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| <title>Using the GNU Compiler Collection (GCC): Decimal Float</title> |
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| Next: <a href="Hex-Floats.html#Hex-Floats" accesskey="n" rel="next">Hex Floats</a>, Previous: <a href="Half_002dPrecision.html#Half_002dPrecision" accesskey="p" rel="prev">Half-Precision</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Decimal-Floating-Types"></a> |
| <h3 class="section">6.13 Decimal Floating Types</h3> |
| <a name="index-decimal-floating-types"></a> |
| <a name="index-_005fDecimal32-data-type"></a> |
| <a name="index-_005fDecimal64-data-type"></a> |
| <a name="index-_005fDecimal128-data-type"></a> |
| <a name="index-df-integer-suffix"></a> |
| <a name="index-dd-integer-suffix"></a> |
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| |
| <p>As an extension, GNU C 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> |
| <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> |
| <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>df</samp>’ or |
| ‘<samp>DF</samp>’ in a literal constant of type <code>_Decimal32</code>, ‘<samp>dd</samp>’ |
| or ‘<samp>DD</samp>’ for <code>_Decimal64</code>, and ‘<samp>dl</samp>’ or ‘<samp>DL</samp>’ for |
| <code>_Decimal128</code>. |
| </p> |
| <p>GCC support of decimal float as specified by the draft technical report |
| is incomplete: |
| </p> |
| <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><li> GCC does not provide the C library functionality associated with |
| <samp>math.h</samp>, <samp>fenv.h</samp>, <samp>stdio.h</samp>, <samp>stdlib.h</samp>, and |
| <samp>wchar.h</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. |
| </li></ul> |
| |
| <p>Types <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code> |
| are supported by the DWARF 2 debug information format. |
| </p> |
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| Next: <a href="Hex-Floats.html#Hex-Floats" accesskey="n" rel="next">Hex Floats</a>, Previous: <a href="Half_002dPrecision.html#Half_002dPrecision" accesskey="p" rel="prev">Half-Precision</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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