scm_bits_t / scm_ubits_t

[Dirk Herrmann]

Hello everybody,

due to a recent change, we have a scm_ubits_t type in guile, that is meant
to represent an unsigned form of scm_bits_t.  IMO, this is not a good
idea:  We should rather guarantee, that scm_bits_t itself is already an
unsigned value.  The name scm_bits_t indicates that we are dealing with
bits, i. e. a raw representation of a value.  There are places in guile
that depend on scm_bits_t being signed, but we should rather fix these
instead of introducing another type.

Further, scm_bits_t and scm_ubits_t are now used at a couple of places as
a sort-of replacement of long and unsigned long.  I'd like to clarify the
purpose of scm_bits_t:  We have introduced scm_bits_t as a type that is
used to access the bit structure of a SCM value, since SCM is a totally
opaque type.  That is, scm_bits_t is the result type of SCM_UNPACK, which
converts a SCM value to its raw bit representation.  Further, scm_bits_t
is the input type of SCM_PACK which is used to convert a scm_bits_t value
that is the raw bit representation of a scheme value to a SCM value.  And,
scm_bits_t is used to store C data in memory cells.  For the sake of
cleanliness, other uses of scm_bits_t should be avoided.

Best regards,
Dirk Herrmann