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<h4 class="subsection">9.13.10 Floating Point</h4>

<p><a name="index-i386-floating-point-954"></a><a name="index-floating-point_002c-i386-955"></a><a name="index-x86_002d64-floating-point-956"></a><a name="index-floating-point_002c-x86_002d64-957"></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-i386-958"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-i386-959"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-i386-960"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-i386-961"></a><a name="index-g_t_0040code_007bfloat_007d-directive_002c-x86_002d64-962"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-x86_002d64-963"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-x86_002d64-964"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-x86_002d64-965"></a>
     <ul>
<li>Floating point constructors are &lsquo;<samp><span class="samp">.float</span></samp>&rsquo; or &lsquo;<samp><span class="samp">.single</span></samp>&rsquo;,
&lsquo;<samp><span class="samp">.double</span></samp>&rsquo;, and &lsquo;<samp><span class="samp">.tfloat</span></samp>&rsquo; for 32-, 64-, and 80-bit formats. 
These correspond to instruction mnemonic suffixes &lsquo;<samp><span class="samp">s</span></samp>&rsquo;, &lsquo;<samp><span class="samp">l</span></samp>&rsquo;,
and &lsquo;<samp><span class="samp">t</span></samp>&rsquo;. &lsquo;<samp><span class="samp">t</span></samp>&rsquo; stands for 80-bit (ten byte) real.  The 80387
only supports this format via the &lsquo;<samp><span class="samp">fldt</span></samp>&rsquo; (load 80-bit real to stack
top) and &lsquo;<samp><span class="samp">fstpt</span></samp>&rsquo; (store 80-bit real and pop stack) instructions.

     <p><a name="index-g_t_0040code_007bword_007d-directive_002c-i386-966"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-i386-967"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-i386-968"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-i386-969"></a><a name="index-g_t_0040code_007bword_007d-directive_002c-x86_002d64-970"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-x86_002d64-971"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-x86_002d64-972"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-x86_002d64-973"></a><li>Integer constructors are &lsquo;<samp><span class="samp">.word</span></samp>&rsquo;, &lsquo;<samp><span class="samp">.long</span></samp>&rsquo; or &lsquo;<samp><span class="samp">.int</span></samp>&rsquo;, and
&lsquo;<samp><span class="samp">.quad</span></samp>&rsquo; for the 16-, 32-, and 64-bit integer formats.  The
corresponding instruction mnemonic suffixes are &lsquo;<samp><span class="samp">s</span></samp>&rsquo; (single),
&lsquo;<samp><span class="samp">l</span></samp>&rsquo; (long), and &lsquo;<samp><span class="samp">q</span></samp>&rsquo; (quad).  As with the 80-bit real format,
the 64-bit &lsquo;<samp><span class="samp">q</span></samp>&rsquo; format is only present in the &lsquo;<samp><span class="samp">fildq</span></samp>&rsquo; (load
quad integer to stack top) and &lsquo;<samp><span class="samp">fistpq</span></samp>&rsquo; (store quad integer and pop
stack) instructions. 
</ul>

   <p>Register to register operations should not use instruction mnemonic suffixes. 
&lsquo;<samp><span class="samp">fstl %st, %st(1)</span></samp>&rsquo; will give a warning, and be assembled as if you
wrote &lsquo;<samp><span class="samp">fst %st, %st(1)</span></samp>&rsquo;, since all register to register operations
use 80-bit floating point operands. (Contrast this with &lsquo;<samp><span class="samp">fstl %st, mem</span></samp>&rsquo;,
which converts &lsquo;<samp><span class="samp">%st</span></samp>&rsquo; from 80-bit to 64-bit floating point format,
then stores the result in the 4 byte location &lsquo;<samp><span class="samp">mem</span></samp>&rsquo;)

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