_t in; /* Temporary variable to store the input */
+ uint32_t blkCnt; /* loop counter */
+
+#ifndef ARM_MATH_CM0
+
+ /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+ q31_t in1, in2, in3, in4; /* Temporary input variables */
+
+ /*loop Unrolling */
+ blkCnt = blockSize >> 2u;
+
+ /* First part of the processing with loop unrolling. Compute 8 outputs at a time.
+ ** a second loop below computes the remaining 1 to 7 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 */
+ /* read two samples from source buffer */
+ in1 = pSrc[0];
+ in2 = pSrc[1];
+
+ /* calculate power and accumulate to accumulator */
+ sum += (q63_t) in1 *in1;
+ sum += (q63_t) in2 *in2;
+
+ /* read two samples from source buffer */
+ in3 = pSrc[2];
+ in4 = pSrc[3];
+
+ /* calculate power and accumulate to accumulator */
+ sum += (q63_t) in3 *in3;
+ sum += (q63_t) in4 *in4;
+
+
+ /* update source buffer to process next samples */
+ pSrc += 4u;
+
+ /* Decrement the loop counter */
+ blkCnt--;
+ }
+
+ /* If the blockSize is not a multiple of 8, compute any remaining output samples here.
+ ** No loop unrolling is used. */
+ blkCnt = blockSize % 0x4u;
+
+#else
+
+ /* Run the below code for Cortex-M0 */
+ blkCnt = blockSize;
+
+#endif /* #ifndef ARM_MATH_CM0 */
+
+ 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 = *pSrc++;
+ sum += (q63_t) in *in;
+
+ /* Decrement the loop counter */
+ blkCnt--;
+ }
+
+ /* Convert data in 2.62 to 1.31 by 31 right shifts and saturate */
+
+ sum = __SSAT(sum >> 31, 31);
+
+
+ /* Compute Rms and store the result in the destination vector */
+ arm_sqrt_q31((q31_t) ((q31_t) sum / (int32_t) blockSize), pResult);
+}
+
+/**
+ * @} end of RMS group
+ */