erroneous NaN from tanh if complex argument

[danny.johnson.vmail at verizon.net]

--------
Bug report for Octave 2.9.16 configured for i686-pc-msdosmsvc

Description:
-----------

Octave erroneously declares NaN when encountering exponent underflow in tanh with argument having high real absolute value and any reasonable complex part (answer should simply be +/- 1.0 real).  The size of the complex part does not matter greatly; simply being non-zero causes NaN when abs{real{argument}} > about 355.5 (i.e. when the imaginary part in the result would have an exponent underflow).

Note: the configuration data below may be confusing--I am running the Windows version from sourceforge.net but I brought up Cygwin in order to run this bug script. Running on AMD Athlon X2, Windows Vista Home Premium, 2GB RAM.

Repeat-By:
---------

octave.exe:34> tanh(355.5 + .1i)
ans = 1.0000e+000 + 6.5431e-310i

octave.exe:35> tanh(355.6 + .1i)
ans = NaN



Configuration (please do not edit this section):
-----------------------------------------------

uname output:     CYGWIN_NT-6.0 Danny-PC 1.5.24(0.156/4/2) 2007-01-31 10:57 i686 Cygwin
configure opts:   '--build=i686-pc-msdosmsvc' '--prefix=/c/Temp/vclibs_tmp/local/octave-2.9.16' '--with-zlib=zlib' 'build_alias=i686-pc-msdosmsvc' 'CC=cc-msvc' 'CFLAGS=-O2' 'CXX=cc-msvc' 'CXXFLAGS=-O2' 'F77=fc-msvc' 'FFLAGS=-O2'
Fortran compiler: fc-msvc
FFLAGS:           -O2
F2C:              @F2C@
F2CFLAGS:         @F2CFLAGS@
FLIBS:            -lhdf5 -lzlib -lf2c -lkernel32
CPPFLAGS:         -I. 
INCFLAGS:         -I. -I. -I./liboctave -I./src -I./libcruft/misc 
C compiler:       
CFLAGS:           -O2 -MD
CPICFLAG:         
C++ compiler:     
CXXFLAGS:         -O2 -EHs -MD
CXXPICFLAG:       
LD_CXX:           cc-msvc
LDFLAGS:          
LIBFLAGS:         -L.
RLD_FLAG:         
BLAS_LIBS:        -llapack -lblas
FFTW_LIBS:        -lfftw3
LIBS:             -lreadline  -lncurses -lhdf5 -lzlib  -lws2_32 -lkernel32
LEXLIB:           
LIBDLFCN:         
LIBGLOB:          -lglob
SED:              /usr/bin/sed
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