Diff: DSP/source/StatisticsFunctions/arm_rms_q31.c

Revision:

0:eedb7d567a5d

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DSP/source/StatisticsFunctions/arm_rms_q31.c	Thu Apr 12 01:31:58 2018 +0000
@@ -0,0 +1,138 @@
+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_rms_q31.c
+ * Description:  Root Mean Square of the elements of a Q31 vector
+ *
+ * $Date:        27. January 2017
+ * $Revision:    V.1.5.1
+ *
+ * Target Processor: Cortex-M cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the License); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an AS IS BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#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 */
+
+#if defined (ARM_MATH_DSP)
+  /* 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 /* #if defined (ARM_MATH_DSP) */
+
+  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 */
+  /* Compute Rms and store the result in the destination vector */
+  arm_sqrt_q31(clip_q63_to_q31((sum / (q63_t) blockSize) >> 31), pResult);
+}
+
+/**
+ * @} end of RMS group
+ */
+