<html lang="en"> <head> <title>i386-Float - Using as</title> <meta http-equiv="Content-Type" content="text/html"> <meta name="description" content="Using as"> <meta name="generator" content="makeinfo 4.13"> <link title="Top" rel="start" href="index.html#Top"> <link rel="up" href="i386_002dDependent.html#i386_002dDependent" title="i386-Dependent"> <link rel="prev" href="i386_002dJumps.html#i386_002dJumps" title="i386-Jumps"> <link rel="next" href="i386_002dSIMD.html#i386_002dSIMD" title="i386-SIMD"> <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> <!-- This file documents the GNU Assembler "as". Copyright (C) 1991-2015 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. --> <meta http-equiv="Content-Style-Type" content="text/css"> <style type="text/css"><!-- pre.display { font-family:inherit } pre.format { font-family:inherit } pre.smalldisplay { font-family:inherit; font-size:smaller } pre.smallformat { font-family:inherit; font-size:smaller } pre.smallexample { font-size:smaller } pre.smalllisp { font-size:smaller } span.sc { font-variant:small-caps } span.roman { font-family:serif; font-weight:normal; } span.sansserif { font-family:sans-serif; font-weight:normal; } --></style> </head> <body> <div class="node"> <a name="i386-Float"></a> <a name="i386_002dFloat"></a> <p> Next: <a rel="next" accesskey="n" href="i386_002dSIMD.html#i386_002dSIMD">i386-SIMD</a>, Previous: <a rel="previous" accesskey="p" href="i386_002dJumps.html#i386_002dJumps">i386-Jumps</a>, Up: <a rel="up" accesskey="u" href="i386_002dDependent.html#i386_002dDependent">i386-Dependent</a> <hr> </div> <h4 class="subsection">9.15.9 Floating Point</h4> <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. (BCD support may be added without much difficulty). These data types are 16-, 32-, and 64- bit integers, and single (32-bit), double (64-bit), and extended (80-bit) precision floating point. Each supported type has an instruction mnemonic suffix and a constructor associated with it. Instruction mnemonic suffixes specify the operand's data type. Constructors build these data types into memory. <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> <ul> <li>Floating point constructors are ‘<samp><span class="samp">.float</span></samp>’ or ‘<samp><span class="samp">.single</span></samp>’, ‘<samp><span class="samp">.double</span></samp>’, and ‘<samp><span class="samp">.tfloat</span></samp>’ for 32-, 64-, and 80-bit formats. These correspond to instruction mnemonic suffixes ‘<samp><span class="samp">s</span></samp>’, ‘<samp><span class="samp">l</span></samp>’, and ‘<samp><span class="samp">t</span></samp>’. ‘<samp><span class="samp">t</span></samp>’ stands for 80-bit (ten byte) real. The 80387 only supports this format via the ‘<samp><span class="samp">fldt</span></samp>’ (load 80-bit real to stack top) and ‘<samp><span class="samp">fstpt</span></samp>’ (store 80-bit real and pop stack) instructions. <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 ‘<samp><span class="samp">.quad</span></samp>’ for the 16-, 32-, and 64-bit integer formats. The corresponding instruction mnemonic suffixes are ‘<samp><span class="samp">s</span></samp>’ (single), ‘<samp><span class="samp">l</span></samp>’ (long), and ‘<samp><span class="samp">q</span></samp>’ (quad). As with the 80-bit real format, the 64-bit ‘<samp><span class="samp">q</span></samp>’ format is only present in the ‘<samp><span class="samp">fildq</span></samp>’ (load quad integer to stack top) and ‘<samp><span class="samp">fistpq</span></samp>’ (store quad integer and pop stack) instructions. </ul> <p>Register to register operations should not use instruction mnemonic suffixes. ‘<samp><span class="samp">fstl %st, %st(1)</span></samp>’ will give a warning, and be assembled as if you wrote ‘<samp><span class="samp">fst %st, %st(1)</span></samp>’, since all register to register operations use 80-bit floating point operands. (Contrast this with ‘<samp><span class="samp">fstl %st, mem</span></samp>’, which converts ‘<samp><span class="samp">%st</span></samp>’ from 80-bit to 64-bit floating point format, then stores the result in the 4 byte location ‘<samp><span class="samp">mem</span></samp>’) </body></html>