1 (** Bitstring 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 Bitstring 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/bitstring/}OCaml bitstring website}
35 This library used to be called "bitmatch".
39 A function which can parse IPv4 packets:
46 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
47 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
48 | 4 | IHL |Type of Service| Total Length |
49 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
50 | Identification |Flags| Fragment Offset |
51 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
52 | Time to Live | Protocol | Header Checksum |
53 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
55 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
56 | Destination Address |
57 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
59 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
61 | { 4 : 4; hdrlen : 4; tos : 8; length : 16;
62 identification : 16; flags : 3; fragoffset : 13;
63 ttl : 8; protocol : 8; checksum : 16;
66 options : (hdrlen-5)*32 : bitstring;
67 payload : -1 : bitstring } ->
70 printf " header length: %d * 32 bit words\n" hdrlen;
71 printf " type of service: %d\n" tos;
72 printf " packet length: %d bytes\n" length;
73 printf " identification: %d\n" identification;
74 printf " flags: %d\n" flags;
75 printf " fragment offset: %d\n" fragoffset;
76 printf " ttl: %d\n" ttl;
77 printf " protocol: %d\n" protocol;
78 printf " checksum: %d\n" checksum;
79 printf " source: %lx dest: %lx\n" source dest;
80 printf " header options + padding:\n";
81 Bitstring.hexdump_bitstring stdout options;
82 printf " packet payload:\n";
83 Bitstring.hexdump_bitstring stdout payload
86 eprintf "unknown IP version %d\n" version;
90 eprintf "data is smaller than one nibble:\n";
91 Bitstring.hexdump_bitstring stderr pkt;
95 A program which can parse
96 {{:http://lxr.linux.no/linux/include/linux/ext3_fs.h}Linux EXT3 filesystem superblocks}:
99 let bits = Bitstring.bitstring_of_file "tests/ext3_sb"
103 | { s_inodes_count : 32 : littleendian; (* Inodes count *)
104 s_blocks_count : 32 : littleendian; (* Blocks count *)
105 s_r_blocks_count : 32 : littleendian; (* Reserved blocks count *)
106 s_free_blocks_count : 32 : littleendian; (* Free blocks count *)
107 s_free_inodes_count : 32 : littleendian; (* Free inodes count *)
108 s_first_data_block : 32 : littleendian; (* First Data Block *)
109 s_log_block_size : 32 : littleendian; (* Block size *)
110 s_log_frag_size : 32 : littleendian; (* Fragment size *)
111 s_blocks_per_group : 32 : littleendian; (* # Blocks per group *)
112 s_frags_per_group : 32 : littleendian; (* # Fragments per group *)
113 s_inodes_per_group : 32 : littleendian; (* # Inodes per group *)
114 s_mtime : 32 : littleendian; (* Mount time *)
115 s_wtime : 32 : littleendian; (* Write time *)
116 s_mnt_count : 16 : littleendian; (* Mount count *)
117 s_max_mnt_count : 16 : littleendian; (* Maximal mount count *)
118 0xef53 : 16 : littleendian } -> (* Magic signature *)
120 printf "ext3 superblock:\n";
121 printf " s_inodes_count = %ld\n" s_inodes_count;
122 printf " s_blocks_count = %ld\n" s_blocks_count;
123 printf " s_free_inodes_count = %ld\n" s_free_inodes_count;
124 printf " s_free_blocks_count = %ld\n" s_free_blocks_count
127 eprintf "not an ext3 superblock!\n%!";
131 Constructing packets for a simple binary message
136 +---------------+---------------+--------------------------+
137 | type | subtype | parameter |
138 +---------------+---------------+--------------------------+
139 <-- 16 bits --> <-- 16 bits --> <------- 32 bits -------->
141 All fields are in network byte order.
144 let make_message typ subtype param =
152 {2 Loading, creating bitstrings}
154 The basic data type is the {!bitstring}, a string of bits of
155 arbitrary length. Bitstrings can be any length in bits and
156 operations do not need to be byte-aligned (although they will
157 generally be more efficient if they are byte-aligned).
159 Internally a bitstring is stored as a normal OCaml [string]
160 together with an offset and length, where the offset and length are
161 measured in bits. Thus one can efficiently form substrings of
162 bitstrings, overlay a bitstring on existing data, and load and save
163 bitstrings from files or other external sources.
165 To load a bitstring from a file use {!bitstring_of_file} or
166 {!bitstring_of_chan}.
168 There are also functions to create bitstrings from arbitrary data.
169 See the {{:#reference}reference} below.
171 {2 Matching bitstrings with patterns}
173 Use the [bitmatch] operator (part of the syntax extension) to break
174 apart a bitstring into its fields. [bitmatch] works a lot like the
175 OCaml [match] operator.
177 The general form of [bitmatch] is:
179 [bitmatch] {i bitstring-expression} [with]
181 [| {] {i pattern} [} ->] {i code}
183 [| {] {i pattern} [} ->] {i code}
187 As with normal match, the statement attempts to match the
188 bitstring against each pattern in turn. If none of the patterns
189 match then the standard library [Match_failure] exception is
192 Patterns look a bit different from normal match patterns. They
193 consist of a list of bitfields separated by [;] where each bitfield
194 contains a bind variable, the width (in bits) of the field, and
195 other information. Some example patterns:
200 | { version : 8; name : 8; param : 8 } -> ...
202 (* Bitstring of at least 3 bytes. First byte is the version
203 number, second byte is a field called name, third byte is
204 a field called parameter. *)
207 printf "flag is %b\n" flag
209 (* A single flag bit (mapped into an OCaml boolean). *)
211 | { len : 4; data : 1+len } ->
212 printf "len = %d, data = 0x%Lx\n" len data
214 (* A 4-bit length, followed by 1-16 bits of data, where the
215 length of the data is computed from len. *)
217 | { ipv6_source : 128 : bitstring;
218 ipv6_dest : 128 : bitstring } -> ...
220 (* IPv6 source and destination addresses. Each is 128 bits
221 and is mapped into a bitstring type which will be a substring
222 of the main bitstring expression. *)
225 You can also add conditional when-clauses:
229 when version = 4 || version = 6 -> ...
231 (* Only match and run the code when version is 4 or 6. If
232 it isn't we will drop through to the next case. *)
235 Note that the pattern is only compared against the first part of
236 the bitstring (there may be more data in the bitstring following
237 the pattern, which is not matched). In terms of regular
238 expressions you might say that the pattern matches [^pattern], not
239 [^pattern$]. To ensure that the bitstring contains only the
240 pattern, add a length -1 bitstring to the end and test that its
241 length is zero in the when-clause:
245 rest : -1 : bitstring }
246 when Bitstring.bitstring_length rest = 0 -> ...
248 (* Only matches exactly 4 bits. *)
251 Normally the first part of each field is a binding variable,
252 but you can also match a constant, as in:
255 | { (4|6) : 4 } -> ...
257 (* Only matches if the first 4 bits contain either
258 the integer 4 or the integer 6. *)
261 One may also match on strings:
264 | { "MAGIC" : 5*8 : string } -> ...
266 (* Only matches if the string "MAGIC" appears at the start
270 {3:patternfieldreference Pattern field reference}
272 The exact format of each pattern field is:
274 [pattern : length [: qualifier [,qualifier ...]]]
276 [pattern] is the pattern, binding variable name, or constant to
277 match. [length] is the length in bits which may be either a
278 constant or an expression. The length expression is just an OCaml
279 expression and can use any values defined in the program, and refer
280 back to earlier fields (but not to later fields).
282 Integers can only have lengths in the range \[1..64\] bits. See the
283 {{:#integertypes}integer types} section below for how these are
284 mapped to the OCaml int/int32/int64 types. This is checked
285 at compile time if the length expression is constant, otherwise it is
286 checked at runtime and you will get a runtime exception eg. in
287 the case of a computed length expression.
289 A bitstring field of length -1 matches all the rest of the
290 bitstring (thus this is only useful as the last field in a
293 A bitstring field of length 0 matches an empty bitstring
294 (occasionally useful when matching optional subfields).
296 Qualifiers are a list of identifiers/expressions which control the type,
297 signedness and endianness of the field. Permissible qualifiers are:
299 - [int]: field has an integer type
300 - [string]: field is a string type
301 - [bitstring]: field is a bitstring type
302 - [signed]: field is signed
303 - [unsigned]: field is unsigned
304 - [bigendian]: field is big endian - a.k.a network byte order
305 - [littleendian]: field is little endian - a.k.a Intel byte order
306 - [nativeendian]: field is same endianness as the machine
307 - [endian (expr)]: [expr] should be an expression which evaluates to
308 a {!endian} type, ie. [LittleEndian], [BigEndian] or [NativeEndian].
309 The expression is an arbitrary OCaml expression and can use the
310 value of earlier fields in the bitmatch.
311 - [offset (expr)]: see {{:#computedoffsets}computed offsets} below.
313 The default settings are [int], [unsigned], [bigendian], no offset.
315 Note that many of these qualifiers cannot be used together,
316 eg. bitstrings do not have endianness. The syntax extension should
317 give you a compile-time error if you use incompatible qualifiers.
319 {3 Other cases in bitmatch}
321 As well as a list of fields, it is possible to name the
322 bitstring and/or have a default match case:
327 (* Default match case. *)
329 | { _ } as pkt -> ...
331 (* Default match case, with 'pkt' bound to the whole bitstring. *)
334 {2 Constructing bitstrings}
336 Bitstrings may be constructed using the [BITSTRING] operator (as an
337 expression). The [BITSTRING] operator takes a list of fields,
338 similar to the list of fields for matching:
349 (* Constructs a 16-bit bitstring with the first four bits containing
350 the integer 1, and the following 12 bits containing the integer 10,
351 arranged in network byte order. *)
353 Bitstring.hexdump_bitstring stdout bits ;;
361 The format of each field is the same as for pattern fields (see
362 {{:#patternfieldreference}Pattern field reference section}), and
363 things like computed length fields, fixed value fields, insertion
364 of bitstrings within bitstrings, etc. are all supported.
366 {3 Construction exception}
368 The [BITSTRING] operator may throw a {!Construct_failure}
369 exception at runtime.
371 Runtime errors include:
373 - int field length not in the range \[1..64\]
374 - a bitstring with a length declared which doesn't have the
375 same length at runtime
376 - trying to insert an out of range value into an int field
377 (eg. an unsigned int field which is 2 bits wide can only
378 take values in the range \[0..3\]).
380 {2:integertypes Integer types}
382 Integer types are mapped to OCaml types [bool], [int], [int32] or
383 [int64] using a system which tries to ensure that (a) the types are
384 reasonably predictable and (b) the most efficient type is
387 The rules are slightly different depending on whether the bit
388 length expression in the field is a compile-time constant or a
391 Detection of compile-time constants is quite simplistic so only
392 simple integer literals and simple expressions (eg. [5*8]) are
393 recognized as constants.
395 In any case the bit size of an integer is limited to the range
396 \[1..64\]. This is detected as a compile-time error if that is
397 possible, otherwise a runtime check is added which can throw an
398 [Invalid_argument] exception.
403 Bit size ---- OCaml type ----
404 Constant Computed expression
412 A possible future extension may allow people with 64 bit computers
413 to specify a more optimal [int] type for bit sizes in the range
414 [32..63]. If this was implemented then such code {i could not even
415 be compiled} on 32 bit platforms, so it would limit portability.
417 Another future extension may be to allow computed
418 expressions to assert min/max range for the bit size,
419 allowing a more efficient data type than int64 to be
420 used. (Of course under such circumstances there would
421 still need to be a runtime check to enforce the
424 {2 Advanced pattern-matching features}
426 {3:computedoffsets Computed offsets}
428 You can add an [offset(..)] qualifier to bitmatch patterns in order
429 to move the current offset within the bitstring forwards.
436 field2 : 8 : offset(160) } -> ...
439 matches [field1] at the start of the bitstring and [field2]
440 at 160 bits into the bitstring. The middle 152 bits go
441 unmatched (ie. can be anything).
443 The generated code is efficient. If field lengths and offsets
444 are known to be constant at compile time, then almost all
445 runtime checks are avoided. Non-constant field lengths and/or
446 non-constant offsets can result in more runtime checks being added.
448 Note that moving the offset backwards, and moving the offset in
449 [BITSTRING] constructors, are both not supported at present.
451 {3 Check expressions}
453 You can add a [check(expr)] qualifier to bitmatch patterns.
454 If the expression evaluates to false then the current match case
455 fails to match (in other words, we fall through to the next
456 match case - there is no error).
461 | { field : 16 : check (field > 100) } -> ...
464 Note the difference between a check expression and a when-clause
465 is that the when-clause is evaluated after all the fields have
466 been matched. On the other hand a check expression is evaluated
467 after the individual field has been matched, which means it is
468 potentially more efficient (if the check expression fails then
469 we don't waste any time matching later fields).
471 We wanted to use the notation [when(expr)] here, but because
472 [when] is a reserved word we could not do this.
476 A bind expression is used to change the value of a matched
480 | { len : 16 : bind (len * 8);
481 field : len : bitstring } -> ...
484 In the example, after 'len' has been matched, its value would
485 be multiplied by 8, so the width of 'field' is the matched
486 value multiplied by 8.
490 | { field : ... : bind (expr) } -> ...
492 evaluates the following after the field has been matched:
495 (* remaining fields *)
498 {3 Order of evaluation of check() and bind()}
500 The choice is arbitrary, but we have chosen that check expressions
501 are evaluated first, and bind expressions are evaluated after.
503 This means that the result of bind() is {i not} available in
504 the check expression.
506 Note that this rule applies regardless of the order of check()
507 and bind() in the source code.
511 Use [save_offset_to(variable)] to save the current bit offset
512 within the match to a variable (strictly speaking, to a pattern).
513 This variable is then made available in any [check()] and [bind()]
514 clauses in the current field, {i and} to any later fields, and
515 to the code after the [->].
522 field : 16 : save_offset_to (field_offset) } ->
523 printf "field is at bit offset %d in the match\n" field_offset
526 (In that example, [field_offset] should always have the value
529 {2 Named patterns and persistent patterns}
531 Please see {!Bitstring_persistent} for documentation on this subject.
535 Using the compiler directly you can do:
538 ocamlc -I +bitstring \
539 -pp "camlp4of bitstring.cma bitstring_persistent.cma \
540 `ocamlc -where`/bitstring/pa_bitstring.cmo" \
541 unix.cma bitstring.cma test.ml -o test
544 Simpler method using findlib:
548 -package bitstring,bitstring.syntax -syntax bitstring.syntax \
549 -linkpkg test.ml -o test
552 {2 Security and type safety}
554 {3 Security on input}
556 The main concerns for input are buffer overflows and denial
559 It is believed that this library is robust against attempted buffer
560 overflows. In addition to OCaml's normal bounds checks, we check
561 that field lengths are >= 0, and many additional checks.
563 Denial of service attacks are more problematic. We only work
564 forwards through the bitstring, thus computation will eventually
565 terminate. As for computed lengths, code such as this is thought
571 buffer : Int64.to_int len : bitstring } ->
574 The [len] field can be set arbitrarily large by an attacker, but
575 when pattern-matching against the [buffer] field this merely causes
576 a test such as [if len <= remaining_size] to fail. Even if the
577 length is chosen so that [buffer] bitstring is allocated, the
578 allocation of sub-bitstrings is efficient and doesn't involve an
579 arbitary-sized allocation or any copying.
581 However the above does not necessarily apply to strings used in
582 matching, since they may cause the library to use the
583 {!Bitstring.string_of_bitstring} function, which allocates a string.
584 So you should take care if you use the [string] type particularly
585 with a computed length that is derived from external input.
587 The main protection against attackers should be to ensure that the
588 main program will only read input bitstrings up to a certain
589 length, which is outside the scope of this library.
591 {3 Security on output}
593 As with the input side, computed lengths are believed to be
597 let len = read_untrusted_source () in
598 let buffer = allocate_bitstring () in
600 buffer : len : bitstring
604 This code merely causes a check that buffer's length is the same as
605 [len]. However the program function [allocate_bitstring] must
606 refuse to allocate an oversized buffer (but that is outside the
607 scope of this library).
609 {3 Order of evaluation}
611 In [bitmatch] statements, fields are evaluated left to right.
613 Note that the when-clause is evaluated {i last}, so if you are
614 relying on the when-clause to filter cases then your code may do a
615 lot of extra and unncessary pattern-matching work on fields which
616 may never be needed just to evaluate the when-clause. Either
617 rearrange the code to do only the first part of the match,
618 followed by the when-clause, followed by a second inner bitmatch,
619 or use a [check()] qualifier within fields.
623 The current implementation is believed to be fully type-safe,
624 and makes compile and run-time checks where appropriate. If
625 you find a case where a check is missing please submit a
626 bug report or a patch.
630 These are thought to be the current limits:
632 Integers: \[1..64\] bits.
634 Bitstrings (32 bit platforms): maximum length is limited
635 by the string size, ie. 16 MBytes.
637 Bitstrings (64 bit platforms): maximum length is thought to be
638 limited by the string size, ie. effectively unlimited.
640 Bitstrings must be loaded into memory before we can match against
641 them. Thus available memory may be considered a limit for some
644 {2:reference Reference}
648 type endian = BigEndian | LittleEndian | NativeEndian
650 val string_of_endian : endian -> string
653 type bitstring = string * int * int
654 (** [bitstring] is the basic type used to store bitstrings.
656 The type contains the underlying data (a string),
657 the current bit offset within the string and the
658 current bit length of the string (counting from the
659 bit offset). Note that the offset and length are
660 in {b bits}, not bytes.
662 Normally you don't need to use the bitstring type
663 directly, since there are functions and syntax
664 extensions which hide the details.
666 See also {!bitstring_of_string}, {!bitstring_of_file},
667 {!hexdump_bitstring}, {!bitstring_length}.
670 (** {3 Exceptions} *)
672 exception Construct_failure of string * string * int * int
673 (** [Construct_failure (message, file, line, char)] may be
674 raised by the [BITSTRING] constructor.
676 Common reasons are that values are out of range of
677 the fields that contain them, or that computed lengths
678 are impossible (eg. negative length bitfields).
680 [message] is the error message.
682 [file], [line] and [char] point to the original source
683 location of the [BITSTRING] constructor that failed.
686 (** {3 Bitstring manipulation} *)
688 val bitstring_length : bitstring -> int
689 (** [bitstring_length bitstring] returns the length of
690 the bitstring in bits.
692 Note this just returns the third field in the {!bitstring} tuple. *)
694 val subbitstring : bitstring -> int -> int -> bitstring
695 (** [subbitstring bits off len] returns a sub-bitstring
696 of the bitstring, starting at offset [off] bits and
697 with length [len] bits.
699 If the original bitstring is not long enough to do this
700 then the function raises [Invalid_argument "subbitstring"].
702 Note that this function just changes the offset and length
703 fields of the {!bitstring} tuple, so is very efficient. *)
705 val dropbits : int -> bitstring -> bitstring
706 (** Drop the first n bits of the bitstring and return a new
707 bitstring which is shorter by n bits.
709 If the length of the original bitstring is less than n bits,
710 this raises [Invalid_argument "dropbits"].
712 Note that this function just changes the offset and length
713 fields of the {!bitstring} tuple, so is very efficient. *)
715 val takebits : int -> bitstring -> bitstring
716 (** Take the first n bits of the bitstring and return a new
717 bitstring which is exactly n bits long.
719 If the length of the original bitstring is less than n bits,
720 this raises [Invalid_argument "takebits"].
722 Note that this function just changes the offset and length
723 fields of the {!bitstring} tuple, so is very efficient. *)
725 (** {3 Constructing bitstrings} *)
727 val empty_bitstring : bitstring
728 (** [empty_bitstring] is the empty, zero-length bitstring. *)
730 val create_bitstring : int -> bitstring
731 (** [create_bitstring n] creates an [n] bit bitstring
732 containing all zeroes. *)
734 val make_bitstring : int -> char -> bitstring
735 (** [make_bitstring n c] creates an [n] bit bitstring
736 containing the repeated 8 bit pattern in [c].
738 For example, [make_bitstring 16 '\x5a'] will create
739 the bitstring [0x5a5a] or in binary [0101 1010 0101 1010].
741 Note that the length is in bits, not bytes. The length does NOT
742 need to be a multiple of 8. *)
744 val zeroes_bitstring : int -> bitstring
745 (** [zeroes_bitstring] creates an [n] bit bitstring of all 0's.
747 Actually this is the same as {!create_bitstring}. *)
749 val ones_bitstring : int -> bitstring
750 (** [ones_bitstring] creates an [n] bit bitstring of all 1's. *)
752 val bitstring_of_string : string -> bitstring
753 (** [bitstring_of_string str] creates a bitstring
754 of length [String.length str * 8] (bits) containing the
757 Note that the bitstring uses [str] as the underlying
758 string (see the representation of {!bitstring}) so you
759 should not change [str] after calling this. *)
761 val bitstring_of_file : string -> bitstring
762 (** [bitstring_of_file filename] loads the named file
765 val bitstring_of_chan : in_channel -> bitstring
766 (** [bitstring_of_chan chan] loads the contents of
767 the input channel [chan] as a bitstring.
769 The length of the final bitstring is determined
770 by the remaining input in [chan], but will always
771 be a multiple of 8 bits.
773 See also {!bitstring_of_chan_max}. *)
775 val bitstring_of_chan_max : in_channel -> int -> bitstring
776 (** [bitstring_of_chan_max chan max] works like
777 {!bitstring_of_chan} but will only read up to
778 [max] bytes from the channel (or fewer if the end of input
779 occurs before that). *)
781 val bitstring_of_file_descr : Unix.file_descr -> bitstring
782 (** [bitstring_of_file_descr fd] loads the contents of
783 the file descriptor [fd] as a bitstring.
785 See also {!bitstring_of_chan}, {!bitstring_of_file_descr_max}. *)
787 val bitstring_of_file_descr_max : Unix.file_descr -> int -> bitstring
788 (** [bitstring_of_file_descr_max fd max] works like
789 {!bitstring_of_file_descr} but will only read up to
790 [max] bytes from the channel (or fewer if the end of input
791 occurs before that). *)
793 (** {3 Converting bitstrings} *)
795 val string_of_bitstring : bitstring -> string
796 (** [string_of_bitstring bitstring] converts a bitstring to a string
797 (eg. to allow comparison).
799 This function is inefficient. In the best case when the bitstring
800 is nicely byte-aligned we do a [String.sub] operation. If the
801 bitstring isn't aligned then this involves a lot of bit twiddling
802 and is particularly inefficient.
804 If the bitstring is not a multiple of 8 bits wide then the
805 final byte of the string contains the high bits set to the
806 remaining bits and the low bits set to 0. *)
808 val bitstring_to_file : bitstring -> string -> unit
809 (** [bitstring_to_file bits filename] writes the bitstring [bits]
810 to the file [filename]. It overwrites the output file.
812 Some restrictions apply, see {!bitstring_to_chan}. *)
814 val bitstring_to_chan : bitstring -> out_channel -> unit
815 (** [bitstring_to_file bits filename] writes the bitstring [bits]
816 to the channel [chan].
818 Channels are made up of bytes, bitstrings can be any bit length
819 including fractions of bytes. So this function only works
820 if the length of the bitstring is an exact multiple of 8 bits
821 (otherwise it raises [Invalid_argument "bitstring_to_chan"]).
823 Furthermore the function is efficient only in the case where
824 the bitstring is stored fully aligned, otherwise it has to
825 do inefficient bit twiddling like {!string_of_bitstring}.
827 In the common case where the bitstring was generated by the
828 [BITSTRING] operator and is an exact multiple of 8 bits wide,
829 then this function will always work efficiently.
832 (** {3 Printing bitstrings} *)
834 val hexdump_bitstring : out_channel -> bitstring -> unit
835 (** [hexdump_bitstring chan bitstring] prints the bitstring
836 to the output channel in a format similar to the
837 Unix command [hexdump -C]. *)
839 (** {3 Bitstring buffer} *)
843 val create : unit -> t
844 val contents : t -> bitstring
845 val add_bits : t -> string -> int -> unit
846 val add_bit : t -> bool -> unit
847 val add_byte : t -> int -> unit
849 (** Buffers are mainly used by the [BITSTRING] constructor, but
850 may also be useful for end users. They work much like the
851 standard library [Buffer] module. *)
853 (** {3 Miscellaneous} *)
856 (** The package name, always ["ocaml-bitstring"] *)
859 (** The package version as a string. *)
862 (** Set this variable to true to enable extended debugging.
863 This only works if debugging was also enabled in the
864 [pa_bitstring.ml] file at compile time, otherwise it
869 (* Private functions, called from generated code. Do not use
870 * these directly - they are not safe.
873 val extract_bitstring : string -> int -> int -> int -> bitstring * int * int
875 val extract_remainder : string -> int -> int -> bitstring * int * int
877 val extract_bit : string -> int -> int -> int -> bool * int * int
879 val extract_char_unsigned : string -> int -> int -> int -> int * int * int
881 val extract_int_be_unsigned : string -> int -> int -> int -> int * int * int
883 val extract_int_le_unsigned : string -> int -> int -> int -> int * int * int
885 val extract_int_ne_unsigned : string -> int -> int -> int -> int * int * int
887 val extract_int_ee_unsigned : endian -> string -> int -> int -> int -> int * int * int
889 val extract_int32_be_unsigned : string -> int -> int -> int -> int32 * int * int
891 val extract_int32_le_unsigned : string -> int -> int -> int -> int32 * int * int
893 val extract_int32_ne_unsigned : string -> int -> int -> int -> int32 * int * int
895 val extract_int32_ee_unsigned : endian -> string -> int -> int -> int -> int32 * int * int
897 val extract_int64_be_unsigned : string -> int -> int -> int -> int64 * int * int
899 val extract_int64_le_unsigned : string -> int -> int -> int -> int64 * int * int
901 val extract_int64_ne_unsigned : string -> int -> int -> int -> int64 * int * int
903 val extract_int64_ee_unsigned : endian -> string -> int -> int -> int -> int64 * int * int
905 val construct_bit : Buffer.t -> bool -> int -> exn -> unit
907 val construct_char_unsigned : Buffer.t -> int -> int -> exn -> unit
909 val construct_int_be_unsigned : Buffer.t -> int -> int -> exn -> unit
911 val construct_int_ne_unsigned : Buffer.t -> int -> int -> exn -> unit
913 val construct_int_ee_unsigned : endian -> Buffer.t -> int -> int -> exn -> unit
915 val construct_int32_be_unsigned : Buffer.t -> int32 -> int -> exn -> unit
917 val construct_int32_ne_unsigned : Buffer.t -> int32 -> int -> exn -> unit
919 val construct_int32_ee_unsigned : endian -> Buffer.t -> int32 -> int -> exn -> unit
921 val construct_int64_be_unsigned : Buffer.t -> int64 -> int -> exn -> unit
923 val construct_int64_ne_unsigned : Buffer.t -> int64 -> int -> exn -> unit
925 val construct_int64_ee_unsigned : endian -> Buffer.t -> int64 -> int -> exn -> unit
927 val construct_string : Buffer.t -> string -> unit
929 val construct_bitstring : Buffer.t -> bitstring -> unit