mirror of
https://github.com/fluencelabs/musl
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74 lines
2.1 KiB
C
74 lines
2.1 KiB
C
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/* origin: FreeBSD /usr/src/lib/msun/src/s_tanh.c */
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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/* Tanh(x)
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* Return the Hyperbolic Tangent of x
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*
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* Method :
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* x -x
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* e - e
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* 0. tanh(x) is defined to be -----------
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* x -x
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* e + e
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* 1. reduce x to non-negative by tanh(-x) = -tanh(x).
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* 2. 0 <= x < 2**-28 : tanh(x) := x with inexact if x != 0
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* -t
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* 2**-28 <= x < 1 : tanh(x) := -----; t = expm1(-2x)
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* t + 2
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* 2
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* 1 <= x < 22 : tanh(x) := 1 - -----; t = expm1(2x)
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* t + 2
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* 22 <= x <= INF : tanh(x) := 1.
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*
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* Special cases:
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* tanh(NaN) is NaN;
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* only tanh(0)=0 is exact for finite argument.
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*/
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#include "libm.h"
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static const double one = 1.0, two = 2.0, tiny = 1.0e-300, huge = 1.0e300;
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double tanh(double x)
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{
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double t,z;
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int32_t jx,ix;
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GET_HIGH_WORD(jx, x);
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ix = jx & 0x7fffffff;
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/* x is INF or NaN */
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if (ix >= 0x7ff00000) {
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if (jx >= 0)
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return one/x + one; /* tanh(+-inf)=+-1 */
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else
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return one/x - one; /* tanh(NaN) = NaN */
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}
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if (ix < 0x40360000) { /* |x| < 22 */
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if (ix < 0x3e300000) { /* |x| < 2**-28 */
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/* tanh(tiny) = tiny with inexact */
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if (huge+x > one)
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return x;
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}
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if (ix >= 0x3ff00000) { /* |x| >= 1 */
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t = expm1(two*fabs(x));
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z = one - two/(t+two);
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} else {
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t = expm1(-two*fabs(x));
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z= -t/(t+two);
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}
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} else { /* |x| >= 22, return +-1 */
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z = one - tiny; /* raise inexact */
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}
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return jx >= 0 ? z : -z;
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}
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