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160 lines
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4 years ago
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<title>Fixed-Point - Using the GNU Compiler Collection (GCC)</title>
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Permission is granted to copy, distribute and/or modify this document
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A GNU Manual
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<div class="node">
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<a name="Fixed-Point"></a>
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<a name="Fixed_002dPoint"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Named-Address-Spaces.html#Named-Address-Spaces">Named Address Spaces</a>,
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Previous: <a rel="previous" accesskey="p" href="Hex-Floats.html#Hex-Floats">Hex Floats</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.15 Fixed-Point Types</h3>
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<p><a name="index-fixed_002dpoint-types-2936"></a><a name="index-g_t_0040code_007b_005fFract_007d-data-type-2937"></a><a name="index-g_t_0040code_007b_005fAccum_007d-data-type-2938"></a><a name="index-g_t_0040code_007b_005fSat_007d-data-type-2939"></a><a name="index-g_t_0040code_007bhr_007d-fixed_002dsuffix-2940"></a><a name="index-g_t_0040code_007br_007d-fixed_002dsuffix-2941"></a><a name="index-g_t_0040code_007blr_007d-fixed_002dsuffix-2942"></a><a name="index-g_t_0040code_007bllr_007d-fixed_002dsuffix-2943"></a><a name="index-g_t_0040code_007buhr_007d-fixed_002dsuffix-2944"></a><a name="index-g_t_0040code_007bur_007d-fixed_002dsuffix-2945"></a><a name="index-g_t_0040code_007bulr_007d-fixed_002dsuffix-2946"></a><a name="index-g_t_0040code_007bullr_007d-fixed_002dsuffix-2947"></a><a name="index-g_t_0040code_007bhk_007d-fixed_002dsuffix-2948"></a><a name="index-g_t_0040code_007bk_007d-fixed_002dsuffix-2949"></a><a name="index-g_t_0040code_007blk_007d-fixed_002dsuffix-2950"></a><a name="index-g_t_0040code_007bllk_007d-fixed_002dsuffix-2951"></a><a name="index-g_t_0040code_007buhk_007d-fixed_002dsuffix-2952"></a><a name="index-g_t_0040code_007buk_007d-fixed_002dsuffix-2953"></a><a name="index-g_t_0040code_007bulk_007d-fixed_002dsuffix-2954"></a><a name="index-g_t_0040code_007bullk_007d-fixed_002dsuffix-2955"></a><a name="index-g_t_0040code_007bHR_007d-fixed_002dsuffix-2956"></a><a name="index-g_t_0040code_007bR_007d-fixed_002dsuffix-2957"></a><a name="index-g_t_0040code_007bLR_007d-fixed_002dsuffix-2958"></a><a name="index-g_t_0040code_007bLLR_007d-fixed_002dsuffix-2959"></a><a name="index-g_t_0040code_007bUHR_007d-fixed_002dsuffix-2960"></a><a name="index-g_t_0040code_007bUR_007d-fixed_002dsuffix-2961"></a><a name="index-g_t_0040code_007bULR_007d-fixed_002dsuffix-2962"></a><a name="index-g_t_0040code_007bULLR_007d-fixed_002dsuffix-2963"></a><a name="index-g_t_0040code_007bHK_007d-fixed_002dsuffix-2964"></a><a name="index-g_t_0040code_007bK_007d-fixed_002dsuffix-2965"></a><a name="index-g_t_0040code_007bLK_007d-fixed_002dsuffix-2966"></a><a name="index-g_t_0040code_007bLLK_007d-fixed_002dsuffix-2967"></a><a name="index-g_t_0040code_007bUHK_007d-fixed_002dsuffix-2968"></a><a name="index-g_t_0040code_007bUK_007d-fixed_002dsuffix-2969"></a><a name="index-g_t_0040code_007bULK_007d-fixed_002dsuffix-2970"></a><a name="index-g_t_0040code_007bULLK_007d-fixed_002dsuffix-2971"></a>
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As an extension, GNU C supports fixed-point types as
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defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point
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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 fixed-point types.
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<p>The fixed-point types are
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<code>short _Fract</code>,
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<code>_Fract</code>,
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<code>long _Fract</code>,
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<code>long long _Fract</code>,
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<code>unsigned short _Fract</code>,
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<code>unsigned _Fract</code>,
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<code>unsigned long _Fract</code>,
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<code>unsigned long long _Fract</code>,
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<code>_Sat short _Fract</code>,
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<code>_Sat _Fract</code>,
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<code>_Sat long _Fract</code>,
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<code>_Sat long long _Fract</code>,
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<code>_Sat unsigned short _Fract</code>,
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<code>_Sat unsigned _Fract</code>,
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<code>_Sat unsigned long _Fract</code>,
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<code>_Sat unsigned long long _Fract</code>,
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<code>short _Accum</code>,
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<code>_Accum</code>,
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<code>long _Accum</code>,
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<code>long long _Accum</code>,
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<code>unsigned short _Accum</code>,
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<code>unsigned _Accum</code>,
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<code>unsigned long _Accum</code>,
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<code>unsigned long long _Accum</code>,
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<code>_Sat short _Accum</code>,
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<code>_Sat _Accum</code>,
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<code>_Sat long _Accum</code>,
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<code>_Sat long long _Accum</code>,
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<code>_Sat unsigned short _Accum</code>,
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<code>_Sat unsigned _Accum</code>,
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<code>_Sat unsigned long _Accum</code>,
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<code>_Sat unsigned long long _Accum</code>.
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<p>Fixed-point data values contain fractional and optional integral parts.
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The format of fixed-point data varies and depends on the target machine.
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<p>Support for fixed-point types includes:
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<ul>
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<li>prefix and postfix increment and decrement operators (<code>++</code>, <code>--</code>)
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<li>unary arithmetic operators (<code>+</code>, <code>-</code>, <code>!</code>)
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<li>binary arithmetic operators (<code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>)
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<li>binary shift operators (<code><<</code>, <code>>></code>)
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<li>relational operators (<code><</code>, <code><=</code>, <code>>=</code>, <code>></code>)
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<li>equality operators (<code>==</code>, <code>!=</code>)
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<li>assignment operators (<code>+=</code>, <code>-=</code>, <code>*=</code>, <code>/=</code>,
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<code><<=</code>, <code>>>=</code>)
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<li>conversions to and from integer, floating-point, or fixed-point types
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</ul>
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<p>Use a suffix in a fixed-point literal constant:
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<ul>
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<li>‘<samp><span class="samp">hr</span></samp>’ or ‘<samp><span class="samp">HR</span></samp>’ for <code>short _Fract</code> and
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<code>_Sat short _Fract</code>
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<li>‘<samp><span class="samp">r</span></samp>’ or ‘<samp><span class="samp">R</span></samp>’ for <code>_Fract</code> and <code>_Sat _Fract</code>
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<li>‘<samp><span class="samp">lr</span></samp>’ or ‘<samp><span class="samp">LR</span></samp>’ for <code>long _Fract</code> and
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<code>_Sat long _Fract</code>
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<li>‘<samp><span class="samp">llr</span></samp>’ or ‘<samp><span class="samp">LLR</span></samp>’ for <code>long long _Fract</code> and
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<code>_Sat long long _Fract</code>
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<li>‘<samp><span class="samp">uhr</span></samp>’ or ‘<samp><span class="samp">UHR</span></samp>’ for <code>unsigned short _Fract</code> and
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<code>_Sat unsigned short _Fract</code>
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<li>‘<samp><span class="samp">ur</span></samp>’ or ‘<samp><span class="samp">UR</span></samp>’ for <code>unsigned _Fract</code> and
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<code>_Sat unsigned _Fract</code>
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<li>‘<samp><span class="samp">ulr</span></samp>’ or ‘<samp><span class="samp">ULR</span></samp>’ for <code>unsigned long _Fract</code> and
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<code>_Sat unsigned long _Fract</code>
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<li>‘<samp><span class="samp">ullr</span></samp>’ or ‘<samp><span class="samp">ULLR</span></samp>’ for <code>unsigned long long _Fract</code>
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and <code>_Sat unsigned long long _Fract</code>
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<li>‘<samp><span class="samp">hk</span></samp>’ or ‘<samp><span class="samp">HK</span></samp>’ for <code>short _Accum</code> and
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<code>_Sat short _Accum</code>
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<li>‘<samp><span class="samp">k</span></samp>’ or ‘<samp><span class="samp">K</span></samp>’ for <code>_Accum</code> and <code>_Sat _Accum</code>
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<li>‘<samp><span class="samp">lk</span></samp>’ or ‘<samp><span class="samp">LK</span></samp>’ for <code>long _Accum</code> and
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<code>_Sat long _Accum</code>
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<li>‘<samp><span class="samp">llk</span></samp>’ or ‘<samp><span class="samp">LLK</span></samp>’ for <code>long long _Accum</code> and
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<code>_Sat long long _Accum</code>
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<li>‘<samp><span class="samp">uhk</span></samp>’ or ‘<samp><span class="samp">UHK</span></samp>’ for <code>unsigned short _Accum</code> and
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<code>_Sat unsigned short _Accum</code>
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<li>‘<samp><span class="samp">uk</span></samp>’ or ‘<samp><span class="samp">UK</span></samp>’ for <code>unsigned _Accum</code> and
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<code>_Sat unsigned _Accum</code>
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<li>‘<samp><span class="samp">ulk</span></samp>’ or ‘<samp><span class="samp">ULK</span></samp>’ for <code>unsigned long _Accum</code> and
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<code>_Sat unsigned long _Accum</code>
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<li>‘<samp><span class="samp">ullk</span></samp>’ or ‘<samp><span class="samp">ULLK</span></samp>’ for <code>unsigned long long _Accum</code>
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and <code>_Sat unsigned long long _Accum</code>
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</ul>
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<p>GCC support of fixed-point types as specified by the draft technical report
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is incomplete:
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<ul>
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<li>Pragmas to control overflow and rounding behaviors are not implemented.
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</ul>
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<p>Fixed-point types are supported by the DWARF 2 debug information format.
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</body></html>
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