* lib/math.in.h (ldexpf): New declaration.
* lib/ldexpf.c: New file.
* m4/ldexpf.m4: New file.
* m4/math_h.m4 (gl_MATH_H): Test whether ldexpf is declared.
(gl_MATH_H_DEFAULTS): Initialize GNULIB_LDEXPF, HAVE_LDEXPF.
* modules/math (Makefile.am): Substitute GNULIB_LDEXPF, HAVE_LDEXPF.
* modules/ldexpf: New file.
* tests/test-math-c++.cc: Check the declaration of ldexpf.
* doc/posix-functions/ldexpf.texi: Mention the new module.