diff options
Diffstat (limited to 'src/math/atanhf.c')
| -rw-r--r-- | src/math/atanhf.c | 50 |
1 files changed, 14 insertions, 36 deletions
diff --git a/src/math/atanhf.c b/src/math/atanhf.c index 2be780bb..ca106efc 100644 --- a/src/math/atanhf.c +++ b/src/math/atanhf.c @@ -1,42 +1,20 @@ -/* origin: FreeBSD /usr/src/lib/msun/src/e_atanhf.c */ -/* - * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. - */ -/* - * ==================================================== - * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. - * - * Developed at SunPro, a Sun Microsystems, Inc. business. - * Permission to use, copy, modify, and distribute this - * software is freely granted, provided that this notice - * is preserved. - * ==================================================== - */ - #include "libm.h" -static const float huge = 1e30; - +/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */ float atanhf(float x) { - float t; - int32_t hx,ix; + union {float f; uint32_t i;} u = {.f = x}; + unsigned s = u.i >> 31; + + /* |x| */ + u.i &= 0x7fffffff; + x = u.f; - GET_FLOAT_WORD(hx, x); - ix = hx & 0x7fffffff; - if (ix > 0x3f800000) /* |x| > 1 */ - return (x-x)/(x-x); - if (ix == 0x3f800000) - return x/0.0f; - if (ix < 0x31800000 && huge+x > 0.0f) /* x < 2**-28 */ - return x; - SET_FLOAT_WORD(x, ix); - if (ix < 0x3f000000) { /* x < 0.5 */ - t = x+x; - t = 0.5f*log1pf(t + t*x/(1.0f-x)); - } else - t = 0.5f*log1pf((x+x)/(1.0f-x)); - if (hx >= 0) - return t; - return -t; + if (u.i < 0x3f800000 - (1<<23)) { + /* |x| < 0.5, up to 1.7ulp error */ + x = 0.5f*log1pf(2*x + 2*x*x/(1-x)); + } else { + x = 0.5f*log1pf(2*x/(1-x)); + } + return s ? -x : x; } |