1 (** Bitmatch library. *)
2 (* Copyright (C) 2008 Red Hat Inc., Richard W.M. Jones
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version,
8 * with the OCaml linking exception described in COPYING.LIB.
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Lesser General Public License for more details.
15 * You should have received a copy of the GNU Lesser General Public
16 * License along with this library; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 {{:#reference}Jump straight to the reference section for
24 documentation on types and functions}.
28 Bitmatch adds Erlang-style bitstrings and matching over bitstrings
29 as a syntax extension and library for OCaml. You can use
30 this module to both parse and generate binary formats, for
31 example, communications protocols, disk formats and binary files.
33 {{:http://code.google.com/p/bitmatch/}OCaml bitmatch website}
37 A function which can parse IPv4 packets:
44 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
45 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
46 | 4 | IHL |Type of Service| Total Length |
47 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
48 | Identification |Flags| Fragment Offset |
49 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
50 | Time to Live | Protocol | Header Checksum |
51 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
53 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
54 | Destination Address |
55 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
57 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
59 | { 4 : 4; hdrlen : 4; tos : 8; length : 16;
60 identification : 16; flags : 3; fragoffset : 13;
61 ttl : 8; protocol : 8; checksum : 16;
64 options : (hdrlen-5)*32 : bitstring;
65 payload : -1 : bitstring } ->
68 printf " header length: %d * 32 bit words\n" hdrlen;
69 printf " type of service: %d\n" tos;
70 printf " packet length: %d bytes\n" length;
71 printf " identification: %d\n" identification;
72 printf " flags: %d\n" flags;
73 printf " fragment offset: %d\n" fragoffset;
74 printf " ttl: %d\n" ttl;
75 printf " protocol: %d\n" protocol;
76 printf " checksum: %d\n" checksum;
77 printf " source: %lx dest: %lx\n" source dest;
78 printf " header options + padding:\n";
79 Bitmatch.hexdump_bitstring stdout options;
80 printf " packet payload:\n";
81 Bitmatch.hexdump_bitstring stdout payload
84 eprintf "unknown IP version %d\n" version;
88 eprintf "data is smaller than one nibble:\n";
89 Bitmatch.hexdump_bitstring stderr pkt;
93 A program which can parse
94 {{:http://lxr.linux.no/linux/include/linux/ext3_fs.h}Linux EXT3 filesystem superblocks}:
97 let bits = Bitmatch.bitstring_of_file "tests/ext3_sb"
101 | { s_inodes_count : 32 : littleendian; (* Inodes count *)
102 s_blocks_count : 32 : littleendian; (* Blocks count *)
103 s_r_blocks_count : 32 : littleendian; (* Reserved blocks count *)
104 s_free_blocks_count : 32 : littleendian; (* Free blocks count *)
105 s_free_inodes_count : 32 : littleendian; (* Free inodes count *)
106 s_first_data_block : 32 : littleendian; (* First Data Block *)
107 s_log_block_size : 32 : littleendian; (* Block size *)
108 s_log_frag_size : 32 : littleendian; (* Fragment size *)
109 s_blocks_per_group : 32 : littleendian; (* # Blocks per group *)
110 s_frags_per_group : 32 : littleendian; (* # Fragments per group *)
111 s_inodes_per_group : 32 : littleendian; (* # Inodes per group *)
112 s_mtime : 32 : littleendian; (* Mount time *)
113 s_wtime : 32 : littleendian; (* Write time *)
114 s_mnt_count : 16 : littleendian; (* Mount count *)
115 s_max_mnt_count : 16 : littleendian; (* Maximal mount count *)
116 0xef53 : 16 : littleendian } -> (* Magic signature *)
118 printf "ext3 superblock:\n";
119 printf " s_inodes_count = %ld\n" s_inodes_count;
120 printf " s_blocks_count = %ld\n" s_blocks_count;
121 printf " s_free_inodes_count = %ld\n" s_free_inodes_count;
122 printf " s_free_blocks_count = %ld\n" s_free_blocks_count
125 eprintf "not an ext3 superblock!\n%!";
129 Constructing packets for a simple binary message
134 +---------------+---------------+--------------------------+
135 | type | subtype | parameter |
136 +---------------+---------------+--------------------------+
137 <-- 16 bits --> <-- 16 bits --> <------- 32 bits -------->
139 All fields are in network byte order.
142 let make_message typ subtype param =
150 {2 Loading, creating bitstrings}
152 The basic data type is the {!bitstring}, a string of bits of
153 arbitrary length. Bitstrings can be any length in bits and
154 operations do not need to be byte-aligned (although they will
155 generally be more efficient if they are byte-aligned).
157 Internally a bitstring is stored as a normal OCaml [string]
158 together with an offset and length, where the offset and length are
159 measured in bits. Thus one can efficiently form substrings of
160 bitstrings, overlay a bitstring on existing data, and load and save
161 bitstrings from files or other external sources.
163 To load a bitstring from a file use {!bitstring_of_file} or
164 {!bitstring_of_chan}.
166 There are also functions to create bitstrings from arbitrary data.
167 See the {{:#reference}reference} below.
169 {2 Matching bitstrings with patterns}
171 Use the [bitmatch] operator (part of the syntax extension) to break
172 apart a bitstring into its fields. [bitmatch] works a lot like the
173 OCaml [match] operator.
175 The general form of [bitmatch] is:
177 [bitmatch] {i bitstring-expression} [with]
179 [| {] {i pattern} [} ->] {i code}
181 [| {] {i pattern} [} ->] {i code}
185 As with normal match, the statement attempts to match the
186 bitstring against each pattern in turn. If none of the patterns
187 match then the standard library [Match_failure] exception is
190 Patterns look a bit different from normal match patterns. They
191 consist of a list of bitfields separated by [;] where each bitfield
192 contains a bind variable, the width (in bits) of the field, and
193 other information. Some example patterns:
198 | { version : 8; name : 8; param : 8 } -> ...
200 (* Bitstring of at least 3 bytes. First byte is the version
201 number, second byte is a field called name, third byte is
202 a field called parameter. *)
205 printf "flag is %b\n" flag
207 (* A single flag bit (mapped into an OCaml boolean). *)
209 | { len : 4; data : 1+len } ->
210 printf "len = %d, data = 0x%Lx\n" len data
212 (* A 4-bit length, followed by 1-16 bits of data, where the
213 length of the data is computed from len. *)
215 | { ipv6_source : 128 : bitstring;
216 ipv6_dest : 128 : bitstring } -> ...
218 (* IPv6 source and destination addresses. Each is 128 bits
219 and is mapped into a bitstring type which will be a substring
220 of the main bitstring expression. *)
223 You can also add conditional when-clauses:
227 when version = 4 || version = 6 -> ...
229 (* Only match and run the code when version is 4 or 6. If
230 it isn't we will drop through to the next case. *)
233 Note that the pattern is only compared against the first part of
234 the bitstring (there may be more data in the bitstring following
235 the pattern, which is not matched). In terms of regular
236 expressions you might say that the pattern matches [^pattern], not
237 [^pattern$]. To ensure that the bitstring contains only the
238 pattern, add a length -1 bitstring to the end and test that its
239 length is zero in the when-clause:
243 rest : -1 : bitstring }
244 when Bitmatch.bitstring_length rest = 0 -> ...
246 (* Only matches exactly 4 bits. *)
249 Normally the first part of each field is a binding variable,
250 but you can also match a constant, as in:
253 | { (4|6) : 4 } -> ...
255 (* Only matches if the first 4 bits contain either
256 the integer 4 or the integer 6. *)
259 One may also match on strings:
262 | { "MAGIC" : 5*8 : string } -> ...
264 (* Only matches if the string "MAGIC" appears at the start
268 {3:patternfieldreference Pattern field reference}
270 The exact format of each pattern field is:
272 [pattern : length [: qualifier [,qualifier ...]]]
274 [pattern] is the pattern, binding variable name, or constant to
275 match. [length] is the length in bits which may be either a
276 constant or an expression. The length expression is just an OCaml
277 expression and can use any values defined in the program, and refer
278 back to earlier fields (but not to later fields).
280 Integers can only have lengths in the range \[1..64\] bits. See the
281 {{:#integertypes}integer types} section below for how these are
282 mapped to the OCaml int/int32/int64 types. This is checked
283 at compile time if the length expression is constant, otherwise it is
284 checked at runtime and you will get a runtime exception eg. in
285 the case of a computed length expression.
287 A bitstring field of length -1 matches all the rest of the
288 bitstring (thus this is only useful as the last field in a
291 A bitstring field of length 0 matches an empty bitstring
292 (occasionally useful when matching optional subfields).
294 Qualifiers are a list of identifiers/expressions which control the type,
295 signedness and endianness of the field. Permissible qualifiers are:
297 - [int]: field has an integer type
298 - [string]: field is a string type
299 - [bitstring]: field is a bitstring type
300 - [signed]: field is signed
301 - [unsigned]: field is unsigned
302 - [bigendian]: field is big endian - a.k.a network byte order
303 - [littleendian]: field is little endian - a.k.a Intel byte order
304 - [nativeendian]: field is same endianness as the machine
305 - [endian (expr)]: [expr] should be an expression which evaluates to
306 a {!endian} type, ie. [LittleEndian], [BigEndian] or [NativeEndian].
307 The expression is an arbitrary OCaml expression and can use the
308 value of earlier fields in the bitmatch.
309 - [offset (expr)]: see {{:#computedoffsets}computed offsets} below.
311 The default settings are [int], [unsigned], [bigendian], no offset.
313 Note that many of these qualifiers cannot be used together,
314 eg. bitstrings do not have endianness. The syntax extension should
315 give you a compile-time error if you use incompatible qualifiers.
317 {3 Other cases in bitmatch}
319 As well as a list of fields, it is possible to name the
320 bitstring and/or have a default match case:
325 (* Default match case. *)
327 | { _ } as pkt -> ...
329 (* Default match case, with 'pkt' bound to the whole bitstring. *)
332 {2 Constructing bitstrings}
334 Bitstrings may be constructed using the [BITSTRING] operator (as an
335 expression). The [BITSTRING] operator takes a list of fields,
336 similar to the list of fields for matching:
347 (* Constructs a 16-bit bitstring with the first four bits containing
348 the integer 1, and the following 12 bits containing the integer 10,
349 arranged in network byte order. *)
351 Bitmatch.hexdump_bitstring stdout bits ;;
359 The format of each field is the same as for pattern fields (see
360 {{:#patternfieldreference}Pattern field reference section}), and
361 things like computed length fields, fixed value fields, insertion
362 of bitstrings within bitstrings, etc. are all supported.
364 {3 Construction exception}
366 The [BITSTRING] operator may throw a {!Construct_failure}
367 exception at runtime.
369 Runtime errors include:
371 - int field length not in the range \[1..64\]
372 - a bitstring with a length declared which doesn't have the
373 same length at runtime
374 - trying to insert an out of range value into an int field
375 (eg. an unsigned int field which is 2 bits wide can only
376 take values in the range \[0..3\]).
378 {2:integertypes Integer types}
380 Integer types are mapped to OCaml types [bool], [int], [int32] or
381 [int64] using a system which tries to ensure that (a) the types are
382 reasonably predictable and (b) the most efficient type is
385 The rules are slightly different depending on whether the bit
386 length expression in the field is a compile-time constant or a
389 Detection of compile-time constants is quite simplistic so only
390 simple integer literals and simple expressions (eg. [5*8]) are
391 recognized as constants.
393 In any case the bit size of an integer is limited to the range
394 \[1..64\]. This is detected as a compile-time error if that is
395 possible, otherwise a runtime check is added which can throw an
396 [Invalid_argument] exception.
401 Bit size ---- OCaml type ----
402 Constant Computed expression
410 A possible future extension may allow people with 64 bit computers
411 to specify a more optimal [int] type for bit sizes in the range
412 [32..63]. If this was implemented then such code {i could not even
413 be compiled} on 32 bit platforms, so it would limit portability.
415 Another future extension may be to allow computed
416 expressions to assert min/max range for the bit size,
417 allowing a more efficient data type than int64 to be
418 used. (Of course under such circumstances there would
419 still need to be a runtime check to enforce the
422 {2 Advanced pattern-matching features}
424 {3:computedoffsets Computed offsets}
426 You can add an [offset(..)] qualifier to bitmatch patterns in order
427 to move the current offset within the bitstring forwards.
434 field2 : 8 : offset(160) } -> ...
437 matches [field1] at the start of the bitstring and [field2]
438 at 160 bits into the bitstring. The middle 152 bits go
439 unmatched (ie. can be anything).
441 The generated code is efficient. If field lengths and offsets
442 are known to be constant at compile time, then almost all
443 runtime checks are avoided. Non-constant field lengths and/or
444 non-constant offsets can result in more runtime checks being added.
446 Note that moving the offset backwards, and moving the offset in
447 [BITSTRING] constructors, are both not supported at present.
449 {3 Check expressions}
451 You can add a [check(expr)] qualifier to bitmatch patterns.
452 If the expression evaluates to false then the current match case
453 fails to match (in other words, we fall through to the next
454 match case - there is no error).
459 | { field : 16 : check (field > 100) } -> ...
462 Note the difference between a check expression and a when-clause
463 is that the when-clause is evaluated after all the fields have
464 been matched. On the other hand a check expression is evaluated
465 after the individual field has been matched, which means it is
466 potentially more efficient (if the check expression fails then
467 we don't waste any time matching later fields).
469 We wanted to use the notation [when(expr)] here, but because
470 [when] is a reserved word we could not do this.
474 A bind expression is used to change the value of a matched
478 | { len : 16 : bind (len * 8);
479 field : len : bitstring } -> ...
482 In the example, after 'len' has been matched, its value would
483 be multiplied by 8, so the width of 'field' is the matched
484 value multiplied by 8.
488 | { field : ... : bind (expr) } -> ...
490 evaluates the following after the field has been matched:
493 (* remaining fields *)
496 {3 Order of evaluation of check() and bind()}
498 The choice is arbitrary, but we have chosen that check expressions
499 are evaluated first, and bind expressions are evaluated after.
501 This means that the result of bind() is {i not} available in
502 the check expression.
504 Note that this rule applies regardless of the order of check()
505 and bind() in the source code.
509 Use [save_offset_to(variable)] to save the current bit offset
510 within the match to a variable (strictly speaking, to a pattern).
511 This variable is then made available in any [check()] and [bind()]
512 clauses in the current field, {i and} to any later fields, and
513 to the code after the [->].
520 field : 16 : save_offset_to (field_offset) } ->
521 printf "field is at bit offset %d in the match\n" field_offset
524 (In that example, [field_offset] should always have the value
527 {2 Named patterns and persistent patterns}
529 Please see {!Bitmatch_persistent} for documentation on this subject.
533 Using the compiler directly you can do:
536 ocamlc -I +bitmatch \
537 -pp "camlp4of bitmatch.cma bitmatch_persistent.cma \
538 `ocamlc -where`/bitmatch/pa_bitmatch.cmo" \
539 unix.cma bitmatch.cma test.ml -o test
542 Simpler method using findlib:
546 -package bitmatch,bitmatch.syntax -syntax bitmatch.syntax \
547 -linkpkg test.ml -o test
550 {2 Security and type safety}
552 {3 Security on input}
554 The main concerns for input are buffer overflows and denial
557 It is believed that this library is robust against attempted buffer
558 overflows. In addition to OCaml's normal bounds checks, we check
559 that field lengths are >= 0, and many additional checks.
561 Denial of service attacks are more problematic. We only work
562 forwards through the bitstring, thus computation will eventually
563 terminate. As for computed lengths, code such as this is thought
569 buffer : Int64.to_int len : bitstring } ->
572 The [len] field can be set arbitrarily large by an attacker, but
573 when pattern-matching against the [buffer] field this merely causes
574 a test such as [if len <= remaining_size] to fail. Even if the
575 length is chosen so that [buffer] bitstring is allocated, the
576 allocation of sub-bitstrings is efficient and doesn't involve an
577 arbitary-sized allocation or any copying.
579 However the above does not necessarily apply to strings used in
580 matching, since they may cause the library to use the
581 {!Bitmatch.string_of_bitstring} function, which allocates a string.
582 So you should take care if you use the [string] type particularly
583 with a computed length that is derived from external input.
585 The main protection against attackers should be to ensure that the
586 main program will only read input bitstrings up to a certain
587 length, which is outside the scope of this library.
589 {3 Security on output}
591 As with the input side, computed lengths are believed to be
595 let len = read_untrusted_source () in
596 let buffer = allocate_bitstring () in
598 buffer : len : bitstring
602 This code merely causes a check that buffer's length is the same as
603 [len]. However the program function [allocate_bitstring] must
604 refuse to allocate an oversized buffer (but that is outside the
605 scope of this library).
607 {3 Order of evaluation}
609 In [bitmatch] statements, fields are evaluated left to right.
611 Note that the when-clause is evaluated {i last}, so if you are
612 relying on the when-clause to filter cases then your code may do a
613 lot of extra and unncessary pattern-matching work on fields which
614 may never be needed just to evaluate the when-clause. You can
615 usually rearrange the code to do only the first part of the match,
616 followed by the when-clause, followed by a second inner bitmatch.
620 The current implementation is believed to be fully type-safe,
621 and makes compile and run-time checks where appropriate. If
622 you find a case where a check is missing please submit a
623 bug report or a patch.
627 These are thought to be the current limits:
629 Integers: \[1..64\] bits.
631 Bitstrings (32 bit platforms): maximum length is limited
632 by the string size, ie. 16 MBytes.
634 Bitstrings (64 bit platforms): maximum length is thought to be
635 limited by the string size, ie. effectively unlimited.
637 Bitstrings must be loaded into memory before we can match against
638 them. Thus available memory may be considered a limit for some
641 {2:reference Reference}
645 type endian = BigEndian | LittleEndian | NativeEndian
647 val string_of_endian : endian -> string
650 type bitstring = string * int * int
651 (** [bitstring] is the basic type used to store bitstrings.
653 The type contains the underlying data (a string),
654 the current bit offset within the string and the
655 current bit length of the string (counting from the
656 bit offset). Note that the offset and length are
657 in {b bits}, not bytes.
659 Normally you don't need to use the bitstring type
660 directly, since there are functions and syntax
661 extensions which hide the details.
663 See also {!bitstring_of_string}, {!bitstring_of_file},
664 {!hexdump_bitstring}, {!bitstring_length}.
667 (** {3 Exceptions} *)
669 exception Construct_failure of string * string * int * int
670 (** [Construct_failure (message, file, line, char)] may be
671 raised by the [BITSTRING] constructor.
673 Common reasons are that values are out of range of
674 the fields that contain them, or that computed lengths
675 are impossible (eg. negative length bitfields).
677 [message] is the error message.
679 [file], [line] and [char] point to the original source
680 location of the [BITSTRING] constructor that failed.
683 (** {3 Bitstring manipulation} *)
685 val bitstring_length : bitstring -> int
686 (** [bitstring_length bitstring] returns the length of
687 the bitstring in bits.
689 Note this just returns the third field in the {!bitstring} tuple. *)
691 val subbitstring : bitstring -> int -> int -> bitstring
692 (** [subbitstring bits off len] returns a sub-bitstring
693 of the bitstring, starting at offset [off] bits and
694 with length [len] bits.
696 If the original bitstring is not long enough to do this
697 then the function raises [Invalid_argument "subbitstring"].
699 Note that this function just changes the offset and length
700 fields of the {!bitstring} tuple, so is very efficient. *)
702 val dropbits : int -> bitstring -> bitstring
703 (** Drop the first n bits of the bitstring and return a new
704 bitstring which is shorter by n bits.
706 If the length of the original bitstring is less than n bits,
707 this raises [Invalid_argument "dropbits"].
709 Note that this function just changes the offset and length
710 fields of the {!bitstring} tuple, so is very efficient. *)
712 val takebits : int -> bitstring -> bitstring
713 (** Take the first n bits of the bitstring and return a new
714 bitstring which is exactly n bits long.
716 If the length of the original bitstring is less than n bits,
717 this raises [Invalid_argument "takebits"].
719 Note that this function just changes the offset and length
720 fields of the {!bitstring} tuple, so is very efficient. *)
722 (** {3 Constructing bitstrings} *)
724 val empty_bitstring : bitstring
725 (** [empty_bitstring] is the empty, zero-length bitstring. *)
727 val create_bitstring : int -> bitstring
728 (** [create_bitstring n] creates an [n] bit bitstring
729 containing all zeroes. *)
731 val make_bitstring : int -> char -> bitstring
732 (** [make_bitstring n c] creates an [n] bit bitstring
733 containing the repeated 8 bit pattern in [c].
735 For example, [make_bitstring 16 '\x5a'] will create
736 the bitstring [0x5a5a] or in binary [0101 1010 0101 1010].
738 Note that the length is in bits, not bytes. The length does NOT
739 need to be a multiple of 8. *)
741 val zeroes_bitstring : int -> bitstring
742 (** [zeroes_bitstring] creates an [n] bit bitstring of all 0's.
744 Actually this is the same as {!create_bitstring}. *)
746 val ones_bitstring : int -> bitstring
747 (** [ones_bitstring] creates an [n] bit bitstring of all 1's. *)
749 val bitstring_of_string : string -> bitstring
750 (** [bitstring_of_string str] creates a bitstring
751 of length [String.length str * 8] (bits) containing the
754 Note that the bitstring uses [str] as the underlying
755 string (see the representation of {!bitstring}) so you
756 should not change [str] after calling this. *)
758 val bitstring_of_file : string -> bitstring
759 (** [bitstring_of_file filename] loads the named file
762 val bitstring_of_chan : in_channel -> bitstring
763 (** [bitstring_of_chan chan] loads the contents of
764 the input channel [chan] as a bitstring.
766 The length of the final bitstring is determined
767 by the remaining input in [chan], but will always
768 be a multiple of 8 bits.
770 See also {!bitstring_of_chan_max}. *)
772 val bitstring_of_chan_max : in_channel -> int -> bitstring
773 (** [bitstring_of_chan_max chan max] works like
774 {!bitstring_of_chan} but will only read up to
775 [max] bytes from the channel (or fewer if the end of input
776 occurs before that). *)
778 val bitstring_of_file_descr : Unix.file_descr -> bitstring
779 (** [bitstring_of_file_descr fd] loads the contents of
780 the file descriptor [fd] as a bitstring.
782 See also {!bitstring_of_chan}, {!bitstring_of_file_descr_max}. *)
784 val bitstring_of_file_descr_max : Unix.file_descr -> int -> bitstring
785 (** [bitstring_of_file_descr_max fd max] works like
786 {!bitstring_of_file_descr} but will only read up to
787 [max] bytes from the channel (or fewer if the end of input
788 occurs before that). *)
790 (** {3 Converting bitstrings} *)
792 val string_of_bitstring : bitstring -> string
793 (** [string_of_bitstring bitstring] converts a bitstring to a string
794 (eg. to allow comparison).
796 This function is inefficient. In the best case when the bitstring
797 is nicely byte-aligned we do a [String.sub] operation. If the
798 bitstring isn't aligned then this involves a lot of bit twiddling
799 and is particularly inefficient.
801 If the bitstring is not a multiple of 8 bits wide then the
802 final byte of the string contains the high bits set to the
803 remaining bits and the low bits set to 0. *)
805 val bitstring_to_file : bitstring -> string -> unit
806 (** [bitstring_to_file bits filename] writes the bitstring [bits]
807 to the file [filename]. It overwrites the output file.
809 Some restrictions apply, see {!bitstring_to_chan}. *)
811 val bitstring_to_chan : bitstring -> out_channel -> unit
812 (** [bitstring_to_file bits filename] writes the bitstring [bits]
813 to the channel [chan].
815 Channels are made up of bytes, bitstrings can be any bit length
816 including fractions of bytes. So this function only works
817 if the length of the bitstring is an exact multiple of 8 bits
818 (otherwise it raises [Invalid_argument "bitstring_to_chan"]).
820 Furthermore the function is efficient only in the case where
821 the bitstring is stored fully aligned, otherwise it has to
822 do inefficient bit twiddling like {!string_of_bitstring}.
824 In the common case where the bitstring was generated by the
825 [BITSTRING] operator and is an exact multiple of 8 bits wide,
826 then this function will always work efficiently.
829 (** {3 Printing bitstrings} *)
831 val hexdump_bitstring : out_channel -> bitstring -> unit
832 (** [hexdump_bitstring chan bitstring] prints the bitstring
833 to the output channel in a format similar to the
834 Unix command [hexdump -C]. *)
836 (** {3 Bitstring buffer} *)
840 val create : unit -> t
841 val contents : t -> bitstring
842 val add_bits : t -> string -> int -> unit
843 val add_bit : t -> bool -> unit
844 val add_byte : t -> int -> unit
846 (** Buffers are mainly used by the [BITSTRING] constructor, but
847 may also be useful for end users. They work much like the
848 standard library [Buffer] module. *)
850 (** {3 Miscellaneous} *)
853 (** The package name, always ["ocaml-bitmatch"] *)
856 (** The package version as a string. *)
859 (** Set this variable to true to enable extended debugging.
860 This only works if debugging was also enabled in the
861 [pa_bitmatch.ml] file at compile time, otherwise it
866 (* Private functions, called from generated code. Do not use
867 * these directly - they are not safe.
870 val extract_bitstring : string -> int -> int -> int -> bitstring * int * int
872 val extract_remainder : string -> int -> int -> bitstring * int * int
874 val extract_bit : string -> int -> int -> int -> bool * int * int
876 val extract_char_unsigned : string -> int -> int -> int -> int * int * int
878 val extract_int_be_unsigned : string -> int -> int -> int -> int * int * int
880 val extract_int_le_unsigned : string -> int -> int -> int -> int * int * int
882 val extract_int_ne_unsigned : string -> int -> int -> int -> int * int * int
884 val extract_int_ee_unsigned : endian -> string -> int -> int -> int -> int * int * int
886 val extract_int32_be_unsigned : string -> int -> int -> int -> int32 * int * int
888 val extract_int32_le_unsigned : string -> int -> int -> int -> int32 * int * int
890 val extract_int32_ne_unsigned : string -> int -> int -> int -> int32 * int * int
892 val extract_int32_ee_unsigned : endian -> string -> int -> int -> int -> int32 * int * int
894 val extract_int64_be_unsigned : string -> int -> int -> int -> int64 * int * int
896 val extract_int64_le_unsigned : string -> int -> int -> int -> int64 * int * int
898 val extract_int64_ne_unsigned : string -> int -> int -> int -> int64 * int * int
900 val extract_int64_ee_unsigned : endian -> string -> int -> int -> int -> int64 * int * int
902 val construct_bit : Buffer.t -> bool -> int -> exn -> unit
904 val construct_char_unsigned : Buffer.t -> int -> int -> exn -> unit
906 val construct_int_be_unsigned : Buffer.t -> int -> int -> exn -> unit
908 val construct_int_ne_unsigned : Buffer.t -> int -> int -> exn -> unit
910 val construct_int_ee_unsigned : endian -> Buffer.t -> int -> int -> exn -> unit
912 val construct_int32_be_unsigned : Buffer.t -> int32 -> int -> exn -> unit
914 val construct_int32_ne_unsigned : Buffer.t -> int32 -> int -> exn -> unit
916 val construct_int32_ee_unsigned : endian -> Buffer.t -> int32 -> int -> exn -> unit
918 val construct_int64_be_unsigned : Buffer.t -> int64 -> int -> exn -> unit
920 val construct_int64_ne_unsigned : Buffer.t -> int64 -> int -> exn -> unit
922 val construct_int64_ee_unsigned : endian -> Buffer.t -> int64 -> int -> exn -> unit
924 val construct_string : Buffer.t -> string -> unit
926 val construct_bitstring : Buffer.t -> bitstring -> unit