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Autoconf
========

   Autoconf based applications can easily check whether GMP is
installed.  The only thing to be noted is that GMP library symbols from
version 3 onwards have prefixes like `__gmpz'.  The following therefore
would be a simple test,

     AC_CHECK_LIB(gmp, __gmpz_init)

   This just uses the default `AC_CHECK_LIB' actions for found or not
found, but an application that must have GMP would want to generate an
error if not found.  For example,

     AC_CHECK_LIB(gmp, __gmpz_init, , [AC_MSG_ERROR(
     [GNU MP not found, see http://swox.com/gmp])])

   If functions added in some particular version of GMP are required,
then one of those can be used when checking.  For example `mpz_mul_si'
was added in GMP 3.1,

     AC_CHECK_LIB(gmp, __gmpz_mul_si, , [AC_MSG_ERROR(
     [GNU MP not found, or not 3.1 or up, see http://swox.com/gmp])])

   An alternative would be to test the version number in `gmp.h' using
say `AC_EGREP_CPP'.  That would make it possible to test the exact
version, if some particular sub-minor release is known to be necessary.

   An application that can use either GMP 2 or 3 will need to test for
`__gmpz_init' (GMP 3 and up) or `mpz_init' (GMP 2), and it's also worth
checking for `libgmp2' since Debian GNU/Linux systems used that name in
the past.  For example,

     AC_CHECK_LIB(gmp, __gmpz_init, ,
       [AC_CHECK_LIB(gmp, mpz_init, ,
         [AC_CHECK_LIB(gmp2, mpz_init)])])

   In general it's suggested that applications should simply demand a
new enough GMP rather than trying to provide supplements for features
not available in past versions.

   Occasionally an application will need or want to know the size of a
type at configuration or preprocessing time, not just with `sizeof' in
the code.  This can be done in the normal way with `mp_limb_t' etc, but
GMP 4.0 or up is best for this, since prior versions needed certain
`-D' defines on systems using a `long long' limb.  The following would
suit Autoconf 2.50 or up,

     AC_CHECK_SIZEOF(mp_limb_t, , [#include <gmp.h>])

   The optional `mpfr' functions are provided in a separate
`libmpfr.a', and this might be from GMP with `--enable-mpfr' or from
MPFR installed separately.  Either way `libmpfr' depends on `libgmp',
it doesn't stand alone.  Currently only a static `libmpfr.a' will be
available, not a shared library, since upward binary compatibility is
not guaranteed.

     AC_CHECK_LIB(mpfr, mpfr_add, , [AC_MSG_ERROR(
     [Need MPFR either from GNU MP 4 or separate MPFR package.
     See http://www.mpfr.org or http://swox.com/gmp])