arm_q15_to_q7.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_q15_to_q7.c  
00009 *  
00010 * Description:  Processing function for the Conversion from Q15 to Q7  
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 q15_to_x  
00035  * @{  
00036  */ 
00037  
00038  
00039 /**  
00040  * @brief Converts the elements of the Q15 vector to Q7 vector.   
00041  * @param[in]       *pSrc points to the Q15 input vector  
00042  * @param[out]      *pDst points to the Q7 output vector 
00043  * @param[in]       blockSize length of the input vector  
00044  * @return none.  
00045  *  
00046  * \par Description:  
00047  *  
00048  * The equation used for the conversion process is:  
00049  * 
00050  * <pre>  
00051  *  pDst[n] = (q7_t) pSrc[n] >> 8;   0 <= n < blockSize.  
00052  * </pre> 
00053  * 
00054  */ 
00055  
00056  
00057 void arm_q15_to_q7( 
00058   q15_t * pSrc, 
00059   q7_t * pDst, 
00060   uint32_t blockSize) 
00061 { 
00062   q15_t *pIn = pSrc;                             /* Src pointer */ 
00063   uint32_t blkCnt;                               /* loop counter */ 
00064  
00065   /*loop Unrolling */ 
00066   blkCnt = blockSize >> 2u; 
00067  
00068   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
00069    ** a second loop below computes the remaining 1 to 3 samples. */ 
00070   while(blkCnt > 0u) 
00071   { 
00072     /* C = (q7_t) A >> 8 */ 
00073     /* convert from q15 to q7 and then store the results in the destination buffer */ 
00074     *pDst++ = (q7_t) (*pIn++ >> 8); 
00075     *pDst++ = (q7_t) (*pIn++ >> 8); 
00076     *pDst++ = (q7_t) (*pIn++ >> 8); 
00077     *pDst++ = (q7_t) (*pIn++ >> 8); 
00078  
00079     /* Decrement the loop counter */ 
00080     blkCnt--; 
00081   } 
00082  
00083   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
00084    ** No loop unrolling is used. */ 
00085   blkCnt = blockSize % 0x4u; 
00086  
00087   while(blkCnt > 0u) 
00088   { 
00089     /* C = (q7_t) A >> 8 */ 
00090     /* convert from q15 to q7 and then store the results in the destination buffer */ 
00091     *pDst++ = (q7_t) (*pIn++ >> 8); 
00092  
00093     /* Decrement the loop counter */ 
00094     blkCnt--; 
00095   } 
00096  
00097 } 
00098  
00099 /**  
00100  * @} end of q15_to_x group  
00101  */