arm_q31_to_q15.c

00001 /* ----------------------------------------------------------------------
00002  * Project:      CMSIS DSP Library
00003  * Title:        arm_q31_to_q15.c
00004  * Description:  Converts the elements of the Q31 vector to Q15 vector
00005  *
00006  * $Date:        27. January 2017
00007  * $Revision:    V.1.5.1
00008  *
00009  * Target Processor: Cortex-M cores
00010  * -------------------------------------------------------------------- */
00011 /*
00012  * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
00013  *
00014  * SPDX-License-Identifier: Apache-2.0
00015  *
00016  * Licensed under the Apache License, Version 2.0 (the License); you may
00017  * not use this file except in compliance with the License.
00018  * You may obtain a copy of the License at
00019  *
00020  * www.apache.org/licenses/LICENSE-2.0
00021  *
00022  * Unless required by applicable law or agreed to in writing, software
00023  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
00024  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00025  * See the License for the specific language governing permissions and
00026  * limitations under the License.
00027  */
00028 
00029 #include "arm_math.h"
00030 
00031 /**
00032  * @ingroup groupSupport
00033  */
00034 
00035 /**
00036  * @addtogroup q31_to_x
00037  * @{
00038  */
00039 
00040 /**
00041  * @brief Converts the elements of the Q31 vector to Q15 vector.
00042  * @param[in]       *pSrc points to the Q31 input vector
00043  * @param[out]      *pDst points to the Q15 output vector
00044  * @param[in]       blockSize length of the input vector
00045  * @return none.
00046  *
00047  * \par Description:
00048  *
00049  * The equation used for the conversion process is:
00050  *
00051  * <pre>
00052  *  pDst[n] = (q15_t) pSrc[n] >> 16;   0 <= n < blockSize.
00053  * </pre>
00054  *
00055  */
00056 
00057 
00058 void arm_q31_to_q15(
00059   q31_t * pSrc,
00060   q15_t * pDst,
00061   uint32_t blockSize)
00062 {
00063   q31_t *pIn = pSrc;                             /* Src pointer */
00064   uint32_t blkCnt;                               /* loop counter */
00065 
00066 #if defined (ARM_MATH_DSP)
00067 
00068   /* Run the below code for Cortex-M4 and Cortex-M3 */
00069   q31_t in1, in2, in3, in4;
00070   q31_t out1, out2;
00071 
00072   /*loop Unrolling */
00073   blkCnt = blockSize >> 2U;
00074 
00075   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
00076    ** a second loop below computes the remaining 1 to 3 samples. */
00077   while (blkCnt > 0U)
00078   {
00079     /* C = (q15_t) A >> 16 */
00080     /* convert from q31 to q15 and then store the results in the destination buffer */
00081     in1 = *pIn++;
00082     in2 = *pIn++;
00083     in3 = *pIn++;
00084     in4 = *pIn++;
00085 
00086     /* pack two higher 16-bit values from two 32-bit values */
00087 #ifndef ARM_MATH_BIG_ENDIAN
00088 
00089     out1 = __PKHTB(in2, in1, 16);
00090     out2 = __PKHTB(in4, in3, 16);
00091 
00092 #else
00093 
00094     out1 = __PKHTB(in1, in2, 16);
00095     out2 = __PKHTB(in3, in4, 16);
00096 
00097 #endif //      #ifdef ARM_MATH_BIG_ENDIAN
00098 
00099     *__SIMD32(pDst)++ = out1;
00100     *__SIMD32(pDst)++ = out2;
00101 
00102     /* Decrement the loop counter */
00103     blkCnt--;
00104   }
00105 
00106   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
00107    ** No loop unrolling is used. */
00108   blkCnt = blockSize % 0x4U;
00109 
00110 #else
00111 
00112   /* Run the below code for Cortex-M0 */
00113 
00114   /* Loop over blockSize number of values */
00115   blkCnt = blockSize;
00116 
00117 #endif /* #if defined (ARM_MATH_DSP) */
00118 
00119   while (blkCnt > 0U)
00120   {
00121     /* C = (q15_t) A >> 16 */
00122     /* convert from q31 to q15 and then store the results in the destination buffer */
00123     *pDst++ = (q15_t) (*pIn++ >> 16);
00124 
00125     /* Decrement the loop counter */
00126     blkCnt--;
00127   }
00128 
00129 }
00130 
00131 /**
00132  * @} end of q31_to_x group
00133  */
00134