DSP/Source/BasicMathFunctions/arm_scale_q15.c

/* ----------------------------------------------------------------------
 * Project:      CMSIS DSP Library
 * Title:        arm_scale_q15.c
 * Description:  Multiplies a Q15 vector by a scalar
 *
 * $Date:        27. January 2017
 * $Revision:    V.1.5.1
 *
 * Target Processor: Cortex-M cores
 * -------------------------------------------------------------------- */
/*
 * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "arm_math.h"

/**
 * @ingroup groupMath
 */

/**
 * @addtogroup scale
 * @{
 */

/**
 * @brief Multiplies a Q15 vector by a scalar.
 * @param[in]       *pSrc points to the input vector
 * @param[in]       scaleFract fractional portion of the scale value
 * @param[in]       shift number of bits to shift the result by
 * @param[out]      *pDst points to the output vector
 * @param[in]       blockSize number of samples in the vector
 * @return none.
 *
 * <b>Scaling and Overflow Behavior:</b>
 * \par
 * The input data <code>*pSrc</code> and <code>scaleFract</code> are in 1.15 format.
 * These are multiplied to yield a 2.30 intermediate result and this is shifted with saturation to 1.15 format.
 */


void arm_scale_q15(
  q15_t * pSrc,
  q15_t scaleFract,
  int8_t shift,
  q15_t * pDst,
  uint32_t blockSize)
{
  int8_t kShift = 15 - shift;                    /* shift to apply after scaling */
  uint32_t blkCnt;                               /* loop counter */

#if defined (ARM_MATH_DSP)

/* Run the below code for Cortex-M4 and Cortex-M3 */
  q15_t in1, in2, in3, in4;
  q31_t inA1, inA2;                              /* Temporary variables */
  q31_t out1, out2, out3, out4;


  /*loop Unrolling */
  blkCnt = blockSize >> 2U;

  /* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
   ** a second loop below computes the remaining 1 to 3 samples. */
  while (blkCnt > 0U)
  {
    /* Reading 2 inputs from memory */
    inA1 = *__SIMD32(pSrc)++;
    inA2 = *__SIMD32(pSrc)++;

    /* C = A * scale */
    /* Scale the inputs and then store the 2 results in the destination buffer
     * in single cycle by packing the outputs */
    out1 = (q31_t) ((q15_t) (inA1 >> 16) * scaleFract);
    out2 = (q31_t) ((q15_t) inA1 * scaleFract);
    out3 = (q31_t) ((q15_t) (inA2 >> 16) * scaleFract);
    out4 = (q31_t) ((q15_t) inA2 * scaleFract);

    /* apply shifting */
    out1 = out1 >> kShift;
    out2 = out2 >> kShift;
    out3 = out3 >> kShift;
    out4 = out4 >> kShift;

    /* saturate the output */
    in1 = (q15_t) (__SSAT(out1, 16));
    in2 = (q15_t) (__SSAT(out2, 16));
    in3 = (q15_t) (__SSAT(out3, 16));
    in4 = (q15_t) (__SSAT(out4, 16));

    /* store the result to destination */
    *__SIMD32(pDst)++ = __PKHBT(in2, in1, 16);
    *__SIMD32(pDst)++ = __PKHBT(in4, in3, 16);

    /* Decrement the loop counter */
    blkCnt--;
  }

  /* If the blockSize is not a multiple of 4, compute any remaining output samples here.
   ** No loop unrolling is used. */
  blkCnt = blockSize % 0x4U;

  while (blkCnt > 0U)
  {
    /* C = A * scale */
    /* Scale the input and then store the result in the destination buffer. */
    *pDst++ = (q15_t) (__SSAT(((*pSrc++) * scaleFract) >> kShift, 16));

    /* Decrement the loop counter */
    blkCnt--;
  }

#else

  /* Run the below code for Cortex-M0 */

  /* Initialize blkCnt with number of samples */
  blkCnt = blockSize;

  while (blkCnt > 0U)
  {
    /* C = A * scale */
    /* Scale the input and then store the result in the destination buffer. */
    *pDst++ = (q15_t) (__SSAT(((q31_t) * pSrc++ * scaleFract) >> kShift, 16));

    /* Decrement the loop counter */
    blkCnt--;
  }

#endif /* #if defined (ARM_MATH_DSP) */

}

/**
 * @} end of scale group
 */