c99 number funcs

[Kevin Ryde]

This is a small change to make use of c99 math functions when
available, for instance in recent glibc.

There shouldn't be much difference, though there's probably a good
chance of getting higher accuracy or range from the library asinh etc
than from an equivalent expression.

Removing the private isfinite is a good thing on its own, don't want
to have problems on a c99 system.

        * configure.in (AC_CHECK_FUNCS): Add asinh, acosh, atanh, round, trunc.

        * numbers.c (_GNU_SOURCE): #define, to get C99 things.
        (scm_asinh, scm_acosh, scm_atanh, scm_truncate, scm_round, $asinh,
        $acosh, $atanh, truncate, round): Use C library asinh, acosh, atanh,
        trunc and round, when available.
        (scm_inexact_to_exact): Expand isfinite to its definition !isinf.
        (isfinite): Remove, conflicts with C99 isfinite().

        * tests/numbers.test (trunc, round, asinh, acosh, atanh): Add some
        tests.

configure.in.c99.diff
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numbers.c.c99.diff
Description: Text document

numbers.test.c99.diff
Description: Text document