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86 lines
6.3 KiB
HTML
86 lines
6.3 KiB
HTML
4 years ago
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<title>i386-Float - Using as</title>
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<meta name="description" content="Using as">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="i386_002dDependent.html#i386_002dDependent" title="i386-Dependent">
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<link rel="prev" href="i386_002dJumps.html#i386_002dJumps" title="i386-Jumps">
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<link rel="next" href="i386_002dSIMD.html#i386_002dSIMD" title="i386-SIMD">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 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
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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</head>
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<body>
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<div class="node">
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<a name="i386-Float"></a>
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<a name="i386_002dFloat"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="i386_002dSIMD.html#i386_002dSIMD">i386-SIMD</a>,
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Previous: <a rel="previous" accesskey="p" href="i386_002dJumps.html#i386_002dJumps">i386-Jumps</a>,
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Up: <a rel="up" accesskey="u" href="i386_002dDependent.html#i386_002dDependent">i386-Dependent</a>
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<hr>
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</div>
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<h4 class="subsection">9.15.9 Floating Point</h4>
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<p><a name="index-i386-floating-point-1115"></a><a name="index-floating-point_002c-i386-1116"></a><a name="index-x86_002d64-floating-point-1117"></a><a name="index-floating-point_002c-x86_002d64-1118"></a>All 80387 floating point types except packed BCD are supported.
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(BCD support may be added without much difficulty). These data
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types are 16-, 32-, and 64- bit integers, and single (32-bit),
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double (64-bit), and extended (80-bit) precision floating point.
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Each supported type has an instruction mnemonic suffix and a constructor
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associated with it. Instruction mnemonic suffixes specify the operand's
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data type. Constructors build these data types into memory.
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<p><a name="index-g_t_0040code_007bfloat_007d-directive_002c-i386-1119"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-i386-1120"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-i386-1121"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-i386-1122"></a><a name="index-g_t_0040code_007bfloat_007d-directive_002c-x86_002d64-1123"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-x86_002d64-1124"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-x86_002d64-1125"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-x86_002d64-1126"></a>
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<ul>
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<li>Floating point constructors are ‘<samp><span class="samp">.float</span></samp>’ or ‘<samp><span class="samp">.single</span></samp>’,
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‘<samp><span class="samp">.double</span></samp>’, and ‘<samp><span class="samp">.tfloat</span></samp>’ for 32-, 64-, and 80-bit formats.
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These correspond to instruction mnemonic suffixes ‘<samp><span class="samp">s</span></samp>’, ‘<samp><span class="samp">l</span></samp>’,
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and ‘<samp><span class="samp">t</span></samp>’. ‘<samp><span class="samp">t</span></samp>’ stands for 80-bit (ten byte) real. The 80387
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only supports this format via the ‘<samp><span class="samp">fldt</span></samp>’ (load 80-bit real to stack
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top) and ‘<samp><span class="samp">fstpt</span></samp>’ (store 80-bit real and pop stack) instructions.
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<p><a name="index-g_t_0040code_007bword_007d-directive_002c-i386-1127"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-i386-1128"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-i386-1129"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-i386-1130"></a><a name="index-g_t_0040code_007bword_007d-directive_002c-x86_002d64-1131"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-x86_002d64-1132"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-x86_002d64-1133"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-x86_002d64-1134"></a><li>Integer constructors are ‘<samp><span class="samp">.word</span></samp>’, ‘<samp><span class="samp">.long</span></samp>’ or ‘<samp><span class="samp">.int</span></samp>’, and
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‘<samp><span class="samp">.quad</span></samp>’ for the 16-, 32-, and 64-bit integer formats. The
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corresponding instruction mnemonic suffixes are ‘<samp><span class="samp">s</span></samp>’ (single),
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‘<samp><span class="samp">l</span></samp>’ (long), and ‘<samp><span class="samp">q</span></samp>’ (quad). As with the 80-bit real format,
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the 64-bit ‘<samp><span class="samp">q</span></samp>’ format is only present in the ‘<samp><span class="samp">fildq</span></samp>’ (load
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quad integer to stack top) and ‘<samp><span class="samp">fistpq</span></samp>’ (store quad integer and pop
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stack) instructions.
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</ul>
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<p>Register to register operations should not use instruction mnemonic suffixes.
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‘<samp><span class="samp">fstl %st, %st(1)</span></samp>’ will give a warning, and be assembled as if you
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wrote ‘<samp><span class="samp">fst %st, %st(1)</span></samp>’, since all register to register operations
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use 80-bit floating point operands. (Contrast this with ‘<samp><span class="samp">fstl %st, mem</span></samp>’,
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which converts ‘<samp><span class="samp">%st</span></samp>’ from 80-bit to 64-bit floating point format,
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then stores the result in the 4 byte location ‘<samp><span class="samp">mem</span></samp>’)
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</body></html>
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