* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
- * $Id: bitmatch.mli,v 1.20 2008-05-08 21:28:28 rjones Exp $
+ * $Id$
*)
(**
The general form of [bitmatch] is:
- [bitmatch {] {i bitstring-expression} [} with]
+ [bitmatch] {i bitstring-expression} [with]
[| {] {i pattern} [} ->] {i code}
A bitstring field of length 0 matches an empty bitstring
(occasionally useful when matching optional subfields).
- Qualifiers are a list of identifiers which control the type,
+ Qualifiers are a list of identifiers/expressions which control the type,
signedness and endianness of the field. Permissible qualifiers are:
- - [int] (field has an integer type)
- - [string] (field is a string type)
- - [bitstring] (field is a bitstring type)
- - [signed] (field is signed)
- - [unsigned] (field is unsigned)
- - [bigendian] (field is big endian - a.k.a network byte order)
- - [littleendian] (field is little endian - a.k.a Intel byte order)
- - [nativeendian] (field is same endianness as the machine)
-
- The default settings are [int], [unsigned], [bigendian].
+ - [int]: field has an integer type
+ - [string]: field is a string type
+ - [bitstring]: field is a bitstring type
+ - [signed]: field is signed
+ - [unsigned]: field is unsigned
+ - [bigendian]: field is big endian - a.k.a network byte order
+ - [littleendian]: field is little endian - a.k.a Intel byte order
+ - [nativeendian]: field is same endianness as the machine
+ - [endian (expr)]: [expr] should be an expression which evaluates to
+ a {!endian} type, ie. [LittleEndian], [BigEndian] or [NativeEndian].
+ The expression is an arbitrary OCaml expression and can use the
+ value of earlier fields in the bitmatch.
+ - [offset (expr)]: see {{:#computedoffsets}computed offsets} below.
+
+ The default settings are [int], [unsigned], [bigendian], no offset.
Note that many of these qualifiers cannot be used together,
eg. bitstrings do not have endianness. The syntax extension should
length expression in the field is a compile-time constant or a
computed expression.
- Detection of compile-time constants is quite simplistic so only an
+ Detection of compile-time constants is quite simplistic so only
simple integer literals and simple expressions (eg. [5*8]) are
recognized as constants.
still need to be a runtime check to enforce the
size).
+ {2:computedoffsets Computed offsets}
+
+ You can add an [offset(..)] qualifier to bitmatch patterns in order
+ to move the current offset within the bitstring forwards.
+
+ For example:
+
+{[
+bitmatch bits with
+| { field1 : 8;
+ field2 : 8 : offset(160) } -> ...
+]}
+
+ matches [field1] at the start of the bitstring and [field2]
+ at 160 bits into the bitstring. The middle 152 bits go
+ unmatched (ie. can be anything).
+
+ The generated code is efficient. If field lengths and offsets
+ are known to be constant at compile time, then almost all
+ runtime checks are avoided. Non-constant field lengths and/or
+ non-constant offsets can result in more runtime checks being added.
+
+ Note that moving the offset backwards, and moving the offset in
+ [BITSTRING] constructors, are both not supported at present.
+
+ {2 Named patterns and persistent patterns}
+
+ Please see {!Bitmatch_persistent} for documentation on this subject.
+
{2 Compiling}
Using the compiler directly you can do:
{v
ocamlc -I +bitmatch \
- -pp "camlp4o `ocamlc -where`/bitmatch/pa_bitmatch.cmo" \
- bitmatch.cma test.ml -o test
+ -pp "camlp4of bitmatch.cma bitmatch_persistent.cma \
+ `ocamlc -where`/bitmatch/pa_bitmatch.cmo" \
+ unix.cma bitmatch.cma test.ml -o test
v}
Simpler method using findlib:
{v
ocamlfind ocamlc \
- -package bitmatch.syntax -syntax bitmatch.syntax \
+ -package bitmatch,bitmatch.syntax -syntax bitmatch.syntax \
-linkpkg test.ml -o test
v}
let len = read_untrusted_source () in
let buffer = allocate_bitstring () in
BITSTRING {
- buffer : len : bitstring
+ buffer : len : bitstring
}
]}
For example, [make_bitstring 16 '\x5a'] will create
the bitstring [0x5a5a] or in binary [0101 1010 0101 1010].
- Note that the length is in bits, not bytes. *)
+ Note that the length is in bits, not bytes. The length does NOT
+ need to be a multiple of 8. *)
+
+val zeroes_bitstring : int -> bitstring
+(** [zeroes_bitstring] creates an [n] bit bitstring of all 0's.
+
+ Actually this is the same as {!create_bitstring}. *)
+
+val ones_bitstring : int -> bitstring
+(** [ones_bitstring] creates an [n] bit bitstring of all 1's. *)
val bitstring_of_string : string -> bitstring
(** [bitstring_of_string str] creates a bitstring
val extract_int_ne_unsigned : string -> int -> int -> int -> int * int * int
+val extract_int_ee_unsigned : endian -> string -> int -> int -> int -> int * int * int
+
val extract_int32_be_unsigned : string -> int -> int -> int -> int32 * int * int
val extract_int32_le_unsigned : string -> int -> int -> int -> int32 * int * int
val extract_int32_ne_unsigned : string -> int -> int -> int -> int32 * int * int
+val extract_int32_ee_unsigned : endian -> string -> int -> int -> int -> int32 * int * int
+
val extract_int64_be_unsigned : string -> int -> int -> int -> int64 * int * int
val extract_int64_le_unsigned : string -> int -> int -> int -> int64 * int * int
val extract_int64_ne_unsigned : string -> int -> int -> int -> int64 * int * int
+val extract_int64_ee_unsigned : endian -> string -> int -> int -> int -> int64 * int * int
+
val construct_bit : Buffer.t -> bool -> int -> exn -> unit
val construct_char_unsigned : Buffer.t -> int -> int -> exn -> unit
val construct_int_ne_unsigned : Buffer.t -> int -> int -> exn -> unit
+val construct_int_ee_unsigned : endian -> Buffer.t -> int -> int -> exn -> unit
+
val construct_int32_be_unsigned : Buffer.t -> int32 -> int -> exn -> unit
val construct_int32_ne_unsigned : Buffer.t -> int32 -> int -> exn -> unit
+val construct_int32_ee_unsigned : endian -> Buffer.t -> int32 -> int -> exn -> unit
+
val construct_int64_be_unsigned : Buffer.t -> int64 -> int -> exn -> unit
val construct_int64_ne_unsigned : Buffer.t -> int64 -> int -> exn -> unit
+val construct_int64_ee_unsigned : endian -> Buffer.t -> int64 -> int -> exn -> unit
+
val construct_string : Buffer.t -> string -> unit
+
+val construct_bitstring : Buffer.t -> bitstring -> unit