diff options
Diffstat (limited to 'libquadmath/math/cacoshq.c')
| -rw-r--r-- | libquadmath/math/cacoshq.c | 16 |
1 files changed, 11 insertions, 5 deletions
diff --git a/libquadmath/math/cacoshq.c b/libquadmath/math/cacoshq.c index 8acc570de76..263e03d0c11 100644 --- a/libquadmath/math/cacoshq.c +++ b/libquadmath/math/cacoshq.c @@ -63,6 +63,16 @@ cacoshq (__complex128 x) __real__ res = 0.0; __imag__ res = copysignq (M_PI_2q, __imag__ x); } + /* The factor 16 is just a guess. */ + else if (16.0Q * fabsq (__imag__ x) < fabsq (__real__ x)) + { + /* Kahan's formula which avoid cancellation through subtraction in + some cases. */ + res = 2.0Q * clogq (csqrtq ((x + 1.0Q) / 2.0Q) + + csqrtq ((x - 1.0Q) / 2.0Q)); + if (signbit (__real__ res)) + __real__ res = 0.0Q; + } else { __complex128 y; @@ -72,17 +82,13 @@ cacoshq (__complex128 x) y = csqrtq (y); - if (__real__ x < 0.0) + if (signbitq (x)) y = -y; __real__ y += __real__ x; __imag__ y += __imag__ x; res = clogq (y); - - /* We have to use the positive branch. */ - if (__real__ res < 0.0) - res = -res; } return res; |