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189 lines
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189 lines
9.6 KiB
HTML
4 years ago
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Converting poly_ints (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Converting poly_ints (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Converting poly_ints (GNU Compiler Collection (GCC) Internals)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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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="Miscellaneous-poly_005fint-routines.html#Miscellaneous-poly_005fint-routines" rel="next" title="Miscellaneous poly_int routines">
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<link href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" rel="prev" title="Computing bounds on poly_ints">
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</head>
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<body lang="en">
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<a name="Converting-poly_005fints"></a>
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<div class="header">
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<p>
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Next: <a href="Miscellaneous-poly_005fint-routines.html#Miscellaneous-poly_005fint-routines" accesskey="n" rel="next">Miscellaneous <code>poly_int</code> routines</a>, Previous: <a href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" accesskey="p" rel="prev">Computing bounds 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="Converting-poly_005fints-1"></a>
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<h3 class="section">10.7 Converting <code>poly_int</code>s</h3>
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<p>A <code>poly_int<<var>n</var>, <var>T</var>></code> can be constructed from up to
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<var>n</var> individual <var>T</var> coefficients, with the remaining coefficients
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being implicitly zero. In particular, this means that every
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<code>poly_int<<var>n</var>, <var>T</var>></code> can be constructed from a single
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scalar <var>T</var>, or something compatible with <var>T</var>.
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</p>
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<p>Also, a <code>poly_int<<var>n</var>, <var>T</var>></code> can be constructed from
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a <code>poly_int<<var>n</var>, <var>U</var>></code> if <var>T</var> can be constructed
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from <var>U</var>.
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</p>
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<p>The following functions provide other forms of conversion,
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or test whether such a conversion would succeed.
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</p>
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<dl compact="compact">
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<dt>‘<samp><var>value</var>.is_constant ()</samp>’</dt>
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<dd><p>Return true if <code>poly_int</code> <var>value</var> is a compile-time constant.
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.is_constant (&<var>c1</var>)</samp>’</dt>
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<dd><p>Return true if <code>poly_int</code> <var>value</var> is a compile-time constant,
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storing it in <var>c1</var> if so. <var>c1</var> must be able to hold all
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constant values of <var>value</var> without loss of precision.
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.to_constant ()</samp>’</dt>
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<dd><p>Assert that <var>value</var> is a compile-time constant and return its value.
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When using this function, please add a comment explaining why the
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condition is known to hold (for example, because an earlier phase
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of analysis rejected non-constants).
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.to_shwi (&<var>p2</var>)</samp>’</dt>
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<dd><p>Return true if ‘<samp>poly_int<<var>N</var>, <var>T</var>></samp>’ <var>value</var> can be
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represented without loss of precision as a
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‘<samp>poly_int<<var>N</var>, <code>HOST_WIDE_INT</code>></samp>’, storing it in that
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form in <var>p2</var> if so.
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.to_uhwi (&<var>p2</var>)</samp>’</dt>
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<dd><p>Return true if ‘<samp>poly_int<<var>N</var>, <var>T</var>></samp>’ <var>value</var> can be
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represented without loss of precision as a
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‘<samp>poly_int<<var>N</var>, <code>unsigned HOST_WIDE_INT</code>></samp>’, storing it in that
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form in <var>p2</var> if so.
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.force_shwi ()</samp>’</dt>
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<dd><p>Forcibly convert each coefficient of ‘<samp>poly_int<<var>N</var>, <var>T</var>></samp>’
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<var>value</var> to <code>HOST_WIDE_INT</code>, truncating any that are out of range.
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Return the result as a ‘<samp>poly_int<<var>N</var>, <code>HOST_WIDE_INT</code>></samp>’.
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</p>
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</dd>
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<dt>‘<samp><var>value</var>.force_uhwi ()</samp>’</dt>
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<dd><p>Forcibly convert each coefficient of ‘<samp>poly_int<<var>N</var>, <var>T</var>></samp>’
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<var>value</var> to <code>unsigned HOST_WIDE_INT</code>, truncating any that are
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out of range. Return the result as a
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‘<samp>poly_int<<var>N</var>, <code>unsigned HOST_WIDE_INT</code>></samp>’.
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</p>
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</dd>
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<dt>‘<samp>wi::shwi (<var>value</var>, <var>precision</var>)</samp>’</dt>
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<dd><p>Return a <code>poly_int</code> with the same value as <var>value</var>, but with
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the coefficients converted from <code>HOST_WIDE_INT</code> to <code>wide_int</code>.
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<var>precision</var> specifies the precision of the <code>wide_int</code> cofficients;
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if this is wider than a <code>HOST_WIDE_INT</code>, the coefficients of
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<var>value</var> will be sign-extended to fit.
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</p>
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</dd>
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<dt>‘<samp>wi::uhwi (<var>value</var>, <var>precision</var>)</samp>’</dt>
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<dd><p>Like <code>wi::shwi</code>, except that <var>value</var> has coefficients of
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type <code>unsigned HOST_WIDE_INT</code>. If <var>precision</var> is wider than
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a <code>HOST_WIDE_INT</code>, the coefficients of <var>value</var> will be
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zero-extended to fit.
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</p>
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</dd>
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<dt>‘<samp>wi::sext (<var>value</var>, <var>precision</var>)</samp>’</dt>
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<dd><p>Return a <code>poly_int</code> of the same type as <var>value</var>, sign-extending
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every coefficient from the low <var>precision</var> bits. This in effect
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applies <code>wi::sext</code> to each coefficient individually.
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</p>
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</dd>
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<dt>‘<samp>wi::zext (<var>value</var>, <var>precision</var>)</samp>’</dt>
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<dd><p>Like <code>wi::sext</code>, but for zero extension.
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</p>
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</dd>
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<dt>‘<samp>poly_wide_int::from (<var>value</var>, <var>precision</var>, <var>sign</var>)</samp>’</dt>
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<dd><p>Convert <var>value</var> to a <code>poly_wide_int</code> in which each coefficient
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has <var>precision</var> bits. Extend the coefficients according to
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<var>sign</var> if the coefficients have fewer bits.
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</p>
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</dd>
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<dt>‘<samp>poly_offset_int::from (<var>value</var>, <var>sign</var>)</samp>’</dt>
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<dd><p>Convert <var>value</var> to a <code>poly_offset_int</code>, extending its coefficients
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according to <var>sign</var> if they have fewer bits than <code>offset_int</code>.
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</p>
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</dd>
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<dt>‘<samp>poly_widest_int::from (<var>value</var>, <var>sign</var>)</samp>’</dt>
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<dd><p>Convert <var>value</var> to a <code>poly_widest_int</code>, extending its coefficients
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according to <var>sign</var> if they have fewer bits than <code>widest_int</code>.
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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="Miscellaneous-poly_005fint-routines.html#Miscellaneous-poly_005fint-routines" accesskey="n" rel="next">Miscellaneous <code>poly_int</code> routines</a>, Previous: <a href="Computing-bounds-on-poly_005fints.html#Computing-bounds-on-poly_005fints" accesskey="p" rel="prev">Computing bounds 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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