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Add back summary table for pack/unpack directives (#12349)

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* Add back summary table for pack/unpack directives
* This concise summary is very helpful e.g. to find the right Integer
  directive, and is much better at getting an overview than very long text.
* From https://github.com/ruby/ruby/pull/6567
* I merged the tables for Array#pack and String#unpack,
  there were almost the same except for String and Misc. directives.
* Tune up the tabular data and moves it to the top.

Co-authored-by: Burdette Lamar <BurdetteLamar@Yahoo.com>
Co-authored-by: Stan Lo <stan001212@gmail.com>
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Benoit Daloze 2024-12-16 22:44:34 +01:00 committed by GitHub
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commit b72e8ab816
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Notes: git 2024-12-16 21:44:53 +00:00 
Merged-By: eregon <eregontp@gmail.com>
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doc/packed_data.rdoc
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@ -1,5 +1,106 @@
= Packed \Data
== Quick Reference
These tables summarize the directives for packing and unpacking.
=== For Integers
Directive | Meaning
--------------|---------------------------------------------------------------
C | 8-bit unsigned (unsigned char)
S | 16-bit unsigned, native endian (uint16_t)
L | 32-bit unsigned, native endian (uint32_t)
Q | 64-bit unsigned, native endian (uint64_t)
J | pointer width unsigned, native endian (uintptr_t)
c | 8-bit signed (signed char)
s | 16-bit signed, native endian (int16_t)
l | 32-bit signed, native endian (int32_t)
q | 64-bit signed, native endian (int64_t)
j | pointer width signed, native endian (intptr_t)
S_ S! | unsigned short, native endian
I I_ I! | unsigned int, native endian
L_ L! | unsigned long, native endian
Q_ Q! | unsigned long long, native endian
| (raises ArgumentError if the platform has no long long type)
J! | uintptr_t, native endian (same with J)
s_ s! | signed short, native endian
i i_ i! | signed int, native endian
l_ l! | signed long, native endian
q_ q! | signed long long, native endian
| (raises ArgumentError if the platform has no long long type)
j! | intptr_t, native endian (same with j)
S> s> S!> s!> | each the same as the directive without >, but big endian
L> l> L!> l!> | S> is the same as n
I!> i!> | L> is the same as N
Q> q> Q!> q!> |
J> j> J!> j!> |
S< s< S!< s!< | each the same as the directive without <, but little endian
L< l< L!< l!< | S< is the same as v
I!< i!< | L< is the same as V
Q< q< Q!< q!< |
J< j< J!< j!< |
n | 16-bit unsigned, network (big-endian) byte order
N | 32-bit unsigned, network (big-endian) byte order
v | 16-bit unsigned, VAX (little-endian) byte order
V | 32-bit unsigned, VAX (little-endian) byte order
U | UTF-8 character
w | BER-compressed integer
=== For Floats
Directive | Meaning
----------|--------------------------------------------------
D d | double-precision, native format
F f | single-precision, native format
E | double-precision, little-endian byte order
e | single-precision, little-endian byte order
G | double-precision, network (big-endian) byte order
g | single-precision, network (big-endian) byte order
=== For Strings
Directive | Meaning
----------|-----------------------------------------------------------------
A | arbitrary binary string (remove trailing nulls and ASCII spaces)
a | arbitrary binary string
Z | null-terminated string
B | bit string (MSB first)
b | bit string (LSB first)
H | hex string (high nibble first)
h | hex string (low nibble first)
u | UU-encoded string
M | quoted-printable, MIME encoding (see RFC2045)
m | base64 encoded string (RFC 2045) (default)
| (base64 encoded string (RFC 4648) if followed by 0)
P | pointer to a structure (fixed-length string)
p | pointer to a null-terminated string
=== Additional Directives for Packing
Directive | Meaning
----------|----------------------------------------------------------------
@ | moves to absolute position
X | back up a byte
x | null byte
=== Additional Directives for Unpacking
Directive | Meaning
----------|----------------------------------------------------------------
@ | skip to the offset given by the length argument
X | skip backward one byte
x | skip forward one byte
== Packing and Unpacking
Certain Ruby core methods deal with packing and unpacking data:
- \Method Array#pack: