diff options
Diffstat (limited to 'sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c')
-rw-r--r-- | sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c | 104 |
1 files changed, 100 insertions, 4 deletions
diff --git a/sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c b/sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c index 010a671dce..317d238057 100644 --- a/sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c +++ b/sysdeps/ieee754/ldbl-128ibm/s_cbrtl.c @@ -1,6 +1,102 @@ -/* Looks like we can use ieee854 s_cbrtl.c as is for IBM extended format. */ +/* Implementation of cbrtl. IBM Extended Precision version. + Cephes Math Library Release 2.2: January, 1991 + Copyright 1984, 1991 by Stephen L. Moshier + Adapted for glibc October, 2001. + + This library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + This 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 + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with this library; if not, see + <http://www.gnu.org/licenses/>. */ + +/* This file was copied from sysdeps/ieee754/ldbl-128/e_j0l.c. */ + + #include <math_ldbl_opt.h> -#undef weak_alias -#define weak_alias(n,a) -#include <sysdeps/ieee754/ldbl-128/s_cbrtl.c> +#include <math.h> +#include <math_private.h> + +static const long double CBRT2 = 1.259921049894873164767210607278228350570251L; +static const long double CBRT4 = 1.587401051968199474751705639272308260391493L; +static const long double CBRT2I = 0.7937005259840997373758528196361541301957467L; +static const long double CBRT4I = 0.6299605249474365823836053036391141752851257L; + + +long double +__cbrtl (long double x) +{ + int e, rem, sign; + long double z; + + if (!isfinite (x)) + return x + x; + + if (x == 0) + return (x); + + if (x > 0) + sign = 1; + else + { + sign = -1; + x = -x; + } + + z = x; + /* extract power of 2, leaving mantissa between 0.5 and 1 */ + x = __frexpl (x, &e); + + /* Approximate cube root of number between .5 and 1, + peak relative error = 1.2e-6 */ + x = ((((1.3584464340920900529734e-1L * x + - 6.3986917220457538402318e-1L) * x + + 1.2875551670318751538055e0L) * x + - 1.4897083391357284957891e0L) * x + + 1.3304961236013647092521e0L) * x + 3.7568280825958912391243e-1L; + + /* exponent divided by 3 */ + if (e >= 0) + { + rem = e; + e /= 3; + rem -= 3 * e; + if (rem == 1) + x *= CBRT2; + else if (rem == 2) + x *= CBRT4; + } + else + { /* argument less than 1 */ + e = -e; + rem = e; + e /= 3; + rem -= 3 * e; + if (rem == 1) + x *= CBRT2I; + else if (rem == 2) + x *= CBRT4I; + e = -e; + } + + /* multiply by power of 2 */ + x = __ldexpl (x, e); + + /* Newton iteration */ + x -= (x - (z / (x * x))) * 0.3333333333333333333333333333333333333333L; + x -= (x - (z / (x * x))) * 0.3333333333333333333333333333333333333333L; + x -= (x - (z / (x * x))) * 0.3333333333333333333333333333333333333333L; + + if (sign < 0) + x = -x; + return (x); +} + long_double_symbol (libm, __cbrtl, cbrtl); |