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6.1.7 Fixed-Point Types ¶

As an extension, GNU C supports fixed-point types asdefined in the N1169 draft of ISO/IEC DTR 18037. Support for fixed-pointtypes in GCC will evolve as the draft technical report changes.Calling conventions for any target might also change. Not all targetssupport fixed-point types.

The fixed-point types areshort _Fract,_Fract,long _Fract,long long _Fract,unsigned short _Fract,unsigned _Fract,unsigned long _Fract,unsigned long long _Fract,_Sat short _Fract,_Sat _Fract,_Sat long _Fract,_Sat long long _Fract,_Sat unsigned short _Fract,_Sat unsigned _Fract,_Sat unsigned long _Fract,_Sat unsigned long long _Fract,short _Accum,_Accum,long _Accum,long long _Accum,unsigned short _Accum,unsigned _Accum,unsigned long _Accum,unsigned long long _Accum,_Sat short _Accum,_Sat _Accum,_Sat long _Accum,_Sat long long _Accum,_Sat unsigned short _Accum,_Sat unsigned _Accum,_Sat unsigned long _Accum,_Sat unsigned long long _Accum.

Fixed-point data values contain fractional and optional integral parts.The format of fixed-point data varies and depends on the target machine.

Support for fixed-point types includes:

• prefix and postfix increment and decrement operators (++,--)
• unary arithmetic operators (+,-,!)
• binary arithmetic operators (+,-,*,/)
• binary shift operators (<<,>>)
• relational operators (<,<=,>=,>)
• equality operators (==,!=)
• assignment operators (+=,-=,*=,/=,<<=,>>=)
• conversions to and from integer, floating-point, or fixed-point types

Use a suffix in a fixed-point literal constant:

• ‘hr’ or ‘HR’ forshort _Fract and_Sat short _Fract
• ‘r’ or ‘R’ for_Fract and_Sat _Fract
• ‘lr’ or ‘LR’ forlong _Fract and_Sat long _Fract
• ‘llr’ or ‘LLR’ forlong long _Fract and_Sat long long _Fract
• ‘uhr’ or ‘UHR’ forunsigned short _Fract and_Sat unsigned short _Fract
• ‘ur’ or ‘UR’ forunsigned _Fract and_Sat unsigned _Fract
• ‘ulr’ or ‘ULR’ forunsigned long _Fract and_Sat unsigned long _Fract
• ‘ullr’ or ‘ULLR’ forunsigned long long _Fractand_Sat unsigned long long _Fract
• ‘hk’ or ‘HK’ forshort _Accum and_Sat short _Accum
• ‘k’ or ‘K’ for_Accum and_Sat _Accum
• ‘lk’ or ‘LK’ forlong _Accum and_Sat long _Accum
• ‘llk’ or ‘LLK’ forlong long _Accum and_Sat long long _Accum
• ‘uhk’ or ‘UHK’ forunsigned short _Accum and_Sat unsigned short _Accum
• ‘uk’ or ‘UK’ forunsigned _Accum and_Sat unsigned _Accum
• ‘ulk’ or ‘ULK’ forunsigned long _Accum and_Sat unsigned long _Accum
• ‘ullk’ or ‘ULLK’ forunsigned long long _Accumand_Sat unsigned long long _Accum

GCC support of fixed-point types as specified by the draft technical reportis incomplete:

• Pragmas to control overflow and rounding behaviors are not implemented.

Fixed-point types are supported by the DWARF debug information format.

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