[Bug math/13629] clog() returns wrong values around z=1

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=13629

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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         AssignedTo|aj at suse dot de           |unassigned at sourceware
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--- Comment #4 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-03-03 21:26:56 UTC ---
Confirmed in current source code by inspection.  The implementation approach of
log(hypot) for finding the real part of clog will cause undue overflows for
large input, inaccurate results from undue underflow for subnormal input, and
inaccurate results for z close to |z|=1 (not just close to 1 itself).  The
general case of z close to that circle will be more complicated to fix than the
overflow and underflow cases.

clog10 (a GNU extension, name reserved in ISO C) has the same issues.

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