src/math/s_tanhf.c

/* s_tanhf.c -- float version of s_tanh.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * 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 <math.h>
#include "math_private.h"

static const float one=1.0, two=2.0, tiny = 1.0e-30;

float
tanhf(float x)
{
        float t,z;
        int32_t jx,ix;

        GET_FLOAT_WORD(jx,x);
        ix = jx&0x7fffffff;

    /* x is INF or NaN */
        if(ix>=0x7f800000) {
            if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
            else       return one/x-one;    /* tanh(NaN) = NaN */
        }

    /* |x| < 22 */
        if (ix < 0x41b00000) {          /* |x|<22 */
            if (ix<0x24000000)          /* |x|<2**-55 */
                return x*(one+x);       /* tanh(small) = small */
            if (ix>=0x3f800000) {       /* |x|>=1  */
                t = expm1f(two*fabsf(x));
                z = one - two/(t+two);
            } else {
                t = expm1f(-two*fabsf(x));
                z= -t/(t+two);
            }
    /* |x| > 22, return +-1 */
        } else {
            z = one - tiny;             /* raised inexact flag */
        }
        return (jx>=0)? z: -z;
}