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| <h4 class="subsection">9.16.9 Floating Point</h4> |
| |
| <p><a name="index-i386-floating-point-1229"></a><a name="index-floating-point_002c-i386-1230"></a><a name="index-x86_002d64-floating-point-1231"></a><a name="index-floating-point_002c-x86_002d64-1232"></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-i386-1233"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-i386-1234"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-i386-1235"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-i386-1236"></a><a name="index-g_t_0040code_007bfloat_007d-directive_002c-x86_002d64-1237"></a><a name="index-g_t_0040code_007bsingle_007d-directive_002c-x86_002d64-1238"></a><a name="index-g_t_0040code_007bdouble_007d-directive_002c-x86_002d64-1239"></a><a name="index-g_t_0040code_007btfloat_007d-directive_002c-x86_002d64-1240"></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-i386-1241"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-i386-1242"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-i386-1243"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-i386-1244"></a><a name="index-g_t_0040code_007bword_007d-directive_002c-x86_002d64-1245"></a><a name="index-g_t_0040code_007blong_007d-directive_002c-x86_002d64-1246"></a><a name="index-g_t_0040code_007bint_007d-directive_002c-x86_002d64-1247"></a><a name="index-g_t_0040code_007bquad_007d-directive_002c-x86_002d64-1248"></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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