MATHLIB_rsqrt.cpp

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#define ELEMENT_COUNT(x) c7x::element_count_of<x>::value
#define ELEMENT_TYPE(x) typename c7x::element_type_of<x>::type
 
/******************************************************************************/
/*                                                                            */
/* Includes                                                                   */
/*                                                                            */
/******************************************************************************/
 
#include "MATHLIB_types.h"
#include "MATHLIB_utility.h"
#include <cstddef>
 
/******************************************************************************/
/*                                                                            */
/* MATHLIB_rsqrt                                                                 */
/*                                                                            */
/******************************************************************************/
 
// this method performs rsqrt computation of input vector
template <typename T> MATHLIB_STATUS MATHLIB_rsqrt(size_t length, T *pSrc, T *pDst)
{
 
   // variables
   MATHLIB_STATUS status       = MATHLIB_SUCCESS; // return function status
   size_t         numBlocks    = 0;               // compute loop's iteration count
   size_t         remNumBlocks = 0;               // when numBlocks is not a multiple of SIMD width
 
   // derive c7x vector type from template typename
   typedef typename c7x::make_full_vector<T>::type vec;
 
   /* define type of elements vec vector holds as elemType */
   typedef ELEMENT_TYPE(vec) elemType;
 
   __SE_TEMPLATE_v1 se0Params = __gen_SE_TEMPLATE_v1();
   __SA_TEMPLATE_v1 sa0Params = __gen_SA_TEMPLATE_v1();
 
   status = MATHLIB_checkParams(length, pSrc, pDst);
 
   if (status == MATHLIB_SUCCESS) {
      MATHLIB_SE0SA01DSequentialInit(&se0Params, &sa0Params, length, pSrc, pDst);
 
      // calculate compute loop's iteration counter
      numBlocks    = length / c7x::element_count_of<vec>::value;
      remNumBlocks = length % c7x::element_count_of<vec>::value;
      if (remNumBlocks) {
         numBlocks++;
      }
 
      // open SE0, SE1, and SA0 for reading and writing operands
      MATHLIB_SE0SA0Open(&se0Params, &sa0Params, pSrc);
 
      /***********************************************************************/
      /* Create and assign values for constants employed on rsqrt computation */
      /***********************************************************************/
 
      vec half, OneP5, small, inf;
 
      half  = (vec) 0.5;
      OneP5 = (vec) 1.5;
      small = (vec) 1.17549435e-38f;
      inf   = (vec) 0x7F800000u;
 
      // compute loop to perform vector rsqrt
      for (size_t i = 0; i < numBlocks; i++) {
         vec inVec = c7x::strm_eng<0, vec>::get_adv();
 
         /**********************************************************************/
         /* Create variables employed on rsqrt computation                      */
         /**********************************************************************/
 
         vec x0, x1, x2, x3, outVec;
 
         /**********************************************************************/
         /* rsqrt computation                                                   */
         /**********************************************************************/
 
         // Reciprocal square root calculation
         x0 = __recip_sqrt(inVec);
         x1 = x0 * inVec;
         x3 = OneP5 - (x1 * x0 * half);
         x1 = x0 * x3;
         x2 = x1 * (OneP5 - (inVec * x1 * x1 * half));
 
         /**********************************************************************/
         /* Bounds checking                                                    */
         /**********************************************************************/
 
         // If input is <= 0, output defaults to 0
         __vpred cmp_lezero = __cmp_lt_pred(inVec, small);
         outVec             = __select(cmp_lezero, inf, x2);
 
         __vpred tmp  = c7x::strm_agen<0, vec>::get_vpred();
         vec    *addr = c7x::strm_agen<0, vec>::get_adv(pDst);
         __vstore_pred(tmp, addr, outVec);
      }
 
      MATHLIB_SE0SA0Close();
   }
 
   return status;
}
 
/******************************************************************************/
/*                                                                            */
/* Explicit templatization for datatypes supported by MATHLIB_rsqrt              */
/*                                                                            */
/******************************************************************************/
 
// single precision
template MATHLIB_STATUS MATHLIB_rsqrt<float>(size_t length, float *pSrc, float *pDst);
 
/******************************************************************************/
/*                                                                            */
/* C-interface wrapper functions                                              */
/*                                                                            */
/******************************************************************************/
 
extern "C" {
 
// single-precision wrapper
MATHLIB_STATUS MATHLIB_rsqrt_sp(size_t length, float *pSrc, float *pDst)
{
   MATHLIB_STATUS status = MATHLIB_rsqrt(length, pSrc, pDst);
   return status;
}
 
} // extern "C"