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| <h3 class="section">6.12 Decimal Floating Types</h3> |
| |
| <p><a name="index-decimal-floating-types-2236"></a><a name="index-g_t_0040code_007b_005fDecimal32_007d-data-type-2237"></a><a name="index-g_t_0040code_007b_005fDecimal64_007d-data-type-2238"></a><a name="index-g_t_0040code_007b_005fDecimal128_007d-data-type-2239"></a><a name="index-g_t_0040code_007bdf_007d-integer-suffix-2240"></a><a name="index-g_t_0040code_007bdd_007d-integer-suffix-2241"></a><a name="index-g_t_0040code_007bdl_007d-integer-suffix-2242"></a><a name="index-g_t_0040code_007bDF_007d-integer-suffix-2243"></a><a name="index-g_t_0040code_007bDD_007d-integer-suffix-2244"></a><a name="index-g_t_0040code_007bDL_007d-integer-suffix-2245"></a> |
| As an extension, the GNU C compiler supports decimal floating types as |
| defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal |
| floating types in GCC will evolve as the draft technical report changes. |
| Calling conventions for any target might also change. Not all targets |
| support decimal floating types. |
| |
| <p>The decimal floating types are <code>_Decimal32</code>, <code>_Decimal64</code>, and |
| <code>_Decimal128</code>. They use a radix of ten, unlike the floating types |
| <code>float</code>, <code>double</code>, and <code>long double</code> whose radix is not |
| specified by the C standard but is usually two. |
| |
| <p>Support for decimal floating types includes the arithmetic operators |
| add, subtract, multiply, divide; unary arithmetic operators; |
| relational operators; equality operators; and conversions to and from |
| integer and other floating types. Use a suffix ‘<samp><span class="samp">df</span></samp>’ or |
| ‘<samp><span class="samp">DF</span></samp>’ in a literal constant of type <code>_Decimal32</code>, ‘<samp><span class="samp">dd</span></samp>’ |
| or ‘<samp><span class="samp">DD</span></samp>’ for <code>_Decimal64</code>, and ‘<samp><span class="samp">dl</span></samp>’ or ‘<samp><span class="samp">DL</span></samp>’ for |
| <code>_Decimal128</code>. |
| |
| <p>GCC support of decimal float as specified by the draft technical report |
| is incomplete: |
| |
| <ul> |
| <li>When the value of a decimal floating type cannot be represented in the |
| integer type to which it is being converted, the result is undefined |
| rather than the result value specified by the draft technical report. |
| |
| <li>GCC does not provide the C library functionality associated with |
| <samp><span class="file">math.h</span></samp>, <samp><span class="file">fenv.h</span></samp>, <samp><span class="file">stdio.h</span></samp>, <samp><span class="file">stdlib.h</span></samp>, and |
| <samp><span class="file">wchar.h</span></samp>, which must come from a separate C library implementation. |
| Because of this the GNU C compiler does not define macro |
| <code>__STDC_DEC_FP__</code> to indicate that the implementation conforms to |
| the technical report. |
| </ul> |
| |
| <p>Types <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code> |
| are supported by the DWARF2 debug information format. |
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