angle and scm_flo0

[Kevin Ryde]

To save a bit of consing and calls to atan2,

        * numbers.c (scm_angle): Use scm_flo0 for non-negative inum, bignum
        and real.

I guess the same can be done for negatives, returning pi.  Would
scm_sys_protects be the right place to add an scm_flo_pi?  I see
abs_most_negative_fixnum uses scm_permanent_object instead.

For the actual pi value, I guess there'd be a choice between M_PI and
the return from atan2(0.0,-1.0).  The two ought to be the same of
course.  Maybe use the constant and have one of the tests see that
atan2 agrees.

numbers.c.angle-flo0.diff
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angle.test
Description: Text document