arm_shift_q31.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_shift_q31.c  
00009 *  
00010 * Description:  Shifts the elements of a Q31 vector  
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 * Version 0.0.7  2010/06/10   
00027 *    Misra-C changes done  
00028 * -------------------------------------------------------------------- */ 
00029  
00030 #include "arm_math.h" 
00031  
00032 /**  
00033  * @ingroup groupMath  
00034  */ 
00035 /**  
00036  * @defgroup shift Vector Shift  
00037  *  
00038  * Shifts the elements of a fixed-point vector by a specified number of bits.  
00039  * There are separate functions for Q7, Q15, and Q31 data types.  
00040  * The underlying algorithm used is:  
00041  *  
00042  * <pre>  
00043  *     pDst[n] = pSrc[n] << shift,   0 <= n < blockSize.  
00044  * </pre>  
00045  *  
00046  * If <code>shift</code> is positive then the elements of the vector are shifted to the left.  
00047  * If <code>shift</code> is negative then the elements of the vector are shifted to the right.  
00048  */ 
00049  
00050 /**  
00051  * @addtogroup shift  
00052  * @{  
00053  */ 
00054  
00055 /**  
00056  * @brief  Shifts the elements of a Q31 vector a specified number of bits.  
00057  * @param  *pSrc points to the input vector  
00058  * @param  shiftBits number of bits to shift.  A positive value shifts left; a negative value shifts right.  
00059  * @param  *pDst points to the output vector  
00060  * @param  blockSize number of samples in the vector  
00061  * @return none.  
00062  *  
00063  *  
00064  * <b>Scaling and Overflow Behavior:</b>  
00065  * \par  
00066  * The function uses saturating arithmetic.  
00067  * Results outside of the allowable Q31 range [0x80000000 0x7FFFFFFF] will be saturated.  
00068  */ 
00069  
00070 void arm_shift_q31( 
00071   q31_t * pSrc, 
00072   int8_t shiftBits, 
00073   q31_t * pDst, 
00074   uint32_t blockSize) 
00075 { 
00076   uint32_t blkCnt;                               /* loop counter */ 
00077   uint32_t sign;                                 /* Sign of shiftBits */ 
00078  
00079  
00080   /*loop Unrolling */ 
00081   blkCnt = blockSize >> 2u; 
00082  
00083   /* Getting the sign of shiftBits */ 
00084   sign = (shiftBits & 0x80000000); 
00085  
00086   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.  
00087    ** a second loop below computes the remaining 1 to 3 samples. */ 
00088   while(blkCnt > 0u) 
00089   { 
00090     /* C = A (>> or <<) shiftBits */ 
00091     /* Shift the input and then store the results in the destination buffer. */ 
00092     *pDst++ = (sign == 0u) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) : 
00093                              (*pSrc++ >> -shiftBits); 
00094     *pDst++ = (sign == 0u) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) : 
00095                              (*pSrc++ >> -shiftBits); 
00096     *pDst++ = (sign == 0u) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) : 
00097                              (*pSrc++ >> -shiftBits); 
00098     *pDst++ = (sign == 0u) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) : 
00099                              (*pSrc++ >> -shiftBits); 
00100  
00101     /* Decrement the loop counter */ 
00102     blkCnt--; 
00103   } 
00104  
00105   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.  
00106    ** No loop unrolling is used. */ 
00107   blkCnt = blockSize % 0x4u; 
00108  
00109   while(blkCnt > 0u) 
00110   { 
00111     /* C = A (>> or <<) shiftBits */ 
00112     /* Shift the input and then store the result in the destination buffer. */ 
00113     *pDst++ = (sign == 0u) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) : 
00114                              (*pSrc++ >> -shiftBits); 
00115  
00116     /* Decrement the loop counter */ 
00117     blkCnt--; 
00118   } 
00119  
00120 } 
00121  
00122 /**  
00123  * @} end of shift group  
00124  */