arm_q31_to_q15.c

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/* ----------------------------------------------------------------------------    
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
*    
* $Date:        19. March 2015
* $Revision:    V.1.4.5  
*    
* Project:      CMSIS DSP Library    
* Title:        arm_q31_to_q15.c    
*    
* Description:  Converts the elements of the Q31 vector to Q15 vector.    
*    
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Redistribution and use in source and binary forms, with or without 
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the 
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.    
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

void arm_q31_to_q15(
  q31_t * pSrc,
  q15_t * pDst,
  uint32_t blockSize)
{
  q31_t *pIn = pSrc;                             /* Src pointer */
  uint32_t blkCnt;                               /* loop counter */

#ifndef ARM_MATH_CM0_FAMILY

  /* Run the below code for Cortex-M4 and Cortex-M3 */
  q31_t in1, in2, in3, in4;
  q31_t out1, out2;

  /*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 = (q15_t) A >> 16 */
    /* convert from q31 to q15 and then store the results in the destination buffer */
    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

    *__SIMD32(pDst)++ = out1;
    *__SIMD32(pDst)++ = out2;

    /* 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;

#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 = (q15_t) A >> 16 */
    /* convert from q31 to q15 and then store the results in the destination buffer */
    *pDst++ = (q15_t) (*pIn++ >> 16);

    /* Decrement the loop counter */
    blkCnt--;
  }

}