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83 lines
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<title>i386-Float - Using as</title>
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This file documents the GNU Assembler "as".
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Copyright (C) 1991, 92, 93, 94, 95, 96, 97, 98, 99, 2000, 2001, 2002,
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2006, 2007 Free Software Foundation, Inc.
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<p>
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<a name="i386_002dFloat"></a>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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<h4 class="subsection">9.13.10 Floating Point</h4>
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<p><a name="index-i386-floating-point-923"></a><a name="index-floating-point_002c-i386-924"></a><a name="index-x86_002d64-floating-point-925"></a><a name="index-floating-point_002c-x86_002d64-926"></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-_0040code_007bfloat_007d-directive_002c-i386-927"></a><a name="index-_0040code_007bsingle_007d-directive_002c-i386-928"></a><a name="index-_0040code_007bdouble_007d-directive_002c-i386-929"></a><a name="index-_0040code_007btfloat_007d-directive_002c-i386-930"></a><a name="index-_0040code_007bfloat_007d-directive_002c-x86_002d64-931"></a><a name="index-_0040code_007bsingle_007d-directive_002c-x86_002d64-932"></a><a name="index-_0040code_007bdouble_007d-directive_002c-x86_002d64-933"></a><a name="index-_0040code_007btfloat_007d-directive_002c-x86_002d64-934"></a>
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<ul>
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<li>Floating point constructors are <span class="samp">.float</span> or <span class="samp">.single</span>,
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<span class="samp">.double</span>, and <span class="samp">.tfloat</span> for 32-, 64-, and 80-bit formats.
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These correspond to instruction mnemonic suffixes <span class="samp">s</span>, <span class="samp">l</span>,
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and <span class="samp">t</span>. <span class="samp">t</span> stands for 80-bit (ten byte) real. The 80387
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only supports this format via the <span class="samp">fldt</span> (load 80-bit real to stack
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top) and <span class="samp">fstpt</span> (store 80-bit real and pop stack) instructions.
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<p><a name="index-_0040code_007bword_007d-directive_002c-i386-935"></a><a name="index-_0040code_007blong_007d-directive_002c-i386-936"></a><a name="index-_0040code_007bint_007d-directive_002c-i386-937"></a><a name="index-_0040code_007bquad_007d-directive_002c-i386-938"></a><a name="index-_0040code_007bword_007d-directive_002c-x86_002d64-939"></a><a name="index-_0040code_007blong_007d-directive_002c-x86_002d64-940"></a><a name="index-_0040code_007bint_007d-directive_002c-x86_002d64-941"></a><a name="index-_0040code_007bquad_007d-directive_002c-x86_002d64-942"></a><li>Integer constructors are <span class="samp">.word</span>, <span class="samp">.long</span> or <span class="samp">.int</span>, and
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<span class="samp">.quad</span> for the 16-, 32-, and 64-bit integer formats. The
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corresponding instruction mnemonic suffixes are <span class="samp">s</span> (single),
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<span class="samp">l</span> (long), and <span class="samp">q</span> (quad). As with the 80-bit real format,
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the 64-bit <span class="samp">q</span> format is only present in the <span class="samp">fildq</span> (load
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quad integer to stack top) and <span class="samp">fistpq</span> (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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<span class="samp">fstl %st, %st(1)</span> will give a warning, and be assembled as if you
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wrote <span class="samp">fst %st, %st(1)</span>, since all register to register operations
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use 80-bit floating point operands. (Contrast this with <span class="samp">fstl %st, mem</span>,
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which converts <span class="samp">%st</span> from 80-bit to 64-bit floating point format,
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then stores the result in the 4 byte location <span class="samp">mem</span>)
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