jeanlemotan
111 lines
4.2 KiB
HTML
111 lines
4.2 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head>
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<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
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<Title>EAAlignment</title>
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<link type="text/css" rel="stylesheet" href="UTFDoc.css">
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<meta name="author" content="Paul Pedriana">
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</head>
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<body bgcolor="#FFFFFF">
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<h1>EAAlignment</h1>
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<h2>Introduction</h2>
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<p>EAAlignment provides a number of utilities for working with variable alignment. These include:</p>
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<blockquote>
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<table border="1">
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<tr>
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<td><strong>Entity</strong></td>
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<td><strong>Description</strong></td>
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</tr>
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<tr>
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<td>EAAlignOf(type)</td>
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<td valign="top">Macro which returns the alignment of the given type as a constant expression. </td>
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</tr>
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<tr>
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<td>AlignOf<T></td>
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<td valign="top">Template which returns the alignment of the given type. </td>
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</tr>
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<tr>
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<td>AlignAddressUp<br>
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AlignAddressDown</td>
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<td valign="top">Function which aligns an arbitrary address up or down to the next user-supplied power of two. </td>
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</tr>
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<tr>
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<td>AlignObjectUp<br>
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AlignObjectDown</td>
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<td valign="top">Function which aligns an arbitrary object up or down to the next user-supplied power of two. </td>
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</tr>
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<tr>
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<td>GetAlignment<br>
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IsAddressAligned<br>
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IsObjectAligned<T><br>
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IsAligned<T><br></td>
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<td valign="top">Gets information about alignment. </td>
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</tr>
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<tr>
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<td>AlignedType</td>
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<td valign="top">Template which portably allows the re-typing of a class to have a specific alignment. </td>
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</tr>
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<tr>
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<td>AlignedArray</td>
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<td valign="top">Template which implements an array of an arbitrary class with a given alignment.</td>
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</tr>
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<tr>
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<td>AlignedObject</td>
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<td valign="top">Template which implements an instance of an arbitrary class with a given alignment.</td>
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</tr>
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<tr>
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<td>ReadMisalignedUint16<br>
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ReadMisalignedUint32<br>
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ReadMisalignedUint64</td>
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<td valign="top">Function which safely and portably reads potentially misaligned memory. </td>
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</tr>
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<tr>
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<td>WriteMisalignedUint16<br>
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WriteMisalignedUint32<br>
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WriteMisalignedUint64</td>
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<td valign="top">Function which safely and portably writes potentially misaligned memory. </td>
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</tr>
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</table>
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</blockquote>
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<p>We'll discuss some of these briefly.</p>
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<h2>EAAlignOf</h2>
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<p>EAAlignOf is your basic macro for retrieving the alignment of an object by its type. Recent versions of EABase define EA_ALIGN_OF, so EAAlignOf is currently a duplication of the EABase functionality. </p>
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<p>Example usage: </p>
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<pre class="code-example">printf("Alignment of type 'int' is %u.\n", (unsigned)EAAlignOf(int)); </pre>
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<h2>AlignedType</h2>
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<p> This class makes an aligned typedef for a given class based on a user-supplied class and alignment. This class exists because of a weakness in VC++ whereby it can only accept __declspec(align) and thus EA_PREFIX_ALIGN usage via an integer literal (e.g. "16") and not an otherwise equivalent constant integral expression (e.g. sizeof Foo).</p>
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<p>Example usage: </p>
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<pre class="code-example">const size_t kAlignment = 32; <span class="code-example-comment">// Note that in this case the alignment is defined elsewhere as a non-literal.</span><br>
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AlignedType<Widget, kAlignment>::Type widgetAlign128;<br>
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widgetAlign128.DoSomething();</pre>
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<h2>ReadMisaligned16/32/64</h2>
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<p>ReadMisaligned reads an unsigned integer from a possibly non-aligned address. The MIPS processor on the PS2, for example, cannot read a 32-bit value from an unaligned address. This function can be used to make reading such misaligned data portable.. </p>
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<p>Example usage: </p>
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<pre class="code-example">void DoSomeReading(const char* pData)
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{
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uint16_t x = ReadMisalignedUint16(pData);
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pData += sizeof(uint16_t);
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uint32_t y = ReadMisalignedUint32(pData);
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pData += sizeof(uint32_t);
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uint64_t z = ReadMisalignedUint64(pData);
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pData += sizeof(uint64_t);
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...
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}</pre>
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<hr>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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<p> </p>
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</body></html>
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