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  1. /* ----------------------------------------------------------------------------    
  2. * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
  3. *    
  4. * $Date:        19. March 2015
  5. * $Revision:    V.1.4.5  
  6. *    
  7. * Project:          CMSIS DSP Library    
  8. * Title:                arm_q15_to_q7.c    
  9. *    
  10. * Description:  Converts the elements of the Q15 vector to Q7 vector.  
  11. *    
  12. * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
  13. *  
  14. * Redistribution and use in source and binary forms, with or without
  15. * modification, are permitted provided that the following conditions
  16. * are met:
  17. *   - Redistributions of source code must retain the above copyright
  18. *     notice, this list of conditions and the following disclaimer.
  19. *   - Redistributions in binary form must reproduce the above copyright
  20. *     notice, this list of conditions and the following disclaimer in
  21. *     the documentation and/or other materials provided with the
  22. *     distribution.
  23. *   - Neither the name of ARM LIMITED nor the names of its contributors
  24. *     may be used to endorse or promote products derived from this
  25. *     software without specific prior written permission.
  26. *
  27. * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  28. * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  29. * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  30. * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  31. * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  32. * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  33. * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  34. * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  35. * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36. * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  37. * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  38. * POSSIBILITY OF SUCH DAMAGE.    
  39. * ---------------------------------------------------------------------------- */
  40.  
  41. #include "arm_math.h"
  42.  
  43. /**    
  44.  * @ingroup groupSupport    
  45.  */
  46.  
  47. /**    
  48.  * @addtogroup q15_to_x    
  49.  * @{    
  50.  */
  51.  
  52.  
  53. /**    
  54.  * @brief Converts the elements of the Q15 vector to Q7 vector.    
  55.  * @param[in]       *pSrc points to the Q15 input vector    
  56.  * @param[out]      *pDst points to the Q7 output vector  
  57.  * @param[in]       blockSize length of the input vector    
  58.  * @return none.    
  59.  *    
  60.  * \par Description:    
  61.  *    
  62.  * The equation used for the conversion process is:    
  63.  *  
  64.  * <pre>    
  65.  *      pDst[n] = (q7_t) pSrc[n] >> 8;   0 <= n < blockSize.    
  66.  * </pre>  
  67.  *  
  68.  */
  69.  
  70.  
  71. void arm_q15_to_q7(
  72.   q15_t * pSrc,
  73.   q7_t * pDst,
  74.   uint32_t blockSize)
  75. {
  76.   q15_t *pIn = pSrc;                             /* Src pointer */
  77.   uint32_t blkCnt;                               /* loop counter */
  78.  
  79. #ifndef ARM_MATH_CM0_FAMILY
  80.  
  81.   /* Run the below code for Cortex-M4 and Cortex-M3 */
  82.   q31_t in1, in2;
  83.   q31_t out1, out2;
  84.  
  85.   /*loop Unrolling */
  86.   blkCnt = blockSize >> 2u;
  87.  
  88.   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
  89.    ** a second loop below computes the remaining 1 to 3 samples. */
  90.   while(blkCnt > 0u)
  91.   {
  92.     /* C = (q7_t) A >> 8 */
  93.     /* convert from q15 to q7 and then store the results in the destination buffer */
  94.     in1 = *__SIMD32(pIn)++;
  95.     in2 = *__SIMD32(pIn)++;
  96.  
  97. #ifndef ARM_MATH_BIG_ENDIAN
  98.  
  99.     out1 = __PKHTB(in2, in1, 16);
  100.     out2 = __PKHBT(in2, in1, 16);
  101.  
  102. #else
  103.  
  104.     out1 = __PKHTB(in1, in2, 16);
  105.     out2 = __PKHBT(in1, in2, 16);
  106.  
  107. #endif //      #ifndef ARM_MATH_BIG_ENDIAN
  108.  
  109.     /* rotate packed value by 24 */
  110.     out2 = ((uint32_t) out2 << 8) | ((uint32_t) out2 >> 24);
  111.  
  112.     /* anding with 0xff00ff00 to get two 8 bit values */
  113.     out1 = out1 & 0xFF00FF00;
  114.     /* anding with 0x00ff00ff to get two 8 bit values */
  115.     out2 = out2 & 0x00FF00FF;
  116.  
  117.     /* oring two values(contains two 8 bit values) to get four packed 8 bit values */
  118.     out1 = out1 | out2;
  119.  
  120.     /* store 4 samples at a time to destiantion buffer */
  121.     *__SIMD32(pDst)++ = out1;
  122.  
  123.     /* Decrement the loop counter */
  124.     blkCnt--;
  125.   }
  126.  
  127.   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
  128.    ** No loop unrolling is used. */
  129.   blkCnt = blockSize % 0x4u;
  130.  
  131. #else
  132.  
  133.   /* Run the below code for Cortex-M0 */
  134.  
  135.   /* Loop over blockSize number of values */
  136.   blkCnt = blockSize;
  137.  
  138. #endif /* #ifndef ARM_MATH_CM0_FAMILY */
  139.  
  140.   while(blkCnt > 0u)
  141.   {
  142.     /* C = (q7_t) A >> 8 */
  143.     /* convert from q15 to q7 and then store the results in the destination buffer */
  144.     *pDst++ = (q7_t) (*pIn++ >> 8);
  145.  
  146.     /* Decrement the loop counter */
  147.     blkCnt--;
  148.   }
  149.  
  150. }
  151.  
  152. /**    
  153.  * @} end of q15_to_x group    
  154.  */
  155.