expm1f4.h

Newlib 嵌入式 C库 标准实现代码

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#ifdef __SPU__

#ifndef _EXPM1F4_H_
#define _EXPM1F4_H_	1

#include <spu_intrinsics.h>

#include "expf4.h"
#include "divf4.h"


#define EXPM1F4_P0 0.0000000000000000000000000e-00
#define EXPM1F4_P1 9.9999999999999988897769754e-01
#define EXPM1F4_P2 -6.5597409827762467697531701e-04
#define EXPM1F4_P3 2.3800889637330315679042414e-02
#define EXPM1F4_P4 -1.0914929910143700584950963e-05

#define EXPM1F4_Q0 1.0000000000000000000000000e-00
#define EXPM1F4_Q1 -5.0065597410018825019761834e-01
#define EXPM1F4_Q2 1.0746220997195164714721471e-01
#define EXPM1F4_Q3 -1.1966024153043854083566799e-02
#define EXPM1F4_Q4 5.9997727954467768105711878e-04


/*
 * FUNCTION
 *	vector float _expm1f4(vector float x)
 *
 *	_expm1d2 computes the exponential - 1 for each element
 *	of the input vector x.
 *
 *	This function is intended to return accurate values, even
 *	where exp(x) - 1 would normally produce bad results due to
 *	floating-point cancellation errors.
 *
 */

static __inline vector float _expm1f4(vector float x) 
{
  vector float onef  = spu_splats(1.0f);
  vector float rangelo = spu_splats(-0.4f);
  vector float rangehi = spu_splats(0.35f);
  vector unsigned int use_exp;
  vector float pr, qr;
  vector float eresult;
  vector float rresult;
  vector float result;

  use_exp = spu_or(spu_cmpgt(x, rangehi), spu_cmpgt(rangelo, x));

  /*
   * Calculate directly using exp(x) - 1
   */
  eresult = spu_sub(_expf4(x), onef);

  /*
   * For x in [-0.5,0.5], use a rational approximation.
   * The madd's are interleaved to reduce dependency stalls. Looks
   * like gcc is smart enough to do this on it's own... but why
   * take the chance.
   */
  pr = spu_madd(x, spu_splats((float)EXPM1F4_P4), spu_splats((float)EXPM1F4_P3));
  qr = spu_madd(x, spu_splats((float)EXPM1F4_Q4), spu_splats((float)EXPM1F4_Q3));
  pr = spu_madd(pr, x, spu_splats((float)EXPM1F4_P2));
  qr = spu_madd(qr, x, spu_splats((float)EXPM1F4_Q2));
  pr = spu_madd(pr, x, spu_splats((float)EXPM1F4_P1));
  qr = spu_madd(qr, x, spu_splats((float)EXPM1F4_Q1));
  pr = spu_madd(pr, x, spu_splats((float)EXPM1F4_P0));
  qr = spu_madd(qr, x, spu_splats((float)EXPM1F4_Q0));
  rresult = _divf4(pr, qr);

  /*
   * Select either direct calculation or rational approximation.
   */
  result = spu_sel(rresult, eresult, use_exp);

  return result;
}

#endif /* _EXPM1F4_H_ */
#endif /* __SPU__ */