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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

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  15. A GNU Manual

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  25. <title>Decimal Float (Using the GNU Compiler Collection (GCC))</title>

  26. 

  27. <meta name="description" content="Decimal Float (Using the GNU Compiler Collection (GCC))">

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  33. <link href="Option-Index.html#Option-Index" rel="index" title="Option Index">

  34. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  35. <link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions">

  36. <link href="Hex-Floats.html#Hex-Floats" rel="next" title="Hex Floats">

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  68. 

  69. <body lang="en">

  70. <a name="Decimal-Float"></a>

  71. <div class="header">

  72. <p>

  73. 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> &nbsp; [<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>

  74. </div>

  75. <hr>

  76. <a name="Decimal-Floating-Types"></a>

  77. <h3 class="section">6.14 Decimal Floating Types</h3>

  78. <a name="index-decimal-floating-types"></a>

  79. <a name="index-_005fDecimal32-data-type"></a>

  80. <a name="index-_005fDecimal64-data-type"></a>

  81. <a name="index-_005fDecimal128-data-type"></a>

  82. <a name="index-df-integer-suffix"></a>

  83. <a name="index-dd-integer-suffix"></a>

  84. <a name="index-dl-integer-suffix"></a>

  85. <a name="index-DF-integer-suffix"></a>

  86. <a name="index-DD-integer-suffix"></a>

  87. <a name="index-DL-integer-suffix"></a>

  88. 

  89. <p>As an extension, GNU C supports decimal floating types as

  90. defined in the N1312 draft of ISO/IEC WDTR24732.  Support for decimal

  91. floating types in GCC will evolve as the draft technical report changes.

  92. Calling conventions for any target might also change.  Not all targets

  93. support decimal floating types.

  94. </p>

  95. <p>The decimal floating types are <code>_Decimal32</code>, <code>_Decimal64</code>, and

  96. <code>_Decimal128</code>.  They use a radix of ten, unlike the floating types

  97. <code>float</code>, <code>double</code>, and <code>long double</code> whose radix is not

  98. specified by the C standard but is usually two.

  99. </p>

  100. <p>Support for decimal floating types includes the arithmetic operators

  101. add, subtract, multiply, divide; unary arithmetic operators;

  102. relational operators; equality operators; and conversions to and from

  103. integer and other floating types.  Use a suffix &lsquo;<samp>df</samp>&rsquo; or

  104. &lsquo;<samp>DF</samp>&rsquo; in a literal constant of type <code>_Decimal32</code>, &lsquo;<samp>dd</samp>&rsquo;

  105. or &lsquo;<samp>DD</samp>&rsquo; for <code>_Decimal64</code>, and &lsquo;<samp>dl</samp>&rsquo; or &lsquo;<samp>DL</samp>&rsquo; for

  106. <code>_Decimal128</code>.

  107. </p>

  108. <p>GCC support of decimal float as specified by the draft technical report

  109. is incomplete:

  110. </p>

  111. <ul>

  112. <li> When the value of a decimal floating type cannot be represented in the

  113. integer type to which it is being converted, the result is undefined

  114. rather than the result value specified by the draft technical report.

  115. 

  116. </li><li> GCC does not provide the C library functionality associated with

  117. <samp>math.h</samp>, <samp>fenv.h</samp>, <samp>stdio.h</samp>, <samp>stdlib.h</samp>, and

  118. <samp>wchar.h</samp>, which must come from a separate C library implementation.

  119. Because of this the GNU C compiler does not define macro

  120. <code>__STDC_DEC_FP__</code> to indicate that the implementation conforms to

  121. the technical report.

  122. </li></ul>

  123. 

  124. <p>Types <code>_Decimal32</code>, <code>_Decimal64</code>, and <code>_Decimal128</code>

  125. are supported by the DWARF debug information format.

  126. </p>

  127. <hr>

  128. <div class="header">

  129. <p>

  130. 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> &nbsp; [<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>

  131. </div>

  132. 

  133. 

  134. 

  135. </body>

  136. </html>