sail_sv_backend: swap element ordering for unpacked array

In SystemVerilog, unpacked arrays are typically in the form of
`[0:LEN-1]` instead of `[LEN-1:0]` (which is the convention for packed
arrays). In fact, commonly people just use `[LEN]` and this is a
shorthand for `[0:LEN-1]`.

Currently sail_sv_backend always use `[LEN-1:0]` even for unpacked
arrays; this causes the whole array to be flipped even the user passed
in an array declared with `[LEN]`.

Author: nbdd0121

src/sail_sv_backend/jib_sv.ml

@@ -162,7 +162,7 @@ module Make (Config : CONFIG) = struct
         ksprintf simple_type "logic [%d:0]" (width - 1)
     | CT_ref ctyp -> ksprintf simple_type "sail_reg_%s" (Util.zencode_string (string_of_ctyp ctyp))
     | CT_fvector (len, ctyp) ->
-        let outer_index = sprintf "[%d:0]" (len - 1) in
+        let outer_index = sprintf "[%d]" len in
         begin
           match sv_ctyp ctyp with
           | ty, Some inner_index -> (ty, Some (inner_index ^ outer_index))

src/sail_sv_backend/sail_plugin_sv.ml

@@ -469,7 +469,7 @@ let verilog_target _ default_sail_dir out_opt ast effect_info env =
           ) ^^ hardline ^^ string "end" ^^ hardline
         in
         let fun_body = concat (List.init slots fun_body_slot) ^^ string "sail_reached_unreachable = 1;" in
-        let slot_ranges = string ("[" ^ string_of_int (slots - 1) ^ ":0]") in
+        let slot_ranges = string ("[" ^ string_of_int slots ^ "]") in
         ( sv_fundef_with ctx real_name arg_nms arg_typs ret_ty fun_body ^^ twice hardline,
           separate space [string "output"; string "bit"; invoke_flag ^^ slot_ranges]
           :: separate space [string "input"; string (fst (sv_ctyp ret_ty)); result ^^ slot_ranges]