sysdeps/ieee754/dbl-64/e_sinh.c

   1 /* @(#)e_sinh.c 5.1 93/09/24 */
   2 /*
   3  * ====================================================
   4  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   5  *
   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
   9  * is preserved.
  10  * ====================================================
  11  */
  12
  13 #if defined(LIBM_SCCS) && !defined(lint)
  14 static char rcsid[] = "$NetBSD: e_sinh.c,v 1.7 1995/05/10 20:46:13 jtc Exp $";
  15 #endif
  16
  17 /* __ieee754_sinh(x)
  18  * Method :
  19  * mathematically sinh(x) if defined to be (exp(x)-exp(-x))/2
  20  *      1. Replace x by |x| (sinh(-x) = -sinh(x)).
  21  *      2.
  22  *                                                  E + E/(E+1)
  23  *          0        <= x <= 22     :  sinh(x) := --------------, E=expm1(x)
  24  *                                                      2
  25  *
  26  *          22       <= x <= lnovft :  sinh(x) := exp(x)/2
  27  *          lnovft   <= x <= ln2ovft:  sinh(x) := exp(x/2)/2 * exp(x/2)
  28  *          ln2ovft  <  x           :  sinh(x) := x*shuge (overflow)
  29  *
  30  * Special cases:
  31  *      sinh(x) is |x| if x is +INF, -INF, or NaN.
  32  *      only sinh(0)=0 is exact for finite x.
  33  */
  34
  35 #include "math.h"
  36 #include "math_private.h"
  37
  38 #ifdef __STDC__
  39 static const double one = 1.0, shuge = 1.0e307;
  40 #else
  41 static double one = 1.0, shuge = 1.0e307;
  42 #endif
  43
  44 #ifdef __STDC__
  45         double __ieee754_sinh(double x)
  46 #else
  47         double __ieee754_sinh(x)
  48         double x;
  49 #endif
  50 {
  51         double t,w,h;
  52         int32_t ix,jx;
  53         u_int32_t lx;
  54
  55     /* High word of |x|. */
  56         GET_HIGH_WORD(jx,x);
  57         ix = jx&0x7fffffff;
  58
  59     /* x is INF or NaN */
  60         if(ix>=0x7ff00000) return x+x;
  61
  62         h = 0.5;
  63         if (jx<0) h = -h;
  64     /* |x| in [0,22], return sign(x)*0.5*(E+E/(E+1))) */
  65         if (ix < 0x40360000) {          /* |x|<22 */
  66             if (ix<0x3e300000)          /* |x|<2**-28 */
  67                 if(shuge+x>one) return x;/* sinh(tiny) = tiny with inexact */
  68             t = __expm1(fabs(x));
  69             if(ix<0x3ff00000) return h*(2.0*t-t*t/(t+one));
  70             return h*(t+t/(t+one));
  71         }
  72
  73     /* |x| in [22, log(maxdouble)] return 0.5*exp(|x|) */
  74         if (ix < 0x40862e42)  return h*__ieee754_exp(fabs(x));
  75
  76     /* |x| in [log(maxdouble), overflowthresold] */
  77         GET_LOW_WORD(lx,x);
  78         if (ix<0x408633ce || ((ix==0x408633ce)&&(lx<=(u_int32_t)0x8fb9f87d))) {
  79             w = __ieee754_exp(0.5*fabs(x));
  80             t = h*w;
  81             return t*w;
  82         }
  83
  84     /* |x| > overflowthresold, sinh(x) overflow */
  85         return x*shuge;
  86 }