README.adoc: "an current offset" -> "a current offset"

[normand.git] / README.adoc

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:py3: Python{nbsp}3

= Normand
Philippe Proulx

image::normand-logo.png[]

[.normal]
image:https://img.shields.io/pypi/v/normand.svg?label=Latest%20version[link="https://pypi.python.org/pypi/normand"]

[.lead]
_**Normand**_ is a text-to-binary processor with its own language.

This package offers both a portable {py3} module and a command-line
tool.

WARNING: This version of Normand is 0.7, meaning both the Normand
language and the module/CLI interface aren't stable.

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== Introduction

The purpose of Normand is to consume human-readable text representing
bytes and to produce the corresponding binary data.

.Simple bytes input.
====
Consider the following Normand input:

----
4f 55 32 bb $167 fe %10100111 a9 $-32
----

The generated nine bytes are:

----
4f 55 32 bb a7 fe a7 a9  e0
----
====

As you can see in the last example, the fundamental unit of the Normand
language is the _byte_. The order in which you list bytes will be the
order of the generated data.

The Normand language is more than simple lists of bytes, though. Its
main features are:

Comments, including a bunch of insignificant symbols which may improve readability::
+
Input:
+
----
ff bb %1101:0010 # This is a comment
78 29 af $192 # This too # 99 $-80
fe80::6257:18ff:fea3:4229
60:57:18:a3:42:29
10839636-5d65-4a68-8e6a-21608ddf7258
----
+
Output:
+
----
ff bb d2 78 29 af c0 99  b0 fe 80 62 57 18 ff fe
a3 42 29 60 57 18 a3 42  29 10 83 96 36 5d 65 4a
68 8e 6a 21 60 8d df 72  58
----

Hexadecimal, decimal, and binary byte constants::
+
Input:
+
----
aa bb $247 $-89 %0011_0010 %11.01= 10/10
----
+
Output:
+
----
aa bb f7 a7 32 da
----

UTF-8, UTF-16, and UTF-32 literal strings::
+
Input:
+
----
"hello world!" 00
u16le"stress\nverdict 🤣"
----
+
Output:
+
----
68 65 6c 6c 6f 20 77 6f  72 6c 64 21 00 73 00 74  ┆ hello world!•s•t
00 72 00 65 00 73 00 73  00 0a 00 76 00 65 00 72  ┆ •r•e•s•s•••v•e•r
00 64 00 69 00 63 00 74  00 20 00 3e d8 23 dd     ┆ •d•i•c•t• •>•#•
----

Labels: special variables holding the offset where they're defined::
+
----
<beg> b2 52 e3 bc 91 05
$100 $50 <chair> 33 9f fe
25 e9 89 8a <end>
----

Variables::
+
----
5e 65 {tower = 47} c6 7f f2 c4
44 {hurl = tower - 14} b5 {tower = hurl} 26 2d
----
+
The value of a variable assignment is the evaluation of a valid {py3}
expression which may include label and variable names.

Fixed-length number with a given length (8{nbsp}bits to 64{nbsp}bits) and byte order::
+
Input:
+
----
{strength = 4}
{be} 67 <lbl> 44 $178 {(end - lbl) * 8 + strength : 16} $99 <end>
{le} {-1993 : 32}
{-3.141593 : 64}
----
+
Output:
+
----
67 44 b2 00 2c 63 37 f8  ff ff 7f bd c2 82 fb 21
09 c0
----
+
The encoded number is the evaluation of a valid {py3} expression which
may include label and variable names.

https://en.wikipedia.org/wiki/LEB128[LEB128] integer::
+
Input:
+
----
aa bb cc {-1993 : sleb128} <meow> dd ee ff
{meow * 199 : uleb128}
----
+
Output:
+
----
aa bb cc b7 70 dd ee ff e3 07
----
+
The encoded integer is the evaluation of a valid {py3} expression which
may include label and variable names.

Repetition::
+
Input:
+
----
aa bb * 5 cc <zoom> "yeah\0" * {zoom * 3}
----
+
Output:
+
----
aa bb bb bb bb bb cc 79  65 61 68 00 79 65 61 68  ┆ •••••••yeah•yeah
00 79 65 61 68 00 79 65  61 68 00 79 65 61 68 00  ┆ •yeah•yeah•yeah•
79 65 61 68 00 79 65 61  68 00 79 65 61 68 00 79  ┆ yeah•yeah•yeah•y
65 61 68 00 79 65 61 68  00 79 65 61 68 00 79 65  ┆ eah•yeah•yeah•ye
61 68 00 79 65 61 68 00  79 65 61 68 00 79 65 61  ┆ ah•yeah•yeah•yea
68 00 79 65 61 68 00 79  65 61 68 00 79 65 61 68  ┆ h•yeah•yeah•yeah
00 79 65 61 68 00 79 65  61 68 00 79 65 61 68 00  ┆ •yeah•yeah•yeah•
----

Alignment::
+
Input:
+
----
{be}

        {199:32}
@64     {43:64}
@16     {-123:16}
@32~255 {5584:32}
----
+
Output:
+
----
00 00 00 c7 00 00 00 00  00 00 00 00 00 00 00 2b
ff 85 ff ff 00 00 15 d0
----

Multilevel grouping::
+
Input:
+
----
ff ((aa bb "zoom" cc) * 5) * 3 $-34 * 4
----
+
Output:
+
----
ff aa bb 7a 6f 6f 6d cc  aa bb 7a 6f 6f 6d cc aa  ┆ •••zoom•••zoom••
bb 7a 6f 6f 6d cc aa bb  7a 6f 6f 6d cc aa bb 7a  ┆ •zoom•••zoom•••z
6f 6f 6d cc aa bb 7a 6f  6f 6d cc aa bb 7a 6f 6f  ┆ oom•••zoom•••zoo
6d cc aa bb 7a 6f 6f 6d  cc aa bb 7a 6f 6f 6d cc  ┆ m•••zoom•••zoom•
aa bb 7a 6f 6f 6d cc aa  bb 7a 6f 6f 6d cc aa bb  ┆ ••zoom•••zoom•••
7a 6f 6f 6d cc aa bb 7a  6f 6f 6d cc aa bb 7a 6f  ┆ zoom•••zoom•••zo
6f 6d cc aa bb 7a 6f 6f  6d cc de de de de        ┆ om•••zoom•••••
----

Precise error reporting::
+
----
/tmp/meow.normand:10:24 - Expecting a bit (`0` or `1`).
----
+
----
/tmp/meow.normand:32:6 - Unexpected character `k`.
----
+
----
/tmp/meow.normand:24:19 - Illegal (unknown or unreachable) variable/label name `meow` in expression `(meow - 45) // 8`; the legal names are {`mix`, `zoom`}.
----
+
----
/tmp/meow.normand:18:9 - Value 315 is outside the 8-bit range when evaluating expression `end - ICITTE` at byte offset 45.
----

You can use Normand to track data source files in your favorite VCS
instead of raw binary files. The binary files that Normand generates can
be used to test file format decoding, including malformatted data, for
example, as well as for education.

See <<learn-normand>> to explore all the Normand features.

== Install Normand

Normand requires Python ≥ 3.4.

To install Normand:

----
$ python3 -m pip install --user normand
----

See
https://packaging.python.org/en/latest/tutorials/installing-packages/#installing-to-the-user-site[Installing to the User Site]
to learn more about a user site installation.

[NOTE]
====
Normand has a single module file, `normand.py`, which you can copy as is
to your project to use it (both the <<python3-api,`normand.parse()`>>
function and the <<command-line-tool,command-line tool>>).

`normand.py` has _no external dependencies_, but if you're using
Python{nbsp}3.4, you'll need a local copy of the standard `typing`
module.
====

== Learn Normand

A Normand text input is a sequence of items which represent a sequence
of raw bytes.

[[state]] During the processing of items to data, Normand relies on a
current state:

[%header%autowidth]
|===
|State variable |Description |Initial value: <<python3-api,{py3} API>> |Initial value: <<command-line-tool,CLI>>

|[[cur-offset]] Current offset
|
The current offset has an effect on the value of <<label,labels>> and of
the special `ICITTE` name in <<fixed-length-number,fixed-length
number>>, <<leb-128-integer,LEB128 integer>>, and
<<variable-assignment,variable assignment>> expression evaluation.

Each generated byte increments the current offset.

A <<current-offset-setting,current offset setting>> may change the
current offset without generating data.

An <<current-offset-alignment,current offset alignment>> generates
padding bytes to make the current offset satisfy a given alignment.
|`init_offset` parameter of the `parse()` function.
|`--offset` option.

|[[cur-bo]] Current byte order
|
The current byte order has an effect on the encoding of
<<fixed-length-number,fixed-length numbers>>.

A <<current-byte-order-setting,current byte order setting>> may change
the current byte order.
|`init_byte_order` parameter of the `parse()` function.
|`--byte-order` option.

|<<label,Labels>>
|Mapping of label names to integral values.
|`init_labels` parameter of the `parse()` function.
|One or more `--label` options.

|<<variable-assignment,Variables>>
|Mapping of variable names to integral values.
|`init_variables` parameter of the `parse()` function.
|One or more `--var` options.
|===

The available items are:

* A <<byte-constant,constant integer>> representing a single byte.

* A <<literal-string,literal string>> representing a sequence of bytes
  encoding UTF-8, UTF-16, or UTF-32 data.

* A <<current-byte-order-setting,current byte order setting>> (big or
  little endian).

* A <<fixed-length-number,fixed-length number>> (integer or
  floating point) using the <<cur-bo,current byte order>> and of which
  the value is the result of a {py3} expression.

* An <<leb128-integer,LEB128 integer>> of which the value is the result
  of a {py3} expression.

* A <<current-offset-setting,current offset setting>>.

* A <<current-offset-alignment,current offset alignment>>.

* A <<label,label>>, that is, a named constant holding the current
  offset.
+
This is similar to an assembly label.

* A <<variable-assignment,variable assignment>> associating a name to
  the integral result of an evaluated {py3} expression.

* A <<group,group>>, that is, a scoped sequence of items.

Moreover, you can <<repetition,repeat>> any item above, except an offset
or a label, a given fixed or variable number of times. This is called a
repetition.

A Normand comment may exist:

* Between items, possibly within a group.
* Between the nibbles of a constant hexadecimal byte.
* Between the bits of a constant binary byte.
* Between the last item and the ``pass:[*]`` character of a repetition,
  and between that ``pass:[*]`` character and the following number
  or expression.

A comment is anything between two ``pass:[#]`` characters on the same
line, or from ``pass:[#]`` until the end of the line. Whitespaces and
the following symbol characters are also considered comments where a
comment may exist:

----
! / \ ? & : ; . , + [ ] _ = | -
----

The latter serve to improve readability so that you may write, for
example, a MAC address or a UUID as is.

You can test the examples of this section with the `normand`
<<command-line-tool,command-line tool>> as such:

----
$ normand file | hexdump -C
----

where `file` is the name of a file containing the Normand input.

=== Byte constant

A _byte constant_ represents a single byte.

A byte constant is:

Hexadecimal form::
    Two consecutive hexits.

Decimal form::
    A decimal number after the `$` prefix.

Binary form::
    Eight bits after the `%` prefix.

====
Input:

----
ab cd [3d 8F] CC
----

Output:

----
ab cd 3d 8f cc
----
====

====
Input:

----
$192 %1100/0011 $ -77
----

Output:

----
c0 c3 b3
----
====

====
Input:

----
58f64689-6316-4d55-8a1a-04cada366172
fe80::6257:18ff:fea3:4229
----

Output:

----
58 f6 46 89 63 16 4d 55  8a 1a 04 ca da 36 61 72  ┆ X•F•c•MU•••••6ar
fe 80 62 57 18 ff fe a3  42 29                    ┆ ••bW••••B)
----
====

====
Input:

----
%01110011 %01100001 %01101100 %01110101 %01110100
----

Output:

----
73 61 6c 75 74  ┆ salut
----
====

=== Literal string

A _literal string_ represents the UTF-8-, UTF-16-, or UTF-32-encoded
bytes of a string.

The string to encode isn't implicitly null-terminated: use `\0` at the
end of the string to add a null character.

A literal string is:

. **Optional**: one of the following encodings instead of UTF-8:
+
--
[horizontal]
`u16be`:: UTF-16BE.
`u16le`:: UTF-16LE.
`u32be`:: UTF-32BE.
`u32le`:: UTF-32LE.
--

. The ``pass:["]`` prefix.

. A sequence of zero or more characters, possibly containing escape
  sequences.
+
An escape sequence is the ``\`` character followed by one of:
+
--
[horizontal]
`0`:: Null (U+0000)
`a`:: Alert (U+0007)
`b`:: Backspace (U+0008)
`e`:: Escape (U+001B)
`f`:: Form feed (U+000C)
`n`:: End of line (U+000A)
`r`:: Carriage return (U+000D)
`t`:: Character tabulation (U+0009)
`v`:: Line tabulation (U+000B)
``\``:: Reverse solidus (U+005C)
``pass:["]``:: Quotation mark (U+0022)
--

. The ``pass:["]`` suffix.

====
Input:

----
"coucou tout le monde!"
----

Output:

----
63 6f 75 63 6f 75 20 74  6f 75 74 20 6c 65 20 6d  ┆ coucou tout le m
6f 6e 64 65 21                                    ┆ onde!
----
====

====
Input:

----
u16le"I am not young enough to know everything."
----

Output:

----
49 00 20 00 61 00 6d 00  20 00 6e 00 6f 00 74 00  ┆ I• •a•m• •n•o•t•
20 00 79 00 6f 00 75 00  6e 00 67 00 20 00 65 00  ┆  •y•o•u•n•g• •e•
6e 00 6f 00 75 00 67 00  68 00 20 00 74 00 6f 00  ┆ n•o•u•g•h• •t•o•
20 00 6b 00 6e 00 6f 00  77 00 20 00 65 00 76 00  ┆  •k•n•o•w• •e•v•
65 00 72 00 79 00 74 00  68 00 69 00 6e 00 67 00  ┆ e•r•y•t•h•i•n•g•
2e 00                                             ┆ .•
----
====

====
Input:

----
u32be "\"illusion is the first\nof all pleasures\" 🦉"
----

Output:

----
00 00 00 22 00 00 00 69  00 00 00 6c 00 00 00 6c  ┆ •••"•••i•••l•••l
00 00 00 75 00 00 00 73  00 00 00 69 00 00 00 6f  ┆ •••u•••s•••i•••o
00 00 00 6e 00 00 00 20  00 00 00 69 00 00 00 73  ┆ •••n••• •••i•••s
00 00 00 20 00 00 00 74  00 00 00 68 00 00 00 65  ┆ ••• •••t•••h•••e
00 00 00 20 00 00 00 66  00 00 00 69 00 00 00 72  ┆ ••• •••f•••i•••r
00 00 00 73 00 00 00 74  00 00 00 0a 00 00 00 6f  ┆ •••s•••t•••••••o
00 00 00 66 00 00 00 20  00 00 00 61 00 00 00 6c  ┆ •••f••• •••a•••l
00 00 00 6c 00 00 00 20  00 00 00 70 00 00 00 6c  ┆ •••l••• •••p•••l
00 00 00 65 00 00 00 61  00 00 00 73 00 00 00 75  ┆ •••e•••a•••s•••u
00 00 00 72 00 00 00 65  00 00 00 73 00 00 00 22  ┆ •••r•••e•••s•••"
00 00 00 20 00 01 f9 89                           ┆ ••• ••••
----
====

=== Current byte order setting

This special item sets the <<cur-bo,_current byte order_>>.

The two accepted forms are:

[horizontal]
``pass:[{be}]``:: Set the current byte order to big endian.
``pass:[{le}]``:: Set the current byte order to little endian.

=== Fixed-length number

A _fixed-length number_ represents a fixed number of bytes encoding
either:

* An unsigned or signed integer (two's complement).
+
The available lengths are 8, 16, 24, 32, 40, 48, 56, and 64.

* A floating point number
  ([IEEE{nbsp}754-2008[https://standards.ieee.org/standard/754-2008.html]).
+
The available length are 32 (_binary32_) and 64 (_binary64_).

The value is the result of evaluating a {py3} expression using the
<<cur-bo,current byte order>>.

A fixed-length number is:

. The ``pass:[{]`` prefix.

. A valid {py3} expression.
+
For a fixed-length number at some source location{nbsp}__**L**__, this
expression may contain the name of any accessible <<label,label>> (not
within a nested group), including the name of a label defined
after{nbsp}__**L**__, as well as the name of any
<<variable-assignment,variable>> known at{nbsp}__**L**__.
+
The value of the special name `ICITTE` (`int` type) in this expression
is the <<cur-offset,current offset>> (before encoding the number).

. The `:` character.

. An encoding length in bits amongst:
+
--
The expression evaluates to an `int` value::
    `8`, `16`, `24`, `32`, `40`, `48`, `56`, and `64`.

The expression evaluates to a `float` value::
    `32` and `64`.
--

. The `}` suffix.

====
Input:

----
{le} {345:16}
{be} {-0xabcd:32}
----

Output:

----
59 01 ff ff 54 33
----
====

====
Input:

----
{be}

# String length in bits
{8 * (str_end - str_beg) : 16}

# String
<str_beg>
  "hello world!"
<str_end>
----

Output:

----
00 60 68 65 6c 6c 6f 20  77 6f 72 6c 64 21  ┆ •`hello world!
----
====

====
Input:

----
{20 - ICITTE : 8} * 10
----

Output:

----
14 13 12 11 10 0f 0e 0d  0c 0b
----
====

====
Input:

----
{le}
{2 * 0.0529 : 32}
----

Output:

----
ac ad d8 3d
----
====

=== LEB128 integer

An _LEB128 integer_ represents a variable number of bytes encoding an
unsigned or signed integer which is the result of evaluating a {py3}
expression following the https://en.wikipedia.org/wiki/LEB128[LEB128]
format.

An LEB128 integer is:

. The ``pass:[{]`` prefix.

. A valid {py3} expression.
+
For an LEB128 integer at some source location{nbsp}__**L**__, this
expression may contain:
+
--
* The name of any <<label,label>> defined before{nbsp}__**L**__.
* The name of any <<variable-assignment,variable>> known at{nbsp}__**L**__
  which doesn't, directly or indirectly, refer to a label
  defined after{nbsp}__**L**__.
--
+
The value of the special name `ICITTE` (`int` type) in this expression
is the <<cur-offset,current offset>> (before encoding the integer).

. The `:` character.

. One of:
+
--
[horizontal]
`uleb128`:: Use the unsigned LEB128 format.
`sleb128`:: Use the signed LEB128 format.
--

. The `}` suffix.

====
Input:

----
{624485 : uleb128}
----

Output:

----
e5 8e 26
----
====

====
Input:

----
aa bb cc dd
<meow>
ee ff
{-981238311 + (meow * -23) : sleb128}
"hello"
----

Output:

----
aa bb cc dd ee ff fd fa  8d ac 7c 68 65 6c 6c 6f  ┆ ••••••••••|hello
----
====

=== Current offset setting

This special item sets the <<cur-offset,_current offset_>>.

A current offset setting is:

. The `<` prefix.

. A positive integer (hexadecimal starting with `0x` or `0X` accepted)
  which is the new current offset.

. The `>` suffix.

====
Input:

----
       {ICITTE : 8} * 8
<0x61> {ICITTE : 8} * 8
----

Output:

----
00 01 02 03 04 05 06 07  61 62 63 64 65 66 67 68  ┆ ••••••••abcdefgh
----
====

====
Input:

----
aa bb cc dd <meow> ee ff
<12> 11 22 33 <mix> 44 55
{meow : 8} {mix : 8}
----

Output:

----
aa bb cc dd ee ff 11 22  33 44 55 04 0f  ┆ •••••••"3DU••
----
====

=== Current offset alignment

A _current offset alignment_ represents zero or more padding bytes to
make the <<cur-offset,current offset>> meet a given
https://en.wikipedia.org/wiki/Data_structure_alignment[alignment] value.

More specifically, for an alignment value of{nbsp}__**N**__{nbsp}bits,
a current offset alignment represents the required padding bytes until
the current offset is a multiple of __**N**__{nbsp}/{nbsp}8.

A current offset alignment is:

. The `@` prefix.

. A positive integer (hexadecimal starting with `0x` or `0X` accepted)
  which is the alignment value in _bits_.
+
This value must be greater than zero and a multiple of{nbsp}8.

. **Optional**:
+
--
. The ``pass:[~]`` prefix.
. A positive integer (hexadecimal starting with `0x` or `0X` accepted)
  which is the value of the byte to use as padding to align the
  <<cur-offset,current offset>>.
--
+
Without this section, the padding byte value is zero.

====
Input:

----
11 22 (@32 aa bb cc) * 3
----

Output:

----
11 22 00 00 aa bb cc 00  aa bb cc 00 aa bb cc
----
====

====
Input:

----
{le}
77 88
@32~0xcc {-893.5:32}
@128~0x55 "meow"
----

Output:

----
77 88 cc cc 00 60 5f c4  55 55 55 55 55 55 55 55  ┆ w••••`_•UUUUUUUU
6d 65 6f 77                                       ┆ meow
----
====

====
Input:

----
aa bb cc <29> @64~255 "zoom"
----

Output:

----
aa bb cc ff ff ff 7a 6f  6f 6d  ┆ ••••••zoom
----
====

=== Label

A _label_ associates a name to the <<cur-offset,current offset>>.

All the labels of a whole Normand input must have unique names.

A label must not share the name of a <<variable-assignment,variable>>
name.

A label is:

. The `<` prefix.

. A valid {py3} name which is not `ICITTE` (see
  <<fixed-length-number>>, <<leb128-integer>>, and
  <<variable-assignment>> to learn more).

. The `>` suffix.

=== Variable assignment

A _variable assignment_ associates a name to the integral result of an
evaluated {py3} expression.

A variable assignment is:

. The ``pass:[{]`` prefix.

. A valid {py3} name which is not `ICITTE` (see
  <<fixed-length-number>>, <<leb128-integer>>, and
  <<variable-assignment>> to learn more).

. The `=` character.

. A valid {py3} expression.
+
For a variable assignment at some source location{nbsp}__**L**__, this
expression may contain the name of any accessible <<label,label>> (not
within a nested group), including the name of a label defined
after{nbsp}__**L**__, as well as the name of any
<<variable-assignment,variable>> known at{nbsp}__**L**__.
+
The value of the special name `ICITTE` (`int` type) in this expression
is the <<cur-offset,current offset>>.

. The `}` suffix.

====
Input:

----
{mix = 101} {le}
{meow = 42} 11 22 {meow:8} 33 {meow = ICITTE + 17}
"yooo" {meow + mix : 16}
----

Output:

----
11 22 2a 33 79 6f 6f 6f  7a 00  ┆ •"*3yoooz•
----
====

=== Group

A _group_ is a scoped sequence of items.

The <<label,labels>> within a group aren't visible outside of it.

The main purpose of a group is to <<repetition,repeat>> more than a
single item.

A group is:

. The `(` prefix.

. Zero or more items.

. The `)` suffix.

====
Input:

----
((aa bb cc) dd () ee) "leclerc"
----

Output:

----
aa bb cc dd ee 6c 65 63  6c 65 72 63  ┆ •••••leclerc
----
====

====
Input:

----
((aa bb cc) * 3 dd ee) * 5
----

Output:

----
aa bb cc aa bb cc aa bb  cc dd ee aa bb cc aa bb
cc aa bb cc dd ee aa bb  cc aa bb cc aa bb cc dd
ee aa bb cc aa bb cc aa  bb cc dd ee aa bb cc aa
bb cc aa bb cc dd ee
----
====

====
Input:

----
{be}
(
  <str_beg> u16le"sébastien diaz" <str_end>
  {ICITTE - str_beg : 8}
  {(end - str_beg) * 5 : 24}
) * 3
<end>
----

Output:

----
73 00 e9 00 62 00 61 00  73 00 74 00 69 00 65 00  ┆ s•••b•a•s•t•i•e•
6e 00 20 00 64 00 69 00  61 00 7a 00 1c 00 01 e0  ┆ n• •d•i•a•z•••••
73 00 e9 00 62 00 61 00  73 00 74 00 69 00 65 00  ┆ s•••b•a•s•t•i•e•
6e 00 20 00 64 00 69 00  61 00 7a 00 1c 00 01 40  ┆ n• •d•i•a•z••••@
73 00 e9 00 62 00 61 00  73 00 74 00 69 00 65 00  ┆ s•••b•a•s•t•i•e•
6e 00 20 00 64 00 69 00  61 00 7a 00 1c 00 00 a0  ┆ n• •d•i•a•z•••••
----
====

=== Repetition

A _repetition_ represents the bytes of an item repeated a given number
of times.

A repetition is:

. Any item except:

** A <<current-byte-order-setting,current byte order setting>>.
** A <<current-offset-setting,current offset setting>>.
** A <<label,label>>.
** A <<offset-alignment,offset alignment>>.
** A <<variable-assignment,variable assignment>>.

. The ``pass:[*]`` character.

. One of:

** A positive integer (hexadecimal starting with `0x` or `0X` accepted)
   which is the number of times to repeat the previous item.

** The ``pass:[{]`` prefix, a valid {py3} expression, and the
   ``pass:[}]`` suffix.
+
For a repetition at some source location{nbsp}__**L**__, this expression
may contain:
+
--
* The name of any <<label,label>> defined before{nbsp}__**L**__ and
  which isn't part of its repeated item.
* The name of any <<variable-assignment,variable>> known
  at{nbsp}__**L**__, which isn't part of its repeated item, and which
  doesn't, directly or indirectly, refer to a label defined
  after{nbsp}__**L**__.
--
+
This expression must not contain the special name `ICITTE`.

====
Input:

----
{end - ICITTE - 1 : 8} * 0x100 <end>
----

Output:

----
ff fe fd fc fb fa f9 f8  f7 f6 f5 f4 f3 f2 f1 f0  ┆ ••••••••••••••••
ef ee ed ec eb ea e9 e8  e7 e6 e5 e4 e3 e2 e1 e0  ┆ ••••••••••••••••
df de dd dc db da d9 d8  d7 d6 d5 d4 d3 d2 d1 d0  ┆ ••••••••••••••••
cf ce cd cc cb ca c9 c8  c7 c6 c5 c4 c3 c2 c1 c0  ┆ ••••••••••••••••
bf be bd bc bb ba b9 b8  b7 b6 b5 b4 b3 b2 b1 b0  ┆ ••••••••••••••••
af ae ad ac ab aa a9 a8  a7 a6 a5 a4 a3 a2 a1 a0  ┆ ••••••••••••••••
9f 9e 9d 9c 9b 9a 99 98  97 96 95 94 93 92 91 90  ┆ ••••••••••••••••
8f 8e 8d 8c 8b 8a 89 88  87 86 85 84 83 82 81 80  ┆ ••••••••••••••••
7f 7e 7d 7c 7b 7a 79 78  77 76 75 74 73 72 71 70  ┆ •~}|{zyxwvutsrqp
6f 6e 6d 6c 6b 6a 69 68  67 66 65 64 63 62 61 60  ┆ onmlkjihgfedcba`
5f 5e 5d 5c 5b 5a 59 58  57 56 55 54 53 52 51 50  ┆ _^]\[ZYXWVUTSRQP
4f 4e 4d 4c 4b 4a 49 48  47 46 45 44 43 42 41 40  ┆ ONMLKJIHGFEDCBA@
3f 3e 3d 3c 3b 3a 39 38  37 36 35 34 33 32 31 30  ┆ ?>=<;:9876543210
2f 2e 2d 2c 2b 2a 29 28  27 26 25 24 23 22 21 20  ┆ /.-,+*)('&%$#"!
1f 1e 1d 1c 1b 1a 19 18  17 16 15 14 13 12 11 10  ┆ ••••••••••••••••
0f 0e 0d 0c 0b 0a 09 08  07 06 05 04 03 02 01 00  ┆ ••••••••••••••••
----
====

====
Input:

----
{times = 1}
aa bb cc dd
(
  <here>
  (ee ff) * {here + 1}
  11 22 33 * {times}
  {times = times + 1}
) * 3
"coucou!"
----

Output:

----
aa bb cc dd ee ff ee ff  ee ff ee ff ee ff 11 22  ┆ •••••••••••••••"
33 ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ 3•••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff 11 22 33  33 ee ff ee ff ee ff ee  ┆ ••••••"33•••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff ee ff ee  ┆ ••••••••••••••••
ff ee ff ee ff ee ff ee  ff ee ff ee ff 11 22 33  ┆ ••••••••••••••"3
33 33 63 6f 75 63 6f 75  21                       ┆ 33coucou!
----
====

====
This example shows how to use a repetition as a conditional section
depending on some predefined variable.

Input:

----
aa bb cc dd
(ee ff "meow mix" 00) * {cond}
{be} {-1993:16}
----

Output (`cond` is 0):

----
aa bb cc dd f8 37
----

Output (`cond` is 1):

----
aa bb cc dd ee ff 6d 65  6f 77 20 6d 69 78 00 f8  ┆ ••••••meow mix••
37                                                ┆ 7
----
====

== Command-line tool

If you <<install-normand,installed>> the `normand` package, then you
can use the `normand` command-line tool:

----
$ normand <<< '"ma gang de malades"' | hexdump -C
----

----
00000000  6d 61 20 67 61 6e 67 20  64 65 20 6d 61 6c 61 64  |ma gang de malad|
00000010  65 73                                             |es|
----

If you copy the `normand.py` module to your own project, then you can
run the module itself:

----
$ python3 -m normand <<< '"ma gang de malades"' | hexdump -C
----

----
00000000  6d 61 20 67 61 6e 67 20  64 65 20 6d 61 6c 61 64  |ma gang de malad|
00000010  65 73                                             |es|
----

Without a path argument, the `normand` tool reads from the standard
input.

The `normand` tool prints the generated binary data to the standard
output.

Various options control the initial <<state,state>> of the processor:
use the `--help` option to learn more.

== {py3} API

The whole `normand` package/module API is:

[source,python]
----
class ByteOrder(enum.Enum):
    # Big endian.
    BE = ...

    # Little endian.
    LE = ...


class TextLoc:
    # Line number.
    @property
    def line_no(self) -> int:
        ...

    # Column number.
    @property
    def col_no(self) -> int:
        ...


class ParseError(RuntimeError):
    # Source text location.
    @property
    def text_loc(self) -> TextLoc:
        ...


SymbolsT = typing.Dict[str, int]


class ParseResult:
    # Generated data.
    @property
    def data(self) -> bytearray:
        ...

    # Updated variable values.
    @property
    def variables(self) -> SymbolsT:
        ...

    # Updated main group label values.
    @property
    def labels(self) -> SymbolsT:
        ...

    # Final offset.
    @property
    def offset(self) -> int:
        ...

    # Final byte order.
    @property
    def byte_order(self) -> typing.Optional[ByteOrder]:
        ...


def parse(normand: str,
          init_variables: typing.Optional[SymbolsT] = None,
          init_labels: typing.Optional[SymbolsT] = None,
          init_offset: int = 0,
          init_byte_order: typing.Optional[ByteOrder] = None) -> ParseResult:
    ...
----

The `normand` parameter is the actual <<learn-normand,Normand input>>
while the other parameters control the initial <<state,state>>.

The `parse()` function raises a `ParseError` instance should it fail to
parse the `normand` string for any reason.

== Development

Normand is a https://python-poetry.org/[Poetry] project.

To develop it, install it through Poetry and enter the virtual
environment:

----
$ poetry install
$ poetry shell
$ normand <<< '"lol" * 10 0a'
----

`normand.py` is processed by:

* https://microsoft.github.io/pyright/[Pyright]
* https://github.com/psf/black[Black]
* https://pycqa.github.io/isort/[isort]

=== Testing

Use https://docs.pytest.org/[pytest] to test Normand once the package is
part of your virtual environment, for example:

----
$ poetry install
$ poetry run pip3 install pytest
$ poetry run pytest
----

The `pytest` project is currently not a development dependency in
`pyproject.toml` due to backward compatibiliy issues with
Python{nbsp}3.4.

In the `tests` directory, each `*.nt` file is a test. The file name
prefix indicates what it's meant to test:

`pass-`::
    Everything above the `---` line is the valid Normand input
    to test.
+
Everything below the `---` line is the expected data
(whitespace-separated hexadecimal bytes).

`fail-`::
    Everything above the `---` line is the invalid Normand input
    to test.
+
Everything below the `---` line is the expected error message having
this form:
+
----
LINE:COL - MESSAGE
----

=== Contributing

Normand uses https://review.lttng.org/admin/repos/normand,general[Gerrit]
for code review.

To report a bug, https://github.com/efficios/normand/issues/new[create a
GitHub issue].