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180 lines
8.7 KiB
HTML
180 lines
8.7 KiB
HTML
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<title>Alignment of poly_ints (GNU Compiler Collection (GCC) Internals)</title>
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="poly_005fint.html#poly_005fint" rel="up" title="poly_int">
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<link href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" rel="next" title="Computing bounds on poly_ints">
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</head>
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<a name="Alignment-of-poly_005fints"></a>
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<div class="header">
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<p>
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Next: <a href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" accesskey="n" rel="next">Computing bounds on <code>poly_int</code>s</a>, Previous: <a href="Arithmetic-on-poly_005fints.html#Arithmetic-on-poly_005fints" accesskey="p" rel="prev">Arithmetic on <code>poly_int</code>s</a>, Up: <a href="poly_005fint.html#poly_005fint" accesskey="u" rel="up">poly_int</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Alignment-of-poly_005fints-1"></a>
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<h3 class="section">10.5 Alignment of <code>poly_int</code>s</h3>
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<p><code>poly_int</code> provides various routines for aligning values and for querying
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misalignments. In each case the alignment must be a power of 2.
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</p>
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<dl compact="compact">
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<dt>‘<samp>can_align_p (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Return true if we can align <var>value</var> up or down to the nearest multiple
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of <var>align</var> at compile time. The answer is the same for both directions.
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</p>
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</dd>
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<dt>‘<samp>can_align_down (<var>value</var>, <var>align</var>, &<var>aligned</var>)</samp>’</dt>
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<dd><p>Return true if <code>can_align_p</code>; if so, set <var>aligned</var> to the greatest
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aligned value that is less than or equal to <var>value</var>.
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</p>
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</dd>
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<dt>‘<samp>can_align_up (<var>value</var>, <var>align</var>, &<var>aligned</var>)</samp>’</dt>
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<dd><p>Return true if <code>can_align_p</code>; if so, set <var>aligned</var> to the lowest
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aligned value that is greater than or equal to <var>value</var>.
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</p>
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</dd>
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<dt>‘<samp>known_equal_after_align_down (<var>a</var>, <var>b</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Return true if we can align <var>a</var> and <var>b</var> down to the nearest
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<var>align</var> boundary at compile time and if the two results are equal.
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</p>
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</dd>
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<dt>‘<samp>known_equal_after_align_up (<var>a</var>, <var>b</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Return true if we can align <var>a</var> and <var>b</var> up to the nearest
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<var>align</var> boundary at compile time and if the two results are equal.
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</p>
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</dd>
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<dt>‘<samp>aligned_lower_bound (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Return a result that is no greater than <var>value</var> and that is aligned
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to <var>align</var>. The result will the closest aligned value for some
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indeterminate values but not necessarily for all.
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</p>
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<p>For example, suppose we are allocating an object of <var>size</var> bytes
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in a downward-growing stack whose current limit is given by <var>limit</var>.
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If the object requires <var>align</var> bytes of alignment, the new stack
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limit is given by:
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</p>
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<div class="smallexample">
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<pre class="smallexample">aligned_lower_bound (<var>limit</var> - <var>size</var>, <var>align</var>)
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</pre></div>
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</dd>
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<dt>‘<samp>aligned_upper_bound (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Likewise return a result that is no less than <var>value</var> and that is
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aligned to <var>align</var>. This is the routine that would be used for
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upward-growing stacks in the scenario just described.
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</p>
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</dd>
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<dt>‘<samp>known_misalignment (<var>value</var>, <var>align</var>, &<var>misalign</var>)</samp>’</dt>
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<dd><p>Return true if we can calculate the misalignment of <var>value</var>
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with respect to <var>align</var> at compile time, storing the result in
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<var>misalign</var> if so.
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</p>
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</dd>
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<dt>‘<samp>known_alignment (<var>value</var>)</samp>’</dt>
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<dd><p>Return the minimum alignment that <var>value</var> is known to have
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(in other words, the largest alignment that can be guaranteed
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whatever the values of the indeterminates turn out to be).
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Return 0 if <var>value</var> is known to be 0.
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</p>
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</dd>
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<dt>‘<samp>force_align_down (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Assert that <var>value</var> can be aligned down to <var>align</var> at compile
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time and return the result. When using this routine, please add a
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comment explaining why the assertion is known to hold.
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</p>
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</dd>
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<dt>‘<samp>force_align_up (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Likewise, but aligning up.
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</p>
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</dd>
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<dt>‘<samp>force_align_down_and_div (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Divide the result of <code>force_align_down</code> by <var>align</var>. Again,
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please add a comment explaining why the assertion in <code>force_align_down</code>
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is known to hold.
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</p>
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</dd>
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<dt>‘<samp>force_align_up_and_div (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Likewise for <code>force_align_up</code>.
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</p>
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</dd>
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<dt>‘<samp>force_get_misalignment (<var>value</var>, <var>align</var>)</samp>’</dt>
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<dd><p>Assert that we can calculate the misalignment of <var>value</var> with
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respect to <var>align</var> at compile time and return the misalignment.
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When using this function, please add a comment explaining why
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the assertion is known to hold.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" accesskey="n" rel="next">Computing bounds on <code>poly_int</code>s</a>, Previous: <a href="Arithmetic-on-poly_005fints.html#Arithmetic-on-poly_005fints" accesskey="p" rel="prev">Arithmetic on <code>poly_int</code>s</a>, Up: <a href="poly_005fint.html#poly_005fint" accesskey="u" rel="up">poly_int</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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