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[DOC] Fix platform-dependent directives and modifiers

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* 'j' and 'J' are not pointer directives.
* size of 'j' and 'J' are platform-dependent, may not be 64-bit.
* mention corresponding C types when native-size modifier is added.

Co-Authored-By: BurdetteLamar <burdettelamar@yahoo.com>
This commit is contained in:
Nobuyoshi Nakada 2023-10-06 19:03:51 +09:00
parent 7db4ce13ed
commit 7b8d472100
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1 changed files with 16 additions and 19 deletions
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doc/packed_data.rdoc
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@ -214,18 +214,16 @@ for one element in the input or output array.
s.unpack('I*')
# => [67305985, 4244504319]
==== Pointer Directives
- <tt>'j'</tt> - 64-bit pointer-width signed integer,
native-endian (like C <tt>intptr_t</tt>):
- <tt>'j'</tt> - Pointer-width signed integer, native-endian
(like C <tt>intptr_t</tt>):
s = [67305985, -50462977].pack('j*')
# => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\xFF\xFF\xFF\xFF"
s.unpack('j*')
# => [67305985, -50462977]
- <tt>'j'</tt> - 64-bit pointer-width unsigned integer,
native-endian (like C <tt>uintptr_t</tt>):
- <tt>'j'</tt> - Pointer-width unsigned integer, native-endian
(like C <tt>uintptr_t</tt>):
s = [67305985, 4244504319].pack('J*')
# => "\x01\x02\x03\x04\x00\x00\x00\x00\xFF\xFE\xFD\xFC\x00\x00\x00\x00"
@ -251,20 +249,19 @@ for one element in the input or output array.
==== Modifiers for \Integer Directives
For directives in
<tt>'i'</tt>,
<tt>'I'</tt>,
<tt>'s'</tt>,
<tt>'S'</tt>,
<tt>'l'</tt>,
<tt>'L'</tt>,
<tt>'q'</tt>,
<tt>'Q'</tt>,
<tt>'j'</tt>, and
<tt>'J'</tt>,
these modifiers may be suffixed:
For the following directives, <tt>'!'</tt> or <tt>'_'</tt> modifiers may be
suffixed as underlying platform’s native size.
- <tt>'i'</tt>, <tt>'I'</tt> - C <tt>int</tt>, always native size.
- <tt>'s'</tt>, <tt>'S'</tt> - C <tt>short</tt>.
- <tt>'l'</tt>, <tt>'L'</tt> - C <tt>long</tt>.
- <tt>'q'</tt>, <tt>'Q'</tt> - C <tt>long long</tt>, if available.
- <tt>'j'</tt>, <tt>'J'</tt> - C <tt>intptr_t</tt>, always native size.
Native size modifiers are silently ignored for always native size directives.
The endian modifiers also may be suffixed in the directives above:
- <tt>'!'</tt> or <tt>'_'</tt> - Underlying platform’s native size.
- <tt>'>'</tt> - Big-endian.
- <tt>'<'</tt> - Little-endian.