Quelle k_tanf.cpp Sprache: C

/* k_tanf.c -- float version of k_tan.c
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
* Optimized by Bruce D. Evans.
*/

/*
* ====================================================
* Copyright 2004 Sun Microsystems, Inc.  All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/

#ifndef INLINE_KERNEL_TANDF
//#include <sys/cdefs.h>
//__FBSDID("$FreeBSD$");
#endif

#include "math_private.h"

/* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */
static const double
T[] =  {
  0x15554d3418c99f.0p-54, /* 0.333331395030791399758 */
  0x1112fd38999f72.0p-55, /* 0.133392002712976742718 */
  0x1b54c91d865afe.0p-57, /* 0.0533812378445670393523 */
  0x191df3908c33ce.0p-58, /* 0.0245283181166547278873 */
  0x185dadfcecf44e.0p-61, /* 0.00297435743359967304927 */
  0x1362b9bf971bcd.0p-59, /* 0.00946564784943673166728 */
};

#ifdef INLINE_KERNEL_TANDF
static __inline
#endif
float
__kernel_tandf(double x, int iy)
{
double z,r,w,s,t,u;

z =  x*x;
/*
* Split up the polynomial into small independent terms to give
* opportunities for parallel evaluation.  The chosen splitting is
* micro-optimized for Athlons (XP, X64).  It costs 2 multiplications
* relative to Horner's method on sequential machines.
*
* We add the small terms from lowest degree up for efficiency on
* non-sequential machines (the lowest degree terms tend to be ready
* earlier).  Apart from this, we don't care about order of
* operations, and don't need to care since we have precision to
* spare.  However, the chosen splitting is good for accuracy too,
* and would give results as accurate as Horner's method if the
* small terms were added from highest degree down.
*/
r = T[4]+z*T[5];
t = T[2]+z*T[3];
w = z*z;
s = z*x;
u = T[0]+z*T[1];
r = (x+s*u)+(s*w)*(t+w*r);
if(iy==1) return r;
else return -1.0/r;
}

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