arm_q31_to_q15.c

00001 /* ----------------------------------------------------------------------------  
00002 * Copyright (C) 2010 ARM Limited. All rights reserved.  
00003 *  
00004 * $Date:        29. November 2010  
00005 * $Revision:    V1.0.3  
00006 *  
00007 * Project:      CMSIS DSP Library  
00008 * Title:        arm_q31_to_q15.c  
00009 *  
00010 * Description:  Processing function for the Conversion from Q31 to Q15  
00011 *  
00012 * Target Processor: Cortex-M4/Cortex-M3
00013 *  
00014 * Version 1.0.3 2010/11/29 
00015 *    Re-organized the CMSIS folders and updated documentation.  
00016 *   
00017 * Version 1.0.2 2010/11/11  
00018 *    Documentation updated.   
00019 *  
00020 * Version 1.0.1 2010/10/05   
00021 *    Production release and review comments incorporated.  
00022 *  
00023 * Version 1.0.0 2010/09/20   
00024 *    Production release and review comments incorporated.  
00025 * ---------------------------------------------------------------------------- */ 
00026  
00027 #include "arm_math.h" 
00028  
00029 /**  
00030  * @ingroup groupSupport  
00031  */ 
00032  
00033 /**  
00034  * @addtogroup q31_to_x  
00035  * @{  
00036  */ 
00037  
00038 /**  
00039  * @brief Converts the elements of the Q31 vector to Q15 vector.  
00040  * @param[in]       *pSrc points to the Q31 input vector  
00041  * @param[out]      *pDst points to the Q15 output vector 
00042  * @param[in]       blockSize length of the input vector  
00043  * @return none.  
00044  *   
00045  * \par Description:  
00046  *  
00047  * The equation used for the conversion process is:  
00048  * 
00049  * <pre>  
00050  *  pDst[n] = (q15_t) pSrc[n] >> 16;   0 <= n < blockSize.  
00051  * </pre>  
00052  * 
00053  */ 
00054  
00055  
00056 void arm_q31_to_q15( 
00057   q31_t * pSrc, 
00058   q15_t * pDst, 
00059   uint32_t blockSize) 
00060 { 
00061   q31_t *pIn = pSrc;                             /* Src pointer */ 
00062   uint32_t blkCnt;                               /* loop counter */ 
00063  
00064   /*loop Unrolling */ 
00065   blkCnt = blockSize >> 2u; 
00066  
00067   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
00068    ** a second loop below computes the remaining 1 to 3 samples. */ 
00069   while(blkCnt > 0u) 
00070   { 
00071     /* C = (q15_t) A >> 16 */ 
00072     /* convert from q31 to q15 and then store the results in the destination buffer */ 
00073     *pDst++ = (q15_t) (*pIn++ >> 16); 
00074     *pDst++ = (q15_t) (*pIn++ >> 16); 
00075     *pDst++ = (q15_t) (*pIn++ >> 16); 
00076     *pDst++ = (q15_t) (*pIn++ >> 16); 
00077  
00078     /* Decrement the loop counter */ 
00079     blkCnt--; 
00080   } 
00081  
00082   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
00083    ** No loop unrolling is used. */ 
00084   blkCnt = blockSize % 0x4u; 
00085  
00086   while(blkCnt > 0u) 
00087   { 
00088     /* C = (q15_t) A >> 16 */ 
00089     /* convert from q31 to q15 and then store the results in the destination buffer */ 
00090     *pDst++ = (q15_t) (*pIn++ >> 16); 
00091  
00092     /* Decrement the loop counter */ 
00093     blkCnt--; 
00094   } 
00095  
00096 } 
00097  
00098 /**  
00099  * @} end of q31_to_x group  
00100  */