diff options
Diffstat (limited to 'sysdeps/libm-ieee754/s_cbrtf.c')
| -rw-r--r-- | sysdeps/libm-ieee754/s_cbrtf.c | 118 |
1 files changed, 48 insertions, 70 deletions
diff --git a/sysdeps/libm-ieee754/s_cbrtf.c b/sysdeps/libm-ieee754/s_cbrtf.c index a2b3c8106c..f9f687c011 100644 --- a/sysdeps/libm-ieee754/s_cbrtf.c +++ b/sysdeps/libm-ieee754/s_cbrtf.c @@ -1,84 +1,62 @@ -/* s_cbrtf.c -- float version of s_cbrt.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. - * ==================================================== - */ - -#if defined(LIBM_SCCS) && !defined(lint) -static char rcsid[] = "$NetBSD: s_cbrtf.c,v 1.4 1995/05/10 20:46:51 jtc Exp $"; -#endif +/* Compute cubic root of float value. + Copyright (C) 1997 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Contributed by Dirk Alboth <dirka@uni-paderborn.de> and + Ulrich Drepper <drepper@cygnus.com>, 1997. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Library General Public License as + published by the Free Software Foundation; either version 2 of the + License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Library General Public License for more details. + + You should have received a copy of the GNU Library General Public + License along with the GNU C Library; see the file COPYING.LIB. If not, + write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, + Boston, MA 02111-1307, USA. */ #include "math.h" #include "math_private.h" -/* cbrtf(x) - * Return cube root of x - */ -#ifdef __STDC__ -static const unsigned -#else -static unsigned -#endif - B1 = 709958130, /* B1 = (84+2/3-0.03306235651)*2**23 */ - B2 = 642849266; /* B2 = (76+2/3-0.03306235651)*2**23 */ -#ifdef __STDC__ -static const float -#else -static float -#endif -C = 5.4285717010e-01, /* 19/35 = 0x3f0af8b0 */ -D = -7.0530611277e-01, /* -864/1225 = 0xbf348ef1 */ -E = 1.4142856598e+00, /* 99/70 = 0x3fb50750 */ -F = 1.6071428061e+00, /* 45/28 = 0x3fcdb6db */ -G = 3.5714286566e-01; /* 5/14 = 0x3eb6db6e */ +#define CBRT2 1.2599210498948731648 /* 2^(1/3) */ +#define SQR_CBRT2 1.5874010519681994748 /* 2^(2/3) */ + +static const double factor[5] = +{ + 1.0 / SQR_CBRT2, + 1.0 / CBRT2, + 1.0, + CBRT2, + SQR_CBRT2 +}; + -#ifdef __STDC__ - float __cbrtf(float x) -#else - float __cbrtf(x) - float x; -#endif +float +__cbrtf (float x) { - float r,s,t; - int32_t hx; - u_int32_t sign; - u_int32_t high; + float xm, ym, u, t2; + int xe; + + /* Reduce X. XM now is an range 1.0 to 0.5. */ + xm = __frexpf (fabsf (x), &xe); - GET_FLOAT_WORD(hx,x); - sign=hx&0x80000000; /* sign= sign(x) */ - hx ^=sign; - if(hx>=0x7f800000) return(x+x); /* cbrt(NaN,INF) is itself */ - if(hx==0) - return(x); /* cbrt(0) is itself */ + /* If X is not finite or is null return it (with raising exceptions + if necessary. */ + if (xe == 0) + return x + x; - SET_FLOAT_WORD(x,hx); /* x <- |x| */ - /* rough cbrt to 5 bits */ - if(hx<0x00800000) /* subnormal number */ - {SET_FLOAT_WORD(t,0x4b800000); /* set t= 2**24 */ - t*=x; GET_FLOAT_WORD(high,t); SET_FLOAT_WORD(t,high/3+B2); - } - else - SET_FLOAT_WORD(t,hx/3+B1); + u = (0.492659620528969547 + (0.697570460207922770 + - 0.191502161678719066 * xm) * xm); + t2 = u * u * u; - /* new cbrt to 23 bits */ - r=t*t/x; - s=C+r*t; - t*=G+F/(s+E+D/s); + ym = u * (t2 + 2.0 * xm) / (2.0 * t2 + xm) * factor[2 + xe % 3]; - /* retore the sign bit */ - GET_FLOAT_WORD(high,t); - SET_FLOAT_WORD(t,high|sign); - return(t); + return __ldexpf (x > 0.0 ? ym : -ym, xe / 3); } weak_alias (__cbrtf, cbrtf) |