log1pf4.h

Newlib 嵌入式 C库 标准实现代码

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#ifdef __SPU__
#ifndef _LOG1PF4_H_
#define _LOG1PF4_H_	1

#include <spu_intrinsics.h>
#include "simdmath.h"

#include "logf4.h"
#include "divf4.h"

/*
 * FUNCTION
 *	vector float _log1pf4(vector float x)
 *
 * DESCRIPTION
 *	The function _log1pf4 computes the natural logarithm of x + 1 
 *	for each of the float word elements of x.
 *
 *
 */

#define LOG1PF4_P0 0.0000000000000000000000000e+00f
#define LOG1PF4_P1 1.0000000000000000000000000e+00f
#define LOG1PF4_P2 1.4220868022897381610647471e+00f
#define LOG1PF4_P3 5.4254553902256308361984338e-01f
#define LOG1PF4_P4 4.5971908823142115796400731e-02f

#define LOG1PF4_Q0 1.0000000000000000000000000e+00f
#define LOG1PF4_Q1 1.9220868007537357247116461e+00f
#define LOG1PF4_Q2 1.1702556461286610645089468e+00f
#define LOG1PF4_Q3 2.4040413392943396631018516e-01f
#define LOG1PF4_Q4 1.0637426466449625625521058e-02f


static __inline vector float _log1pf4(vector float x) 
{
  vector float onef  = spu_splats(1.0f);
  vector float range = spu_splats(0.35f);
  vector unsigned int use_log;
  vector float pr, qr;
  vector float eresult;
  vector float rresult;
  vector float result;

  use_log = spu_cmpabsgt(x, range);

  /*
   * Calculate directly using log(x+1)
   */
  eresult = _logf4(spu_add(x, onef));

  /*
   * For x in [-0.35,0.35], use a rational approximation.
   */
  pr = spu_madd(x, spu_splats((float)LOG1PF4_P4), spu_splats((float)LOG1PF4_P3));
  qr = spu_madd(x, spu_splats((float)LOG1PF4_Q4), spu_splats((float)LOG1PF4_Q3));
  pr = spu_madd(pr, x, spu_splats((float)LOG1PF4_P2));
  qr = spu_madd(qr, x, spu_splats((float)LOG1PF4_Q2));
  pr = spu_madd(pr, x, spu_splats((float)LOG1PF4_P1));
  qr = spu_madd(qr, x, spu_splats((float)LOG1PF4_Q1));
  pr = spu_madd(pr, x, spu_splats((float)LOG1PF4_P0));
  qr = spu_madd(qr, x, spu_splats((float)LOG1PF4_Q0));
  rresult = _divf4(pr, qr);

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

  return result;
}

#endif /* _LOG1PF4_H_ */
#endif /* __SPU__ */