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| <h3 class="section">6.14 Fixed-Point Types</h3> |
| |
| <p><a name="index-fixed_002dpoint-types-2247"></a><a name="index-g_t_0040code_007b_005fFract_007d-data-type-2248"></a><a name="index-g_t_0040code_007b_005fAccum_007d-data-type-2249"></a><a name="index-g_t_0040code_007b_005fSat_007d-data-type-2250"></a><a name="index-g_t_0040code_007bhr_007d-fixed_002dsuffix-2251"></a><a name="index-g_t_0040code_007br_007d-fixed_002dsuffix-2252"></a><a name="index-g_t_0040code_007blr_007d-fixed_002dsuffix-2253"></a><a name="index-g_t_0040code_007bllr_007d-fixed_002dsuffix-2254"></a><a name="index-g_t_0040code_007buhr_007d-fixed_002dsuffix-2255"></a><a name="index-g_t_0040code_007bur_007d-fixed_002dsuffix-2256"></a><a name="index-g_t_0040code_007bulr_007d-fixed_002dsuffix-2257"></a><a name="index-g_t_0040code_007bullr_007d-fixed_002dsuffix-2258"></a><a name="index-g_t_0040code_007bhk_007d-fixed_002dsuffix-2259"></a><a name="index-g_t_0040code_007bk_007d-fixed_002dsuffix-2260"></a><a name="index-g_t_0040code_007blk_007d-fixed_002dsuffix-2261"></a><a name="index-g_t_0040code_007bllk_007d-fixed_002dsuffix-2262"></a><a name="index-g_t_0040code_007buhk_007d-fixed_002dsuffix-2263"></a><a name="index-g_t_0040code_007buk_007d-fixed_002dsuffix-2264"></a><a name="index-g_t_0040code_007bulk_007d-fixed_002dsuffix-2265"></a><a name="index-g_t_0040code_007bullk_007d-fixed_002dsuffix-2266"></a><a name="index-g_t_0040code_007bHR_007d-fixed_002dsuffix-2267"></a><a name="index-g_t_0040code_007bR_007d-fixed_002dsuffix-2268"></a><a name="index-g_t_0040code_007bLR_007d-fixed_002dsuffix-2269"></a><a name="index-g_t_0040code_007bLLR_007d-fixed_002dsuffix-2270"></a><a name="index-g_t_0040code_007bUHR_007d-fixed_002dsuffix-2271"></a><a name="index-g_t_0040code_007bUR_007d-fixed_002dsuffix-2272"></a><a name="index-g_t_0040code_007bULR_007d-fixed_002dsuffix-2273"></a><a name="index-g_t_0040code_007bULLR_007d-fixed_002dsuffix-2274"></a><a name="index-g_t_0040code_007bHK_007d-fixed_002dsuffix-2275"></a><a name="index-g_t_0040code_007bK_007d-fixed_002dsuffix-2276"></a><a name="index-g_t_0040code_007bLK_007d-fixed_002dsuffix-2277"></a><a name="index-g_t_0040code_007bLLK_007d-fixed_002dsuffix-2278"></a><a name="index-g_t_0040code_007bUHK_007d-fixed_002dsuffix-2279"></a><a name="index-g_t_0040code_007bUK_007d-fixed_002dsuffix-2280"></a><a name="index-g_t_0040code_007bULK_007d-fixed_002dsuffix-2281"></a><a name="index-g_t_0040code_007bULLK_007d-fixed_002dsuffix-2282"></a> |
| As an extension, the GNU C compiler supports fixed-point types as |
| defined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-point |
| types in GCC will evolve as the draft technical report changes. |
| Calling conventions for any target might also change. Not all targets |
| support fixed-point types. |
| |
| <p>The fixed-point types are |
| <code>short _Fract</code>, |
| <code>_Fract</code>, |
| <code>long _Fract</code>, |
| <code>long long _Fract</code>, |
| <code>unsigned short _Fract</code>, |
| <code>unsigned _Fract</code>, |
| <code>unsigned long _Fract</code>, |
| <code>unsigned long long _Fract</code>, |
| <code>_Sat short _Fract</code>, |
| <code>_Sat _Fract</code>, |
| <code>_Sat long _Fract</code>, |
| <code>_Sat long long _Fract</code>, |
| <code>_Sat unsigned short _Fract</code>, |
| <code>_Sat unsigned _Fract</code>, |
| <code>_Sat unsigned long _Fract</code>, |
| <code>_Sat unsigned long long _Fract</code>, |
| <code>short _Accum</code>, |
| <code>_Accum</code>, |
| <code>long _Accum</code>, |
| <code>long long _Accum</code>, |
| <code>unsigned short _Accum</code>, |
| <code>unsigned _Accum</code>, |
| <code>unsigned long _Accum</code>, |
| <code>unsigned long long _Accum</code>, |
| <code>_Sat short _Accum</code>, |
| <code>_Sat _Accum</code>, |
| <code>_Sat long _Accum</code>, |
| <code>_Sat long long _Accum</code>, |
| <code>_Sat unsigned short _Accum</code>, |
| <code>_Sat unsigned _Accum</code>, |
| <code>_Sat unsigned long _Accum</code>, |
| <code>_Sat unsigned long long _Accum</code>. |
| |
| <p>Fixed-point data values contain fractional and optional integral parts. |
| The format of fixed-point data varies and depends on the target machine. |
| |
| <p>Support for fixed-point types includes: |
| <ul> |
| <li>prefix and postfix increment and decrement operators (<code>++</code>, <code>--</code>) |
| <li>unary arithmetic operators (<code>+</code>, <code>-</code>, <code>!</code>) |
| <li>binary arithmetic operators (<code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>) |
| <li>binary shift operators (<code><<</code>, <code>>></code>) |
| <li>relational operators (<code><</code>, <code><=</code>, <code>>=</code>, <code>></code>) |
| <li>equality operators (<code>==</code>, <code>!=</code>) |
| <li>assignment operators (<code>+=</code>, <code>-=</code>, <code>*=</code>, <code>/=</code>, |
| <code><<=</code>, <code>>>=</code>) |
| <li>conversions to and from integer, floating-point, or fixed-point types |
| </ul> |
| |
| <p>Use a suffix in a fixed-point literal constant: |
| <ul> |
| <li>‘<samp><span class="samp">hr</span></samp>’ or ‘<samp><span class="samp">HR</span></samp>’ for <code>short _Fract</code> and |
| <code>_Sat short _Fract</code> |
| <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> |
| <li>‘<samp><span class="samp">lr</span></samp>’ or ‘<samp><span class="samp">LR</span></samp>’ for <code>long _Fract</code> and |
| <code>_Sat long _Fract</code> |
| <li>‘<samp><span class="samp">llr</span></samp>’ or ‘<samp><span class="samp">LLR</span></samp>’ for <code>long long _Fract</code> and |
| <code>_Sat long long _Fract</code> |
| <li>‘<samp><span class="samp">uhr</span></samp>’ or ‘<samp><span class="samp">UHR</span></samp>’ for <code>unsigned short _Fract</code> and |
| <code>_Sat unsigned short _Fract</code> |
| <li>‘<samp><span class="samp">ur</span></samp>’ or ‘<samp><span class="samp">UR</span></samp>’ for <code>unsigned _Fract</code> and |
| <code>_Sat unsigned _Fract</code> |
| <li>‘<samp><span class="samp">ulr</span></samp>’ or ‘<samp><span class="samp">ULR</span></samp>’ for <code>unsigned long _Fract</code> and |
| <code>_Sat unsigned long _Fract</code> |
| <li>‘<samp><span class="samp">ullr</span></samp>’ or ‘<samp><span class="samp">ULLR</span></samp>’ for <code>unsigned long long _Fract</code> |
| and <code>_Sat unsigned long long _Fract</code> |
| <li>‘<samp><span class="samp">hk</span></samp>’ or ‘<samp><span class="samp">HK</span></samp>’ for <code>short _Accum</code> and |
| <code>_Sat short _Accum</code> |
| <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> |
| <li>‘<samp><span class="samp">lk</span></samp>’ or ‘<samp><span class="samp">LK</span></samp>’ for <code>long _Accum</code> and |
| <code>_Sat long _Accum</code> |
| <li>‘<samp><span class="samp">llk</span></samp>’ or ‘<samp><span class="samp">LLK</span></samp>’ for <code>long long _Accum</code> and |
| <code>_Sat long long _Accum</code> |
| <li>‘<samp><span class="samp">uhk</span></samp>’ or ‘<samp><span class="samp">UHK</span></samp>’ for <code>unsigned short _Accum</code> and |
| <code>_Sat unsigned short _Accum</code> |
| <li>‘<samp><span class="samp">uk</span></samp>’ or ‘<samp><span class="samp">UK</span></samp>’ for <code>unsigned _Accum</code> and |
| <code>_Sat unsigned _Accum</code> |
| <li>‘<samp><span class="samp">ulk</span></samp>’ or ‘<samp><span class="samp">ULK</span></samp>’ for <code>unsigned long _Accum</code> and |
| <code>_Sat unsigned long _Accum</code> |
| <li>‘<samp><span class="samp">ullk</span></samp>’ or ‘<samp><span class="samp">ULLK</span></samp>’ for <code>unsigned long long _Accum</code> |
| and <code>_Sat unsigned long long _Accum</code> |
| </ul> |
| |
| <p>GCC support of fixed-point types as specified by the draft technical report |
| is incomplete: |
| |
| <ul> |
| <li>Pragmas to control overflow and rounding behaviors are not implemented. |
| </ul> |
| |
| <p>Fixed-point types are supported by the DWARF2 debug information format. |
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