gamma(lgamma) error in libm(signgam undeclared)

[Cliff Tsai]

Hi:
    When using gamma and lgamma in libm,
    I have the error: siganam undeclared.
    And after adding following two lines(suggestion from From: "J. Johnston"
<jjohnstn at cygnus dot com>
        Date: Mon, 29 Jan 2001 18:01:30 -0500 )
    extern __IMPORT struct _reent reent_data;
    #define signgam reent_data._new._reent._gamma_signgam

    I have another problem:undefined reference to `reent_data'.

    I've seen the struct _reent is defined in sys/reent.h .
    math.h also have #include <sys/reent.h>.
    But I still can't find out what's the problem!

    Thanks for any help!