55 lines
1.8 KiB
C
55 lines
1.8 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/k_tanf.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.
|
|
* ====================================================
|
|
*/
|
|
|
|
#include "libc/math/libm.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 */
|
|
};
|
|
|
|
float __tandf(double x, int odd)
|
|
{
|
|
double_t 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 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);
|
|
return odd ? -1.0/r : r;
|
|
}
|