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       ---
       s_tanhf.c (1436B)
       ---
            1 /* s_tanhf.c -- float version of s_tanh.c.
            2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
            3  */
            4 
            5 /*
            6  * ====================================================
            7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
            8  *
            9  * Developed at SunPro, a Sun Microsystems, Inc. business.
           10  * Permission to use, copy, modify, and distribute this
           11  * software is freely granted, provided that this notice
           12  * is preserved.
           13  * ====================================================
           14  */
           15 
           16 #ifndef lint
           17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_tanhf.c,v 1.7 2002/05/28 18:15:04 alfred Exp $";
           18 #endif
           19 
           20 #include "math.h"
           21 #include "math_private.h"
           22 
           23 static const float one=1.0, two=2.0, tiny = 1.0e-30;
           24 
           25 float
           26 tanhf(float x)
           27 {
           28         float t,z;
           29         int32_t jx,ix;
           30 
           31         GET_FLOAT_WORD(jx,x);
           32         ix = jx&0x7fffffff;
           33 
           34     /* x is INF or NaN */
           35         if(ix>=0x7f800000) {
           36             if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
           37             else       return one/x-one;    /* tanh(NaN) = NaN */
           38         }
           39 
           40     /* |x| < 22 */
           41         if (ix < 0x41b00000) {                /* |x|<22 */
           42             if (ix<0x24000000)                 /* |x|<2**-55 */
           43                 return x*(one+x);            /* tanh(small) = small */
           44             if (ix>=0x3f800000) {        /* |x|>=1  */
           45                 t = expm1f(two*fabsf(x));
           46                 z = one - two/(t+two);
           47             } else {
           48                 t = expm1f(-two*fabsf(x));
           49                 z= -t/(t+two);
           50             }
           51     /* |x| > 22, return +-1 */
           52         } else {
           53             z = one - tiny;                /* raised inexact flag */
           54         }
           55         return (jx>=0)? z: -z;
           56 }