diff options
Diffstat (limited to 'sysdeps/libm-ieee754/s_csqrt.c')
| -rw-r--r-- | sysdeps/libm-ieee754/s_csqrt.c | 31 |
1 files changed, 17 insertions, 14 deletions
diff --git a/sysdeps/libm-ieee754/s_csqrt.c b/sysdeps/libm-ieee754/s_csqrt.c index cda23c702d..ae106bdad8 100644 --- a/sysdeps/libm-ieee754/s_csqrt.c +++ b/sysdeps/libm-ieee754/s_csqrt.c @@ -1,5 +1,5 @@ /* Complex square root of double value. - Copyright (C) 1997 Free Software Foundation, Inc. + Copyright (C) 1997, 1998 Free Software Foundation, Inc. This file is part of the GNU C Library. Based on an algorithm by Stephen L. Moshier <moshier@world.std.com>. Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997. @@ -84,22 +84,25 @@ __csqrt (__complex__ double x) } else { -#if 0 /* FIXME: this is broken. */ - __complex__ double q; - double t, r; +#if 0 + double d, r, s; - if (fabs (__imag__ x) < 2.0e-4 * fabs (__real__ x)) - t = 0.25 * __imag__ x * (__imag__ x / __real__ x); + d = __ieee754_hypot (__real__ x, __imag__ x); + /* Use the identity 2 Re res Im res = Im x + to avoid cancellation error in d +/- Re x. */ + if (__real__ x > 0) + { + r = __ieee754_sqrt (0.5 * d + 0.5 * __real__ x); + s = (0.5 * __imag__ x) / r; + } else - t = 0.5 * (__ieee754_hypot (__real__ x, __imag__ x) - __real__ x); - - r = __ieee754_sqrt (t); - - __real__ q = __imag__ x / (2.0 * r); - __imag__ q = r; + { + s = __ieee754_sqrt (0.5 * d - 0.5 * __real__ x); + r = (0.5 * __imag__ x) / s; + } - /* Heron iteration in complex arithmetic. */ - res = 0.5 * (q + q / x); + __real__ res = r; + __imag__ res = __copysign (s, __imag__ x); #else double d, imag; |