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<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>’)
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