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<title>Decimal Float - Using the GNU Compiler Collection (GCC)</title>
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<a name="Decimal-Float"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Hex-Floats.html#Hex-Floats">Hex Floats</a>,
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Previous: <a rel="previous" accesskey="p" href="Half_002dPrecision.html#Half_002dPrecision">Half-Precision</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<h3 class="section">6.13 Decimal Floating Types</h3>
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<p><a name="index-decimal-floating-types-2925"></a><a name="index-g_t_0040code_007b_005fDecimal32_007d-data-type-2926"></a><a name="index-g_t_0040code_007b_005fDecimal64_007d-data-type-2927"></a><a name="index-g_t_0040code_007b_005fDecimal128_007d-data-type-2928"></a><a name="index-g_t_0040code_007bdf_007d-integer-suffix-2929"></a><a name="index-g_t_0040code_007bdd_007d-integer-suffix-2930"></a><a name="index-g_t_0040code_007bdl_007d-integer-suffix-2931"></a><a name="index-g_t_0040code_007bDF_007d-integer-suffix-2932"></a><a name="index-g_t_0040code_007bDD_007d-integer-suffix-2933"></a><a name="index-g_t_0040code_007bDL_007d-integer-suffix-2934"></a>
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As an extension, GNU C supports decimal floating types as
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defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal
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floating types in GCC will evolve as the draft technical report changes.
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Calling conventions for any target might also change. Not all targets
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support decimal floating types.
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<p>The decimal floating types are <code>_Decimal32</code>, <code>_Decimal64</code>, and
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<code>_Decimal128</code>. They use a radix of ten, unlike the floating types
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<code>float</code>, <code>double</code>, and <code>long double</code> whose radix is not
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specified by the C standard but is usually two.
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<p>Support for decimal floating types includes the arithmetic operators
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add, subtract, multiply, divide; unary arithmetic operators;
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relational operators; equality operators; and conversions to and from
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integer and other floating types. Use a suffix ‘<samp><span class="samp">df</span></samp>’ or
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‘<samp><span class="samp">DF</span></samp>’ in a literal constant of type <code>_Decimal32</code>, ‘<samp><span class="samp">dd</span></samp>’
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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
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<code>_Decimal128</code>.
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<p>GCC support of decimal float as specified by the draft technical report
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is incomplete:
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<ul>
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<li>When the value of a decimal floating type cannot be represented in the
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integer type to which it is being converted, the result is undefined
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rather than the result value specified by the draft technical report.
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<li>GCC does not provide the C library functionality associated with
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<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
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<samp><span class="file">wchar.h</span></samp>, which must come from a separate C library implementation.
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Because of this the GNU C compiler does not define macro
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<code>__STDC_DEC_FP__</code> to indicate that the implementation conforms to
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the technical report.
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</ul>
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<p>Types <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code>
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are supported by the DWARF 2 debug information format.
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