arm_q15_to_q7.c

00001 /* ----------------------------------------------------------------------------    
00002 * Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
00003 *    
00004 * $Date:        19. March 2015
00005 * $Revision:    V.1.4.5  
00006 *    
00007 * Project:      CMSIS DSP Library    
00008 * Title:        arm_q15_to_q7.c    
00009 *    
00010 * Description:  Converts the elements of the Q15 vector to Q7 vector.  
00011 *    
00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
00013 *  
00014 * Redistribution and use in source and binary forms, with or without 
00015 * modification, are permitted provided that the following conditions
00016 * are met:
00017 *   - Redistributions of source code must retain the above copyright
00018 *     notice, this list of conditions and the following disclaimer.
00019 *   - Redistributions in binary form must reproduce the above copyright
00020 *     notice, this list of conditions and the following disclaimer in
00021 *     the documentation and/or other materials provided with the 
00022 *     distribution.
00023 *   - Neither the name of ARM LIMITED nor the names of its contributors
00024 *     may be used to endorse or promote products derived from this
00025 *     software without specific prior written permission.
00026 *
00027 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
00028 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
00029 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
00030 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
00031 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
00032 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
00033 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
00034 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
00035 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
00036 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
00037 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
00038 * POSSIBILITY OF SUCH DAMAGE.    
00039 * ---------------------------------------------------------------------------- */
00040 
00041 #include "arm_math.h"
00042 
00043 /**    
00044  * @ingroup groupSupport    
00045  */
00046 
00047 /**    
00048  * @addtogroup q15_to_x    
00049  * @{    
00050  */
00051 
00052 
00053 /**    
00054  * @brief Converts the elements of the Q15 vector to Q7 vector.     
00055  * @param[in]       *pSrc points to the Q15 input vector    
00056  * @param[out]      *pDst points to the Q7 output vector   
00057  * @param[in]       blockSize length of the input vector    
00058  * @return none.    
00059  *    
00060  * \par Description:    
00061  *    
00062  * The equation used for the conversion process is:    
00063  *   
00064  * <pre>    
00065  *  pDst[n] = (q7_t) pSrc[n] >> 8;   0 <= n < blockSize.    
00066  * </pre>   
00067  *   
00068  */
00069 
00070 
00071 void arm_q15_to_q7(
00072   q15_t * pSrc,
00073   q7_t * pDst,
00074   uint32_t blockSize)
00075 {
00076   q15_t *pIn = pSrc;                             /* Src pointer */
00077   uint32_t blkCnt;                               /* loop counter */
00078 
00079 #ifndef ARM_MATH_CM0_FAMILY
00080 
00081   /* Run the below code for Cortex-M4 and Cortex-M3 */
00082   q31_t in1, in2;
00083   q31_t out1, out2;
00084 
00085   /*loop Unrolling */
00086   blkCnt = blockSize >> 2u;
00087 
00088   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.    
00089    ** a second loop below computes the remaining 1 to 3 samples. */
00090   while(blkCnt > 0u)
00091   {
00092     /* C = (q7_t) A >> 8 */
00093     /* convert from q15 to q7 and then store the results in the destination buffer */
00094     in1 = *__SIMD32(pIn)++;
00095     in2 = *__SIMD32(pIn)++;
00096 
00097 #ifndef ARM_MATH_BIG_ENDIAN
00098 
00099     out1 = __PKHTB(in2, in1, 16);
00100     out2 = __PKHBT(in2, in1, 16);
00101 
00102 #else
00103 
00104     out1 = __PKHTB(in1, in2, 16);
00105     out2 = __PKHBT(in1, in2, 16);
00106 
00107 #endif //      #ifndef ARM_MATH_BIG_ENDIAN
00108 
00109     /* rotate packed value by 24 */
00110     out2 = ((uint32_t) out2 << 8) | ((uint32_t) out2 >> 24);
00111 
00112     /* anding with 0xff00ff00 to get two 8 bit values */
00113     out1 = out1 & 0xFF00FF00;
00114     /* anding with 0x00ff00ff to get two 8 bit values */
00115     out2 = out2 & 0x00FF00FF;
00116 
00117     /* oring two values(contains two 8 bit values) to get four packed 8 bit values */
00118     out1 = out1 | out2;
00119 
00120     /* store 4 samples at a time to destiantion buffer */
00121     *__SIMD32(pDst)++ = out1;
00122 
00123     /* Decrement the loop counter */
00124     blkCnt--;
00125   }
00126 
00127   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
00128    ** No loop unrolling is used. */
00129   blkCnt = blockSize % 0x4u;
00130 
00131 #else
00132 
00133   /* Run the below code for Cortex-M0 */
00134 
00135   /* Loop over blockSize number of values */
00136   blkCnt = blockSize;
00137 
00138 #endif /* #ifndef ARM_MATH_CM0_FAMILY */
00139 
00140   while(blkCnt > 0u)
00141   {
00142     /* C = (q7_t) A >> 8 */
00143     /* convert from q15 to q7 and then store the results in the destination buffer */
00144     *pDst++ = (q7_t) (*pIn++ >> 8);
00145 
00146     /* Decrement the loop counter */
00147     blkCnt--;
00148   }
00149 
00150 }
00151 
00152 /**    
00153  * @} end of q15_to_x group    
00154  */