1 /* @(#)s_tanh.c 5.1 93/09/24 */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
10 * ====================================================
14 static char rcsid
[] = "$FreeBSD: src/lib/msun/src/s_tanh.c,v 1.9 2008/02/22 02:30:36 das Exp $";
18 * Return the Hyperbolic Tangent of x
23 * 0. tanh(x) is defined to be -----------
26 * 1. reduce x to non-negative by tanh(-x) = -tanh(x).
27 * 2. 0 <= x < 2**-28 : tanh(x) := x with inexact if x != 0
29 * 2**-28 <= x < 1 : tanh(x) := -----; t = expm1(-2x)
32 * 1 <= x < 22 : tanh(x) := 1 - -----; t = expm1(2x)
34 * 22 <= x <= INF : tanh(x) := 1.
38 * only tanh(0)=0 is exact for finite argument.
43 #include "math_private.h"
45 static const volatile double tiny
__attribute__ ((__section__(".rodata"))) = 1.0e-300;
46 static const double one
= 1.0, two
= 2.0, huge
= 1.0e300
;
59 if (jx
>=0) return one
/x
+one
; /* tanh(+-inf)=+-1 */
60 else return one
/x
-one
; /* tanh(NaN) = NaN */
64 if (ix
< 0x40360000) { /* |x|<22 */
65 if (ix
<0x3e300000) { /* |x|<2**-28 */
66 if(huge
+x
>one
) return x
; /* tanh(tiny) = tiny with inexact */
68 if (ix
>=0x3ff00000) { /* |x|>=1 */
69 t
= expm1(two
*fabs(x
));
70 z
= one
- two
/(t
+two
);
72 t
= expm1(-two
*fabs(x
));
75 /* |x| >= 22, return +-1 */
77 z
= one
- tiny
; /* raise inexact flag */
79 return (jx
>=0)? z
: -z
;
82 #if (LDBL_MANT_DIG == 53)
83 AROS_MAKE_ASM_SYM(typeof(tanhl
), tanhl
, AROS_CSYM_FROM_ASM_NAME(tanhl
), AROS_CSYM_FROM_ASM_NAME(tanh
));
84 AROS_EXPORT_ASM_SYM(AROS_CSYM_FROM_ASM_NAME(tanhl
));