lib/main/CMSIS/DSP/Source/SupportFunctions/arm_q31_to_q15.c

   1 /* ----------------------------------------------------------------------
   2  * Project:      CMSIS DSP Library
   3  * Title:        arm_q31_to_q15.c
   4  * Description:  Converts the elements of the Q31 vector to Q15 vector
   5  *
   6  * $Date:        27. January 2017
   7  * $Revision:    V.1.5.1
   8  *
   9  * Target Processor: Cortex-M cores
  10  * -------------------------------------------------------------------- */
  11 /*
  12  * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
  13  *
  14  * SPDX-License-Identifier: Apache-2.0
  15  *
  16  * Licensed under the Apache License, Version 2.0 (the License); you may
  17  * not use this file except in compliance with the License.
  18  * You may obtain a copy of the License at
  19  *
  20  * www.apache.org/licenses/LICENSE-2.0
  21  *
  22  * Unless required by applicable law or agreed to in writing, software
  23  * distributed under the License is distributed on an AS IS BASIS, WITHOUT
  24  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  25  * See the License for the specific language governing permissions and
  26  * limitations under the License.
  27  */
  28
  29 #include "arm_math.h"
  30
  31 /**
  32  * @ingroup groupSupport
  33  */
  34
  35 /**
  36  * @addtogroup q31_to_x
  37  * @{
  38  */
  39
  40 /**
  41  * @brief Converts the elements of the Q31 vector to Q15 vector.
  42  * @param[in]       *pSrc points to the Q31 input vector
  43  * @param[out]      *pDst points to the Q15 output vector
  44  * @param[in]       blockSize length of the input vector
  45  * @return none.
  46  *
  47  * \par Description:
  48  *
  49  * The equation used for the conversion process is:
  50  *
  51  * <pre>
  52  *      pDst[n] = (q15_t) pSrc[n] >> 16;   0 <= n < blockSize.
  53  * </pre>
  54  *
  55  */
  56
  57
  58 void arm_q31_to_q15(
  59   q31_t * pSrc,
  60   q15_t * pDst,
  61   uint32_t blockSize)
  62 {
  63   q31_t *pIn = pSrc;                             /* Src pointer */
  64   uint32_t blkCnt;                               /* loop counter */
  65
  66 #if defined (ARM_MATH_DSP)
  67
  68   /* Run the below code for Cortex-M4 and Cortex-M3 */
  69   q31_t in1, in2, in3, in4;
  70   q31_t out1, out2;
  71
  72   /*loop Unrolling */
  73   blkCnt = blockSize >> 2U;
  74
  75   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  76    ** a second loop below computes the remaining 1 to 3 samples. */
  77   while (blkCnt > 0U)
  78   {
  79     /* C = (q15_t) A >> 16 */
  80     /* convert from q31 to q15 and then store the results in the destination buffer */
  81     in1 = *pIn++;
  82     in2 = *pIn++;
  83     in3 = *pIn++;
  84     in4 = *pIn++;
  85
  86     /* pack two higher 16-bit values from two 32-bit values */
  87 #ifndef ARM_MATH_BIG_ENDIAN
  88
  89     out1 = __PKHTB(in2, in1, 16);
  90     out2 = __PKHTB(in4, in3, 16);
  91
  92 #else
  93
  94     out1 = __PKHTB(in1, in2, 16);
  95     out2 = __PKHTB(in3, in4, 16);
  96
  97 #endif //      #ifdef ARM_MATH_BIG_ENDIAN
  98
  99     *__SIMD32(pDst)++ = out1;
 100     *__SIMD32(pDst)++ = out2;
 101
 102     /* Decrement the loop counter */
 103     blkCnt--;
 104   }
 105
 106   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 107    ** No loop unrolling is used. */
 108   blkCnt = blockSize % 0x4U;
 109
 110 #else
 111
 112   /* Run the below code for Cortex-M0 */
 113
 114   /* Loop over blockSize number of values */
 115   blkCnt = blockSize;
 116
 117 #endif /* #if defined (ARM_MATH_DSP) */
 118
 119   while (blkCnt > 0U)
 120   {
 121     /* C = (q15_t) A >> 16 */
 122     /* convert from q31 to q15 and then store the results in the destination buffer */
 123     *pDst++ = (q15_t) (*pIn++ >> 16);
 124
 125     /* Decrement the loop counter */
 126     blkCnt--;
 127   }
 128
 129 }
 130
 131 /**
 132  * @} end of q31_to_x group
 133  */