lib/main/CMSIS/DSP/Source/BasicMathFunctions/arm_shift_q31.c

   1 /* ----------------------------------------------------------------------
   2  * Project:      CMSIS DSP Library
   3  * Title:        arm_shift_q31.c
   4  * Description:  Shifts the elements of a Q31 vector by a specified number of bits
   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 groupMath
  33  */
  34 /**
  35  * @defgroup shift Vector Shift
  36  *
  37  * Shifts the elements of a fixed-point vector by a specified number of bits.
  38  * There are separate functions for Q7, Q15, and Q31 data types.
  39  * The underlying algorithm used is:
  40  *
  41  * <pre>
  42  *     pDst[n] = pSrc[n] << shift,   0 <= n < blockSize.
  43  * </pre>
  44  *
  45  * If <code>shift</code> is positive then the elements of the vector are shifted to the left.
  46  * If <code>shift</code> is negative then the elements of the vector are shifted to the right.
  47  *
  48  * The functions support in-place computation allowing the source and destination
  49  * pointers to reference the same memory buffer.
  50  */
  51
  52 /**
  53  * @addtogroup shift
  54  * @{
  55  */
  56
  57 /**
  58  * @brief  Shifts the elements of a Q31 vector a specified number of bits.
  59  * @param[in]  *pSrc points to the input vector
  60  * @param[in]  shiftBits number of bits to shift.  A positive value shifts left; a negative value shifts right.
  61  * @param[out]  *pDst points to the output vector
  62  * @param[in]  blockSize number of samples in the vector
  63  * @return none.
  64  *
  65  *
  66  * <b>Scaling and Overflow Behavior:</b>
  67  * \par
  68  * The function uses saturating arithmetic.
  69  * Results outside of the allowable Q31 range [0x80000000 0x7FFFFFFF] will be saturated.
  70  */
  71
  72 void arm_shift_q31(
  73   q31_t * pSrc,
  74   int8_t shiftBits,
  75   q31_t * pDst,
  76   uint32_t blockSize)
  77 {
  78   uint32_t blkCnt;                               /* loop counter */
  79   uint8_t sign = (shiftBits & 0x80);             /* Sign of shiftBits */
  80
  81 #if defined (ARM_MATH_DSP)
  82
  83   q31_t in1, in2, in3, in4;                      /* Temporary input variables */
  84   q31_t out1, out2, out3, out4;                  /* Temporary output variables */
  85
  86   /*loop Unrolling */
  87   blkCnt = blockSize >> 2U;
  88
  89
  90   if (sign == 0U)
  91   {
  92     /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
  93      ** a second loop below computes the remaining 1 to 3 samples. */
  94     while (blkCnt > 0U)
  95     {
  96       /* C = A  << shiftBits */
  97       /* Shift the input and then store the results in the destination buffer. */
  98       in1 = *pSrc;
  99       in2 = *(pSrc + 1);
 100       out1 = in1 << shiftBits;
 101       in3 = *(pSrc + 2);
 102       out2 = in2 << shiftBits;
 103       in4 = *(pSrc + 3);
 104       if (in1 != (out1 >> shiftBits))
 105         out1 = 0x7FFFFFFF ^ (in1 >> 31);
 106
 107       if (in2 != (out2 >> shiftBits))
 108         out2 = 0x7FFFFFFF ^ (in2 >> 31);
 109
 110       *pDst = out1;
 111       out3 = in3 << shiftBits;
 112       *(pDst + 1) = out2;
 113       out4 = in4 << shiftBits;
 114
 115       if (in3 != (out3 >> shiftBits))
 116         out3 = 0x7FFFFFFF ^ (in3 >> 31);
 117
 118       if (in4 != (out4 >> shiftBits))
 119         out4 = 0x7FFFFFFF ^ (in4 >> 31);
 120
 121       *(pDst + 2) = out3;
 122       *(pDst + 3) = out4;
 123
 124       /* Update destination pointer to process next sampels */
 125       pSrc += 4U;
 126       pDst += 4U;
 127
 128       /* Decrement the loop counter */
 129       blkCnt--;
 130     }
 131   }
 132   else
 133   {
 134
 135     /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
 136      ** a second loop below computes the remaining 1 to 3 samples. */
 137     while (blkCnt > 0U)
 138     {
 139       /* C = A >>  shiftBits */
 140       /* Shift the input and then store the results in the destination buffer. */
 141       in1 = *pSrc;
 142       in2 = *(pSrc + 1);
 143       in3 = *(pSrc + 2);
 144       in4 = *(pSrc + 3);
 145
 146       *pDst = (in1 >> -shiftBits);
 147       *(pDst + 1) = (in2 >> -shiftBits);
 148       *(pDst + 2) = (in3 >> -shiftBits);
 149       *(pDst + 3) = (in4 >> -shiftBits);
 150
 151
 152       pSrc += 4U;
 153       pDst += 4U;
 154
 155       blkCnt--;
 156     }
 157
 158   }
 159
 160   /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
 161    ** No loop unrolling is used. */
 162   blkCnt = blockSize % 0x4U;
 163
 164 #else
 165
 166   /* Run the below code for Cortex-M0 */
 167
 168
 169   /* Initialize blkCnt with number of samples */
 170   blkCnt = blockSize;
 171
 172 #endif /* #if defined (ARM_MATH_DSP) */
 173
 174
 175   while (blkCnt > 0U)
 176   {
 177     /* C = A (>> or <<) shiftBits */
 178     /* Shift the input and then store the result in the destination buffer. */
 179     *pDst++ = (sign == 0U) ? clip_q63_to_q31((q63_t) * pSrc++ << shiftBits) :
 180       (*pSrc++ >> -shiftBits);
 181
 182     /* Decrement the loop counter */
 183     blkCnt--;
 184   }
 185
 186
 187 }
 188
 189 /**
 190  * @} end of shift group
 191  */