mirror of
https://git.planet-casio.com/Lephenixnoir/OpenLibm.git
synced 2025-01-01 06:23:39 +01:00
78 lines
2 KiB
C
78 lines
2 KiB
C
/* @(#)s_tanh.c 5.1 93/09/24 */
|
|
/*
|
|
* ====================================================
|
|
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
|
|
*
|
|
* Developed at SunPro, a Sun Microsystems, Inc. business.
|
|
* Permission to use, copy, modify, and distribute this
|
|
* software is freely granted, provided that this notice
|
|
* is preserved.
|
|
* ====================================================
|
|
*/
|
|
|
|
#include "cdefs-compat.h"
|
|
//__FBSDID("$FreeBSD: src/lib/msun/src/s_tanh.c,v 1.9 2008/02/22 02:30:36 das Exp $");
|
|
|
|
/* Tanh(x)
|
|
* Return the Hyperbolic Tangent of x
|
|
*
|
|
* Method :
|
|
* x -x
|
|
* e - e
|
|
* 0. tanh(x) is defined to be -----------
|
|
* x -x
|
|
* e + e
|
|
* 1. reduce x to non-negative by tanh(-x) = -tanh(x).
|
|
* 2. 0 <= x < 2**-28 : tanh(x) := x with inexact if x != 0
|
|
* -t
|
|
* 2**-28 <= x < 1 : tanh(x) := -----; t = expm1(-2x)
|
|
* t + 2
|
|
* 2
|
|
* 1 <= x < 22 : tanh(x) := 1 - -----; t = expm1(2x)
|
|
* t + 2
|
|
* 22 <= x <= INF : tanh(x) := 1.
|
|
*
|
|
* Special cases:
|
|
* tanh(NaN) is NaN;
|
|
* only tanh(0)=0 is exact for finite argument.
|
|
*/
|
|
|
|
#include <openlibm_math.h>
|
|
|
|
#include "math_private.h"
|
|
|
|
static const double one = 1.0, two = 2.0, tiny = 1.0e-300, huge = 1.0e300;
|
|
|
|
OLM_DLLEXPORT double
|
|
tanh(double x)
|
|
{
|
|
double t,z;
|
|
int32_t jx,ix;
|
|
|
|
GET_HIGH_WORD(jx,x);
|
|
ix = jx&0x7fffffff;
|
|
|
|
/* x is INF or NaN */
|
|
if(ix>=0x7ff00000) {
|
|
if (jx>=0) return one/x+one; /* tanh(+-inf)=+-1 */
|
|
else return one/x-one; /* tanh(NaN) = NaN */
|
|
}
|
|
|
|
/* |x| < 22 */
|
|
if (ix < 0x40360000) { /* |x|<22 */
|
|
if (ix<0x3e300000) { /* |x|<2**-28 */
|
|
if(huge+x>one) return x; /* tanh(tiny) = tiny with inexact */
|
|
}
|
|
if (ix>=0x3ff00000) { /* |x|>=1 */
|
|
t = expm1(two*fabs(x));
|
|
z = one - two/(t+two);
|
|
} else {
|
|
t = expm1(-two*fabs(x));
|
|
z= -t/(t+two);
|
|
}
|
|
/* |x| >= 22, return +-1 */
|
|
} else {
|
|
z = one - tiny; /* raise inexact flag */
|
|
}
|
|
return (jx>=0)? z: -z;
|
|
}
|