lib/main/CMSIS/DSP/Source/SupportFunctions/arm_q15_to_q7.c

   1 /* ----------------------------------------------------------------------
   2  * Project:      CMSIS DSP Library
   3  * Title:        arm_q15_to_q7.c
   4  * Description:  Converts the elements of the Q15 vector to Q7 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 q15_to_x
  37  * @{
  38  */
  39
  40
  41 /**
  42  * @brief Converts the elements of the Q15 vector to Q7 vector.
  43  * @param[in]       *pSrc points to the Q15 input vector
  44  * @param[out]      *pDst points to the Q7 output vector
  45  * @param[in]       blockSize length of the input vector
  46  * @return none.
  47  *
  48  * \par Description:
  49  *
  50  * The equation used for the conversion process is:
  51  *
  52  * <pre>
  53  *      pDst[n] = (q7_t) pSrc[n] >> 8;   0 <= n < blockSize.
  54  * </pre>
  55  *
  56  */
  57
  58
  59 void arm_q15_to_q7(
  60   q15_t * pSrc,
  61   q7_t * pDst,
  62   uint32_t blockSize)
  63 {
  64   q15_t *pIn = pSrc;                             /* Src pointer */
  65   uint32_t blkCnt;                               /* loop counter */
  66
  67 #if defined (ARM_MATH_DSP)
  68
  69   /* Run the below code for Cortex-M4 and Cortex-M3 */
  70   q31_t in1, in2;
  71   q31_t out1, out2;
  72
  73   /*loop Unrolling */
  74   blkCnt = blockSize >> 2U;
  75
  76   /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  77    ** a second loop below computes the remaining 1 to 3 samples. */
  78   while (blkCnt > 0U)
  79   {
  80     /* C = (q7_t) A >> 8 */
  81     /* convert from q15 to q7 and then store the results in the destination buffer */
  82     in1 = *__SIMD32(pIn)++;
  83     in2 = *__SIMD32(pIn)++;
  84
  85 #ifndef ARM_MATH_BIG_ENDIAN
  86
  87     out1 = __PKHTB(in2, in1, 16);
  88     out2 = __PKHBT(in2, in1, 16);
  89
  90 #else
  91
  92     out1 = __PKHTB(in1, in2, 16);
  93     out2 = __PKHBT(in1, in2, 16);
  94
  95 #endif //      #ifndef ARM_MATH_BIG_ENDIAN
  96
  97     /* rotate packed value by 24 */
  98     out2 = ((uint32_t) out2 << 8) | ((uint32_t) out2 >> 24);
  99
 100     /* anding with 0xff00ff00 to get two 8 bit values */
 101     out1 = out1 & 0xFF00FF00;
 102     /* anding with 0x00ff00ff to get two 8 bit values */
 103     out2 = out2 & 0x00FF00FF;
 104
 105     /* oring two values(contains two 8 bit values) to get four packed 8 bit values */
 106     out1 = out1 | out2;
 107
 108     /* store 4 samples at a time to destiantion buffer */
 109     *__SIMD32(pDst)++ = out1;
 110
 111     /* Decrement the loop counter */
 112     blkCnt--;
 113   }
 114
 115   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 116    ** No loop unrolling is used. */
 117   blkCnt = blockSize % 0x4U;
 118
 119 #else
 120
 121   /* Run the below code for Cortex-M0 */
 122
 123   /* Loop over blockSize number of values */
 124   blkCnt = blockSize;
 125
 126 #endif /* #if defined (ARM_MATH_DSP) */
 127
 128   while (blkCnt > 0U)
 129   {
 130     /* C = (q7_t) A >> 8 */
 131     /* convert from q15 to q7 and then store the results in the destination buffer */
 132     *pDst++ = (q7_t) (*pIn++ >> 8);
 133
 134     /* Decrement the loop counter */
 135     blkCnt--;
 136   }
 137
 138 }
 139
 140 /**
 141  * @} end of q15_to_x group
 142  */