| author | Rich Felker <dalias@aerifal.cx> | 2012年03月13日 01:17:53 -0400 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2012年03月13日 01:17:53 -0400 |
| commit | b69f695acedd4ce2798ef9ea28d834ceccc789bd (patch) | |
| tree | eafd98b9b75160210f3295ac074d699f863d958e /src/math/atanh.c | |
| parent | d46cf2e14cc4df7cc75e77d7009fcb6df1f48a33 (diff) | |
| download | musl-b69f695acedd4ce2798ef9ea28d834ceccc789bd.tar.gz | |
| -rw-r--r-- | src/math/atanh.c | 59 |
diff --git a/src/math/atanh.c b/src/math/atanh.c new file mode 100644 index 00000000..29290463 --- /dev/null +++ b/src/math/atanh.c @@ -0,0 +1,59 @@ +/* origin: FreeBSD /usr/src/lib/msun/src/e_atanh.c */ +/* + * ==================================================== + * 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. + * ==================================================== + * + */ +/* atanh(x) + * Method : + * 1.Reduced x to positive by atanh(-x) = -atanh(x) + * 2.For x>=0.5 + * 1 2x x + * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------) + * 2 1 - x 1 - x + * + * For x<0.5 + * atanh(x) = 0.5*log1p(2x+2x*x/(1-x)) + * + * Special cases: + * atanh(x) is NaN if |x| > 1 with signal; + * atanh(NaN) is that NaN with no signal; + * atanh(+-1) is +-INF with signal. + * + */ + +#include "libm.h" + +static const double one = 1.0, huge = 1e300; +static const double zero = 0.0; + +double atanh(double x) +{ + double t; + int32_t hx,ix; + uint32_t lx; + + EXTRACT_WORDS(hx, lx, x); + ix = hx & 0x7fffffff; + if ((ix | ((lx|-lx)>>31)) > 0x3ff00000) /* |x| > 1 */ + return (x-x)/(x-x); + if (ix == 0x3ff00000) + return x/zero; + if (ix < 0x3e300000 && (huge+x) > zero) /* x < 2**-28 */ + return x; + SET_HIGH_WORD(x, ix); + if (ix < 0x3fe00000) { /* x < 0.5 */ + t = x+x; + t = 0.5*log1p(t + t*x/(one-x)); + } else + t = 0.5*log1p((x+x)/(one-x)); + if (hx >= 0) + return t; + return -t; +} |