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CMSIS/DSP/Source/SupportFunctions/arm_q31_to_q15.c

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+/* ----------------------------------------------------------------------
+ * Project:      CMSIS DSP Library
+ * Title:        arm_q31_to_q15.c
+ * Description:  Converts the elements of the Q31 vector to Q15 vector
+ *
+ * $Date:        23 April 2021
+ * $Revision:    V1.9.0
+ *
+ * Target Processor: Cortex-M and Cortex-A cores
+ * -------------------------------------------------------------------- */
+/*
+ * Copyright (C) 2010-2021 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 "dsp/support_functions.h"
+
+/**
+  @ingroup groupSupport
+ */
+
+/**
+  @addtogroup q31_to_x
+  @{
+ */
+
+/**
+  @brief         Converts the elements of the Q31 vector to Q15 vector.
+  @param[in]     pSrc       points to the Q31 input vector
+  @param[out]    pDst       points to the Q15 output vector
+  @param[in]     blockSize  number of samples in each vector
+  @return        none
+
+  @par           Details
+                   The equation used for the conversion process is:
+  <pre>
+      pDst[n] = (q15_t) pSrc[n] >> 16;   0 <= n < blockSize.
+  </pre>
+ */
+#if defined(ARM_MATH_MVEI) && !defined(ARM_MATH_AUTOVECTORIZE)
+void arm_q31_to_q15(
+  const q31_t * pSrc,
+        q15_t * pDst,
+        uint32_t blockSize)
+{
+    uint32_t  blkCnt;           /* loop counters */
+    q31x4x2_t tmp;
+    q15x8_t vecDst = { 0 };
+    q31_t const *pSrcVec;
+
+
+    pSrcVec = (q31_t const *) pSrc;
+    blkCnt = blockSize >> 3;
+    while (blkCnt > 0U)
+    {
+        /* C = (q15_t) A >> 16 */
+        /* convert from q31 to q15 and then store the results in the destination buffer */
+        tmp = vld2q(pSrcVec);   
+        pSrcVec += 8;
+        vecDst = vshrnbq_n_s32(vecDst, tmp.val[0], 16);
+        vecDst = vshrntq_n_s32(vecDst, tmp.val[1], 16);
+        vst1q(pDst, vecDst);    
+        pDst += 8;
+        /*
+         * Decrement the blockSize loop counter
+         */
+        blkCnt--;
+    }
+
+    /*
+     * tail
+     */
+    blkCnt = blockSize & 7;
+    while (blkCnt > 0U)
+    {
+      /* C = (q15_t) (A >> 16) */
+  
+      /* Convert from q31 to q15 and store result in destination buffer */
+      *pDst++ = (q15_t) (*pSrcVec++ >> 16);
+  
+      /* Decrement loop counter */
+      blkCnt--;
+    }
+}
+
+#else
+void arm_q31_to_q15(
+  const q31_t * pSrc,
+        q15_t * pDst,
+        uint32_t blockSize)
+{
+        uint32_t blkCnt;                               /* Loop counter */
+  const q31_t *pIn = pSrc;                             /* Source pointer */
+
+#if defined (ARM_MATH_LOOPUNROLL) && defined (ARM_MATH_DSP)
+        q31_t in1, in2, in3, in4;
+        q31_t out1, out2;
+#endif
+
+#if defined (ARM_MATH_LOOPUNROLL)
+
+  /* Loop unrolling: Compute 4 outputs at a time */
+  blkCnt = blockSize >> 2U;
+
+  while (blkCnt > 0U)
+  {
+    /* C = (q15_t) (A >> 16) */
+
+    /* Convert from q31 to q15 and store result in destination buffer */
+#if defined (ARM_MATH_DSP)
+
+    in1 = *pIn++;
+    in2 = *pIn++;
+    in3 = *pIn++;
+    in4 = *pIn++;
+
+    /* pack two higher 16-bit values from two 32-bit values */
+#ifndef ARM_MATH_BIG_ENDIAN
+    out1 = __PKHTB(in2, in1, 16);
+    out2 = __PKHTB(in4, in3, 16);
+#else
+    out1 = __PKHTB(in1, in2, 16);
+    out2 = __PKHTB(in3, in4, 16);
+#endif /* #ifdef ARM_MATH_BIG_ENDIAN */
+
+    write_q15x2_ia (&pDst, out1);
+    write_q15x2_ia (&pDst, out2);
+
+#else
+
+    *pDst++ = (q15_t) (*pIn++ >> 16);
+    *pDst++ = (q15_t) (*pIn++ >> 16);
+    *pDst++ = (q15_t) (*pIn++ >> 16);
+    *pDst++ = (q15_t) (*pIn++ >> 16);
+
+#endif /* #if defined (ARM_MATH_DSP) */
+
+    /* Decrement loop counter */
+    blkCnt--;
+  }
+
+  /* Loop unrolling: Compute remaining outputs */
+  blkCnt = blockSize % 0x4U;
+
+#else
+
+  /* Initialize blkCnt with number of samples */
+  blkCnt = blockSize;
+
+#endif /* #if defined (ARM_MATH_LOOPUNROLL) */
+
+  while (blkCnt > 0U)
+  {
+    /* C = (q15_t) (A >> 16) */
+
+    /* Convert from q31 to q15 and store result in destination buffer */
+    *pDst++ = (q15_t) (*pIn++ >> 16);
+
+    /* Decrement loop counter */
+    blkCnt--;
+  }
+
+}
+#endif /* defined(ARM_MATH_MVEI) */
+
+/**
+  @} end of q31_to_x group
+ */