gonzui

    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: #include "math.h"
   17: #include "math_private.h"
   18: 
   19: static const float one=1.0, two=2.0, tiny = 1.0e-30;
   20: 
   21: float
   22: tanhf(float x)
   23: {
   24:         float t,z;
   25:         int32_t jx,ix;
   26: 
   27:         GET_FLOAT_WORD(jx,x);
   28:         ix = jx&0x7fffffff;
   29: 
   30:     /* x is INF or NaN */
   31:         if(ix>=0x7f800000) { 
   32:             if (jx>=0) return one/x+one;    /* tanh(+-inf)=+-1 */
   33:             else       return one/x-one;    /* tanh(NaN) = NaN */
   34:         }
   35: 
   36:     /* |x| < 22 */
   37:         if (ix < 0x41b00000) {         /* |x|<22 */
   38:             if (ix == 0)
   39:                 return x;             /* x == +-0 */
   40:             if (ix<0x24000000)                 /* |x|<2**-55 */
   41:                 return x*(one+x);     /* tanh(small) = small */
   42:             if (ix>=0x3f800000) {      /* |x|>=1  */
   43:                 t = expm1f(two*fabsf(x));
   44:                 z = one - two/(t+two);
   45:             } else {
   46:                 t = expm1f(-two*fabsf(x));
   47:                 z= -t/(t+two);
   48:             }
   49:     /* |x| > 22, return +-1 */
   50:         } else {
   51:             z = one - tiny;            /* raised inexact flag */
   52:         }
   53:         return (jx>=0)? z: -z;
   54: }