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100 lines
4.5 KiB
HTML
100 lines
4.5 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 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 "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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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>Decimal Floating Point (Debugging with GDB)</title>
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<meta name="description" content="Decimal Floating Point (Debugging with GDB)">
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<meta name="keywords" content="Decimal Floating Point (Debugging with GDB)">
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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="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C.html#C" rel="up" title="C">
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<link href="D.html#D" rel="next" title="D">
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<link href="Debugging-C-Plus-Plus.html#Debugging-C-Plus-Plus" rel="prev" title="Debugging C Plus Plus">
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</style>
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</head>
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<body lang="en">
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<a name="Decimal-Floating-Point"></a>
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<div class="header">
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<p>
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Previous: <a href="Debugging-C-Plus-Plus.html#Debugging-C-Plus-Plus" accesskey="p" rel="prev">Debugging C Plus Plus</a>, Up: <a href="C.html#C" accesskey="u" rel="up">C</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Decimal-Floating-Point-format"></a>
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<h4 class="subsubsection">15.4.1.8 Decimal Floating Point format</h4>
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<a name="index-decimal-floating-point-format"></a>
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<p><small>GDB</small> can examine, set and perform computations with numbers in
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decimal floating point format, which in the C language correspond to the
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<code>_Decimal32</code>, <code>_Decimal64</code> and <code>_Decimal128</code> types as
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specified by the extension to support decimal floating-point arithmetic.
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</p>
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<p>There are two encodings in use, depending on the architecture: BID (Binary
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Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
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PowerPC and S/390. <small>GDB</small> will use the appropriate encoding for the
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configured target.
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</p>
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<p>Because of a limitation in <samp>libdecnumber</samp>, the library used by <small>GDB</small>
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to manipulate decimal floating point numbers, it is not possible to convert
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(using a cast, for example) integers wider than 32-bit to decimal float.
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</p>
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<p>In addition, in order to imitate <small>GDB</small>’s behaviour with binary floating
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point computations, error checking in decimal float operations ignores
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underflow, overflow and divide by zero exceptions.
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</p>
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<p>In the PowerPC architecture, <small>GDB</small> provides a set of pseudo-registers
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to inspect <code>_Decimal128</code> values stored in floating point registers.
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See <a href="PowerPC.html#PowerPC">PowerPC</a> for more details.
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</p>
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</body>
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</html>
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