newlib/newlib/libm/machine/spu/headers/erfd2.h

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/* PROLOG END TAG zYx                                              */
#ifdef __SPU__
#ifndef _ERFD2_H_
#define _ERFD2_H_	1

#include <spu_intrinsics.h>

#include "expd2.h"
#include "recipd2.h"
#include "divd2.h"
#include "erf_utils.h"

/*
 * FUNCTION
 *  vector double _erfd2(vector double x)
 *
 * DESCRIPTION
 *  The erfd2 function computes the error function of each element of x.
 *
 *  C99 Special Cases:
 *  - erf(+0) returns +0
 *  - erf(-0) returns -0
 *  - erf(+infinite) returns +1
 *  - erf(-infinite) returns -1
 *
 *  Other Cases:
 *  - erf(Nan) returns Nan
 *
 */

static __inline vector double _erfd2(vector double x)
{
  vec_uchar16 dup_even  = ((vec_uchar16) { 0,1,2,3, 0,1,2,3,  8, 9,10,11,  8, 9,10,11 });
  vec_double2 onehalfd  = spu_splats(0.5);
  vec_double2 oned      = spu_splats(1.0);
  vec_double2 sign_mask = spu_splats(-0.0);

  /* This is where we switch from Taylor Series to Continued Fraction approximation */
  vec_float4 approx_point = spu_splats(1.77f);

  vec_double2 xabs, xsqu, xsign;
  vec_double2 tresult, presult, result;

  xsign = spu_and(x, sign_mask);
  xabs = spu_andc(x, sign_mask);
  xsqu = spu_mul(x, x);

  /*
   * Taylor Series Expansion near Zero
   */
  TAYLOR_ERF(xabs, xsqu, tresult);

  /*
   * Continued Fraction Approximation of Erfc().
   * erf = 1 - erfc 
   */
  CONTFRAC_ERFC(xabs, xsqu, presult);
  presult = spu_sub(oned, presult);


  /*
   * Select the appropriate approximation.
   */
  vec_float4 xf = spu_roundtf(xabs);
  xf = spu_shuffle(xf, xf, dup_even);
  result = spu_sel(tresult, presult, (vec_ullong2)spu_cmpgt(xf, approx_point));


  /*
   * Special cases/errors.
   */

  /* x = +/- infinite, return +/-1 */
  /* x = nan, return x */
  result = spu_sel(result, oned, spu_testsv(x, SPU_SV_NEG_INFINITY | SPU_SV_POS_INFINITY));
  result = spu_sel(result,    x, spu_testsv(x, SPU_SV_NEG_DENORM   | SPU_SV_POS_DENORM));

  /*
   * Preserve sign in result, since erf(-x) = -erf(x)
   */
  result = spu_or(result, xsign);

  return result;
}

#endif /* _ERFD2_H_ */
#endif /* __SPU__ */