DSP_Lib/Source/BasicMathFunctions/arm_scale_q15.c

/* ----------------------------------------------------------------------    
* Copyright (C) 2010-2014 ARM Limited. All rights reserved.    
*    
* $Date:        19. March 2015
* $Revision: 	V.1.4.5
*    
* Project: 	    CMSIS DSP Library    
* Title:		arm_scale_q15.c    
*    
* Description:	Multiplies a Q15 vector by a scalar.    
*    
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*  
* Redistribution and use in source and binary forms, with or without 
* modification, are permitted provided that the following conditions
* are met:
*   - Redistributions of source code must retain the above copyright
*     notice, this list of conditions and the following disclaimer.
*   - Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in
*     the documentation and/or other materials provided with the 
*     distribution.
*   - Neither the name of ARM LIMITED nor the names of its contributors
*     may be used to endorse or promote products derived from this
*     software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* -------------------------------------------------------------------- */

#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 */

#ifndef ARM_MATH_CM0_FAMILY

/* 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 /* #ifndef ARM_MATH_CM0_FAMILY */

}

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