/* @(#)e_cosh.c 1.3 95/01/18 */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunSoft, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* cosh(x) * Method : * mathematically cosh(x) if defined to be (exp(x)+exp(-x))/2 * 1. Replace x by |x| (cosh(x) = cosh(-x)). * 2. * [ exp(x) - 1 ]^2 * 0 <= x <= ln2/2 : cosh(x) := 1 + ------------------- * 2*exp(x) * * exp(x) + 1/exp(x) * ln2/2 <= x <= 22 : cosh(x) := ------------------- * 2 * 22 <= x <= lnovft : cosh(x) := exp(x)/2 * lnovft <= x <= ln2ovft: cosh(x) := exp(x/2)/2 * exp(x/2) * ln2ovft < x : cosh(x) := huge*huge (overflow) * * Special cases: * cosh(x) is |x| if x is +INF, -INF, or NaN. * only cosh(0)=1 is exact for finite x. */ #include #include "math_private.h" static const double one = 1.0, half=0.5, huge = 1.0e300; double cosh(double x) { double t,w; int32_t ix; uint32_t lx; /* High word of |x|. */ GET_HIGH_WORD(ix,x); ix &= 0x7fffffff; /* x is INF or NaN */ if(ix>=0x7ff00000) return x*x; /* |x| in [0,0.5*ln2], return 1+expm1(|x|)^2/(2*exp(|x|)) */ if(ix<0x3fd62e43) { t = expm1(fabs(x)); w = one+t; if (ix<0x3c800000) return w; /* cosh(tiny) = 1 */ return one+(t*t)/(w+w); } /* |x| in [0.5*ln2,22], return (exp(|x|)+1/exp(|x|)/2; */ if (ix < 0x40360000) { t = exp(fabs(x)); return half*t+half/t; } /* |x| in [22, log(maxdouble)] return half*exp(|x|) */ if (ix < 0x40862E42) return half*exp(fabs(x)); /* |x| in [log(maxdouble), overflowthresold] */ GET_LOW_WORD(lx,x); if (ix<0x408633CE || ((ix==0x408633ce)&&(lx<=(uint32_t)0x8fb9f87d))) { w = exp(half*fabs(x)); t = half*w; return t*w; } /* |x| > overflowthresold, cosh(x) overflow */ return huge*huge; }