ffi: bitfield support.

* ffi.c (sbit_s, ubit_s): New symbol variables.
(struct txr_ffi_type): New members, shift and mask.
(ffi_sbit_put, ffi_sbit_get, ffi_ubit_put, ffi_ubit_get,
bitfield_syntax_p): New static functions.
(make_ffi_type_pointer): Disallow pointers to bitfields.
(make_ffi_type_struct): Process bitfield members and
set up shifts and masks accordingly. Recently introduced
bug fixed here at the same time: the alignment calculation
for each member must be done top-of-loop.
(ffi_struct_compile): Exclude bitfields from the check
against members with zero type. Compile the bitfield syntax.
(ffi_typedef): Do not allow typedefs of bitfield type.
Not only doesn't this make sense, but bitfield types
are destructively modified in make_ffi_type_struct: they
are imbued with a mask and offset tied to their position in
a particular struct.

* ffi.h (sbit_s, ubit_s): Delared.

* txr.1: Documented bitfields.

1 files changed, 2 insertions, 0 deletions

diff --git a/ffi.h b/ffi.h
index c6a7102a..5d89e452 100644
--- a/ffi.h
+++ b/ffi.h
@@ -51,6 +51,8 @@ extern val ptr_in_s, ptr_out_s, ptr_in_d_s, ptr_out_d_s, ptr_out_s_s, ptr_s;
 
 extern val closure_s;
 
+extern val sbit_s, ubit_s;
+
 extern val ffi_type_s, ffi_call_desc_s, ffi_closure_s;
 
 val ffi_type_compile(val syntax);