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ICU-225 doc data align==sizeof(double)

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Markus Scherer 2000-01-13 15:31:29 +00:00
parent 248c17858b
commit 440109c8e7
1 changed files with 13 additions and 6 deletions
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icu4c/docs/udata.html
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@ -8,8 +8,6 @@
<h1>ICU - Formats and API for Binary Data Files</h1>
<p>This is a raw draft.</p>
<h2>Finding ICU data</h2>
<p>ICU data, when stored in files, is loaded from the file system
@ -52,8 +50,15 @@ Here are some points to consider:</p>
<ul>
<li>The data memory starts at an offset within the data file
that is divisible by 16 if you use <code>unewdata.h/.c</code>
to write the data.</li>
that is divisible by (at least) <code>sizeof(double)</code>
(the largest scalar data type)
if you use <code>unewdata.h/.c</code>
to write the data.
To be exact, <code>unewdata</code> writes the data 16-aligned,
and it is 16-aligned in memory-mapped files. However, the build
process forced us to insert a <code>double</code> before the
binary data to get any alignment, thus only 8-aligning
(<code>sizeof(double)==8</code> on most machines) the data.</li>
<li>Write explicitly sized values: explicitly 32 bits with an
<code>int32_t</code>, not using an ambiguous <code>int</code>.</li>
<li>Align all values according to their data type size:
@ -130,7 +135,7 @@ If the file also contains <code>char[]</code> strings,
then it can be easily shared among all big-endian <em>and</em>
ASCII-based machines, but not with (e.g.) an OS/390.<br>
OS/390 and OS/400 systems, however, could easily share such
a data file.</p>
a data file <em>created</em> on either of <em>these</em> systems.</p>
<p>To make sure that the relevant platform properties of
the data file and the loading machine match, the
@ -145,8 +150,10 @@ a different platform to begin with, especially data files packaged as DLLs
<h2>Writing a binary data file</h2>
<p>This is a raw draft.</p>
<p>... Use <code>icu/source/tools/toolutil/unewdata.h|.c</code> to write data files,
can include a copyright statement or other comment...</p>
can include a copyright statement or other comment...See <code>icu/source/tools/gennames</code>...</p>
</body>